Biomechanical Basis of Human Movement, 3rd Edition

Section II - Functional Anatomy

Chapter 6

Functional Anatomy of the Lower Extremity


After reading this chapter, the student will be able to:

  1. Describe the structure, support and movements of the hip, knee, ankle, and subtalar joints.
  2. Identify the muscular actions contributing to movements at the hip, knee and ankle joints.
  3. List and describe some of the common injuries to the hip, knee, ankle, and foot.
  4. Discuss strength differences between muscle groups acting at the hip, knee, and ankle.
  5. Develop a set of strength and flexibility exercises for the hip, knee, and ankle joints.
  6. Describe how alterations in the alignment in the lower extremity influences function at the knee, hip, ankle, and foot.
  7. Discuss the structure and function of the arches of the foot.
  8. Identify the lower extremity muscular contributions to walking, running, stair climbing, and cycling.
  9. Discuss various loads on the hip, knee, ankle, and foot in daily activities.


The lower extremities are subject to forces that are generated via repetitive contacts between the foot and the ground. At the same time, the lower extremities are responsible for supporting the mass of the trunk and the upper extremities. The lower limbs are connected to each other and to the trunk by the pelvic girdle. This establishes a link between the extremities and the trunk that must always be considered when examining movements and the muscular contributions to movements in the lower extremity.

Movement in any part of the lower extremity, pelvis, or trunk influences actions elsewhere in the lower limbs. Thus, a foot position or movement can influence the position or movement at the knee or hip of either limb, and a pelvic position can influence actions throughout the lower extremity (23). It is important to evaluate movement and actions in both limbs, the pelvis, and the trunk rather than focus on a single joint to understand lower extremity function for the purpose of rehabilitation, sport performance, or exercise prescription.

For example, in a simple kicking action, it is not just the kicking limb that is critical to the success of the skill. The contralateral limb plays a very important role in stabilization and support of body weight. The pelvis establishes the correct positioning for the lower extremity, and trunk positioning determines the efficiency of the lower extremity musculature. Likewise, in evaluating a limp in walking, attention should not be focused exclusively on the limb in which the limp occurs because something happening in the other extremity may cause the limp.

The Pelvis and Hip Complex

Pelvic Girdle

The pelvic girdle, including the hip joint, plays an integral role in supporting the weight of the body while offering mobility by increasing the range of motion in the lower extremity. The pelvic girdle is a site of muscular attachment for 28 trunk and thigh muscles, none of which are positioned to act solely on the pelvic girdle (130). Similar to the shoulder girdle, the pelvis must be oriented to place the hip joint in a favorable position for lower extremity movement. Therefore, concomitant movement of the pelvic girdle and the thigh at the hip joint is necessary for efficient joint actions.

The pelvic girdle and hip joints are part of a closed kinetic chain system whereby forces travel up from the lower extremity through the hip and the pelvis into the trunk or down from the trunk through the pelvis and the hip to the lower extremity. Finally, pelvic girdle and hip joint positioning contribute significantly to the maintenance of balance and standing posture by using continuous musculat action to fine-tune and ensure equilibrium.

The pelvic region is one area of the body where there are noticeable differences between the sexes in the general population. As illustrated in Figure 6-1, women generally have pelvic girdles that are lighter, thinner, and wider than their counterparts in men (66). The female pelvis flares out more laterally in the front. The female sacrum is also wider in the back, creating a broader pelvic cavity than in men. This skeletal difference is discussed later in this chapter because it has a direct influence on muscular function in and around the hip joint.


FIGURE 6-1 The pelvis of a female is lighter, thinner, and wider than that of a male. The female pelvis also flares out in the front and has a wider sacrum in the back.




FIGURE 6-2 The pelvic girdle supports the weight of the body, serves as an attachment site for numerous muscles, contributes to the efficient movements of the lower extremity, and helps maintain balance and equilibrium. The girdle consists of two coxal bones, each created through the fibrous union of the ilium, ischium, and pubic bones. The right and left coxal bones are joined anteriorly at the pubic symphysis (A), and connect posteriorly (B) via the sacrum and the two sacroiliac joints.

The bony attachment of the lower extremity to the trunk occurs via the pelvic girdle (Fig. 6-2). The pelvic girdle consists of a fibrous union of three bones: the superior ilium, the posteroinferior ischium, and the anteroinferior pubis. These are separate bones connected by hyaline cartilage at birth but are fully fused, or ossified, by age 20 to 25 years.

The right and left sides of the pelvis connect anteriorly at the pubic symphysis, a cartilaginous joint that has a fibrocartilage disc connecting the two pubic bones. The ends of each pubic bone are also covered with hyaline cartilage. This joint is firmly supported by a pubic ligament that runs along the anterior, posterior, and superior sides of the joint. Movement at this joint is limited, maintaining a firm connection between right and left sides of the pelvic girdle.

The pelvis is connected to the trunk at the sacroiliac joint, a strong synovial joint containing fibrocartilage and powerful ligamentous support (Fig. 6-2). The articulating surface on the sacrum faces posteriorly and laterally and articulates with the ilium, which faces anteriorly and medially (165).

The sacroiliac joint transmits the weight of the body to the hip and is subject to loads from the lumbar region and from the ground. It is also an energy absorber of shear forces during gait (130). Three sets of ligaments support


the left and right sacroiliac joints, and these ligaments are the strongest in the body (Fig. 6-3).


FIGURE 6-3 Ligaments of the pelvis and hip region shown for the anterior (A) and posterior (B) perspective and for the hip joint (C).



Even though the sacroiliac joint is well reinforced by very strong ligaments, movement occurs at the joint. The amount of movement allowed at the joint varies considerably between individuals and sexes. Males have thicker and stronger sacroiliac ligaments and consequently do not have mobile sacroiliac joints. In fact, three in 10 men have fused sacroiliac joints (165).

In females, the sacroiliac joint is more mobile because there is greater laxity in the ligaments supporting the joint. This laxity may increase during the menstrual cycle, and the joint is extremely lax and mobile during pregnancy (60).

Another reason the sacroiliac joint is more stable in males is related to positioning differences in the center of gravity. In the standing position, body weight forces the sacrum down, tightening the posterior ligaments and forcing the sacrum and ilium together. This provides stability to the joint and is the close-packed position for the sacroiliac joint (130). In females, the center of gravity is in the same plane as the sacrum, but in males, the center of gravity is more anterior. Thus, in males, a greater load is placed on the sacroiliac joint, which in turn creates a tighter and more stable joint (165).

Motion at the sacroiliac joint can best be described by sacral movements. The movements of the sacrum that accompany each specific trunk movement are presented in Figure 6-4. The triangular sacrum is actually five fused vertebrae that move with the pelvis and trunk. The top of the sacrum, the widest part, is the base of the sacrum, and when this base moves anteriorly, it is termed sacral flexion (130). Clinically, this is also referred to as nutation. This movement occurs with flexion of the trunk and with bilateral flexion of the thigh.

Sacrum extension, or counternutation, occurs as the base moves posteriorly with trunk extension or bilateral thigh extension. The sacrum also rotates along an axis running diagonally across the bone. Right rotation is designated if the anterior surface of the sacrum faces to the right and left rotation if the anterior surface faces to the left. This sacral torsion is produced by the piriformis muscle in a side-bending exercise of the trunk (130). Additionally, in the case of asymmetrical movement such as standing on one leg, there can be asymmetrical movement at the sacroiliac joint, which results in torsion of the pelvis.


FIGURE 6-4 A. In the neutral position, the sacrum is placed in the close-packed position by the force of gravity. The sacrum responds to movements of both the thigh and the trunk. B. When the trunk extends or the thigh flexes, the sacrum flexes. Flexion of the sacrum occurs when the wide base of the sacrum moves anteriorly. C. During trunk flexion or thigh extension, the sacrum extends as the base moves posteriorly. The sacrum also rotates to the right or left with lateral flexion of the trunk (not shown).




FIGURE 6-5 The pelvis moves in six directions in response to a trunk or thigh movement. Anterior tilt of the pelvis accompanies trunk flexion or thigh extension (A). Posterior tilt accompanies trunk extension or thigh flexion (B). Left (C) and right (D) lateral tilt accompany weight bearing on the right and left limbs, respectively, or lateral movements of the thigh or trunk. Left (E) and right (F) rotation accompany left and right rotation of the trunk, respectively, or unilateral leg movement.

In addition to the movement between the sacrum and the ilium, there is movement of the pelvic girdle as a whole. These movements, shown in Figure 6-5, accompany trunk and thigh movements to facilitate positioning of the hip joint and the lumbar vertebrae. Although muscles facilitate the movements of the pelvis, no one set of muscles acts on the pelvis specifically; thus, pelvic movements occur as a consequence of movements of the thigh or the lumbar vertebrae.

Movements of the pelvis are described by monitoring the ilium, specifically, the anterior-superior, and anteriorinferior iliac spines on the front of the ilium. In a closedchain weight-bearing movement, the pelvis moves about a fixed femur, and anterior tilt of the pelvis occurs when the trunk flexes and the hip flexes. In an open-chain position such as hanging, the femur moves on the pelvis, and anterior tilt occurs with extension of the thighs. This anterior tilt can be created by protruding the abdomen and creating a swayback position in the low back. Both anterior tilt and posterior tilt in an open-chain movement can substitute for hip extension and hip flexion, respectively (Fig. 6-6). In a closed-chain movement, posterior tilt is created through trunk extension or flattening of the low back and hip extension. In the open chain, posterior tilt occurs with flexion of the thigh.


FIGURE 6-6 The pelvis can assist with movements of the thigh by tilting anteriorly to add to hip extension (left) or tilt posteriorly to add to hip flexion (right).

The pelvis can also tilt laterally and naturally tries to move through a right lateral tilt when weight is supported by the left limb. In the closed-chain weight-bearing position, if the right pelvis elevates, adduction of the hip is produced on the weight-bearing limb and abduction of the hip is produced on the opposite side to which the pelvis drops. This movement is controlled by muscles, particularly the gluteus medius, so that it is not pronounced unless the controlling muscles are weak. Thus, right and left lateral tilt occur with weight bearing and any lateral movement of the thigh or trunk (Fig. 6-7).

Finally, the pelvic girdle rotates to the left and right as unilateral leg movements take place. As the right limb swings forward in a walk, run, or kick, the pelvis rotates to the left. Hip external rotation accompanies the forward pelvis, and hip internal rotation accompanies the backward pelvic side.

Hip Joint

The final joint in the pelvic girdle complex is the hip joint, which can be generally characterized as stable yet mobile. The hip, which has 3 degrees of freedom (df), is a balland-socket joint consisting of the articulation between the acetabulum on the pelvis and the head of the femur. The structure of the hip joint and femur is illustrated in Figure 6-8.




FIGURE 6-7 In the lower extremity, segments interact differently depending on whether an open- or closed-chain movement is occurring. As shown on the left, the hip abduction movement in the open chain occurs as the thigh moves up toward the pelvis. In the closed-chain movement shown on the right, bduction occurs as the pelvis lowers on the weightbearing side.

The acetabulum is the concave surface of the ball and socket, facing anteriorly, laterally, and inferiorly (119,133). Interestingly, the three bones forming the pelvis–the ilium, ischium, and pubis–make their fibrous connections with each other in the acetabular cavity. The cavity is lined with articular cartilage that is thicker at the edge and thickest on the top part of the cavity (77,119). There is no cartilage on the underside of the acetabulum. As with the shoulder, a rim of fibrocartilage called the acetabular labrum encircles the acetabulum. This structure serves to deepen the socket and increase stability (152).

The spherical head of the femur fits snugly into the acetabular cavity, giving the joint both congruency and a large surface contact area. Both the femoral head and the acetabulum have large amounts of spongy trabecular bone that facilitates the distribution of the forces absorbed by the hip joint (119). The head is also lined with articular cartilage that is thicker in the middle central portions of the head, where most of the load is supported. The cartilage on the head thins out at the edges, where the acetabular cartilage is thick (119). Approximately 70% of the head of the femur articulates with the acetabulum compared with 20% to 25% for the head of the humerus with the glenoid cavity.

Surrounding the whole hip joint is a loose but strong capsule that is reinforced by ligaments and the tendon of the psoas muscle and encapsulates the entire femoral head and a good portion of the femoral neck. The capsule is densest in the front and top of the joint, where the stresses are the greatest, and it is quite thin on the back side and bottom of the joint (143).

Three ligaments blend with the capsule and receive nourishment from the joint (Fig. 6-3). The iliofemoral




ligament, or Y-ligament, is strong and supports the anterior nip joint in the standing posture Acromiong extension, external rotation, and some adduction (152). This ligament is capable of supporting most of the body weight and plays an important role in standing posture (123). Also, hyperextension may be so limited by this ligament that it may not actually occur in the hip joint itself but rather as a consequence of anterior pelvic tilt.


FIGURE 6-8 The hip is a stable joint with considerable mobility in three directions. It is formed by the concave surface of the acetabulum on the pelvis and the large head of the femur. The femur is one of the strongest bones in the body.

The second ligament on the front of the hip joint, the pubofemoral ligament, primarily resists abduction, with some resistance to external rotation and extension. The final ligament on the outside of the joint is the ischiofemoral ligament, on the posterior capsule, where it resists extension, adduction, and internal rotation (152). None of the ligaments surrounding the hip joint resist during flexion movements, and all are loose during flexion. This makes flexion the movement with the greatest range of motion.

The femur is held away from the hip joint and the pelvis by the femoral neck. The neck is formed by cancellous trabecular bone with a thin cortical layer for strength. The cortical layer is reinforced on the lower surface of the neck, where greater strength is required in response to greater tension forces. Also, the medial femoral neck is the portion responsible for withstanding ground reaction forces. The lateral portion of the neck resists compression forces created by the muscles (119).

The femoral neck joins up with the shaft of the femur, which slants medially down to the knee. The shaft is very narrow in the middle, where it is reinforced with the thickest layer of cortical bone. Also, the shaft bows anteriorly to offer the optimal structure for sustaining and supporting high forces (143).

The femoral neck is positioned at a specific angle in both the frontal and transverse planes to facilitate congruent articulation within the hip joint and to hold the femur away from the body. The angle of inclination is the angle of the femoral neck with respect to the shaft of the femur in the frontal plane. This angle is approximately 125° (143) (Fig. 6-9). This angle is larger at birth by almost 20° to 25°, and it gets smaller as the person matures and assumes weight-bearing positions. It is also believed that the angle continues to reduce by approximately 5° in later adult years.


FIGURE 6-9 The angle of inclination of the neck of the femur is approximately 125°. If the angle is less than 125°, it is termed coxa vara. When the neck angle is greater than 125°, it is termed coax valga.

The range of the angle of inclination is usually within 90° to 135° (119). The angle of inclination is important because it determines the effectiveness of the hip abductors, the length of the limb, and the forces imposed on the hip joint (Fig. 6-10). An angle of inclination greater than 125° is termed coxavalga. This increase in the angle of inclination lengthens the limb, reduces the effectiveness of the hip abductors, increases the load on the femoral head, and decreases the stress on the femoral neck (152). Coxa vara, in which the angle of inclination is less than 125°, shortens the limb, increases the effectiveness of the hip abductors, decreases the load on the femoral head, and increases stress on the femoral neck. This varus position gives the hip abductors a mechanical advantage needed to counteract the forces produced by body weight. The result is reductions in the load imposed on the hip joint and in the amount of muscular force needed to counteract the force of body weight (143). There is a higher prevalence of coax vara in athletic females than males (122).

The angle of the femoral neck in the transverse plane is termed the angle of anteversion (Fig. 6-11). Normally the femoral neck is rotated anteriorly 12° to 14° with respect to the femur (152). Anteversion in the hip increases the mechanical advantage of the gluteus maximus, making it more effective as an external rotator (133). Conversely, there is reduced efficiency of the gluteus medius and vastus medialis, resulting in a loss of control of motion in the frontal and transverse plan (122). If there is excessive anteversion in the hip joint, in which it rotates beyond 14° to the anterior side, the head of the femur is uncovered, and a person must assume an internally rotated posture or gait to keep the femoral head in the joint socket. The toeingin accompanying excessive femoral anteversion is illustrated in Figure 6-12. Other accompanying lower extremity adjustments to excessive anteversion include an increase in the Q-angle, patellar problems, long legs,


more pronation at the subtalar joint, and an increase in lumbar curvature (119,143). Excessive anteversion has also been associated with increased hip joint contact forces and higher bending moments (63) as well as higher patellofemoral joint contact pressures (122).


FIGURE 6-10 The femoral neck inclination angle influences both load on the femoral neck and the effectiveness of the hip abductors. When the angle is reduced in coxa vara, the limb is shortened and the abductors are more effective because of a longer moment arm resulting in less load on the femoral head but more load on the femoral neck. The coax valgus position lengthens the limb, reduces the effectiveness of the abductors because of a shorter moment arm, increases the load on the femoral head, and decreases the load on the neck.

If the angle of anteversion is reversed so that it moves posteriorly, it is termed retroversion (Fig. 6-11). Retroversion creates an externally rotated gait, a supinated foot, and a decrease in the Q-angle (143).

The hip is one of the most stable joints in the body because of powerful muscles, the shape of the bones, the labrum, and the strong capsule and ligaments (123). The hip is a stable joint even though the acetabulum is not deep enough to cover all of the femoral head. The acetabular labrum deepens the socket to increase stability, and the joint is in a close-packed position in full extension when the lower body is stabilized on the pelvis. The joint is stabilized by gravity during stance, when body weight presses the femoral head against the acetabulum (143). There is also a difference in atmospheric pressure in the hip joint, creating a vacuum and suction of the femur up into the joint. Even if all of the ligaments and muscles were removed from around the hip joint, the femur would still remain in the socket (75).


FIGURE 6-11 The angle of the femoral neck in the frontal plane is called the angle of anteversion. The normal angle is approximately 12° to 14° to the anterior side. If this angle increases, a toe-in position is created in the extremity. If the angle of anteversion is reversed so the femoral neck moves posteriorly, it is termed retroversion. Retroversion causes toeing out.




FIGURE 6-12 Individuals who have excessive femoral anteversion compensate by rotating the hip medially so that the knees face medially in stance. There is also usually an adaptation in the tibia that develops external tibial torsion to reorient the foot straight ahead.

Strong ligaments and muscular support in all directions support and maintain stability in the hip joint. At 90° of flexion with a small amount of rotation and abduction, there is maximum congruence between the femoral head and the socket. This is a stable and comfortable position and is common in sitting. A position of instability for the hip joint is in flexion and adduction, as when the legs are crossed (75).

Movement Characteristics

The hip joint allows the thigh to move through a wide range of motion in three directions (Fig. 6-13). The thigh can move through 120° to 125° of flexion and 10° to 15° of hyperextension in the sagittal plane (57,119). These measurements are made with respect to a fixed axis and vary considerably if measured with respect to the pelvis (7). Also, if thigh extension is limited or impaired, compensatory joint actions at the knee or in the lumbar vertebrae accommodate the lack of hip extension.

Hip flexion range of motion is limited primarily by the soft tissue and can be increased at the end of the range of motion if the pelvis tilts posteriorly. Hip flexion occurs freely with the knees flexed but is severely limited by the hamstrings if the flexion occurs with knee extension (75).

Extension is limited by the anterior capsule, the strong hip flexors, and the iliofemoral ligament. Anterior tilt of the pelvis contributes to the range of motion in hip extension.

The thigh can abduct through approximately 30° to 45° and can adduct 15° to 30° beyond the anatomical position (75). Most activities require 20° of abduction and adduction (75). Abduction is limited by the adductor muscles, and adduction is limited by the tensor fascia latae muscle.


FIGURE 6-13 The thigh can move through a wide range of motion in three directions. The thigh moves through approximately 120° to 125° of flexion, 10 to 15° of hyperextension, 30° to 45° of abduction, 15° to 30° of adduction, 30° to 50° of external rotation, and 30 to 50° of internal rotation.

Finally, the thigh can internally rotate through 30° to 50° and externally rotate through 30° to 50° from the anatomical position (75,131). The range of motion for rotation at the hip can be enhanced by the position of the thigh. Both internal and external rotation ranges of motion can be increased by flexing the thigh (75). Both internal and external rotation are limited by their antagonistic muscle group and the ligaments of the hip joint. Range of motion in the hip joint is usually lower in older age groups, but the difference is not that substantial and is usually in the range of 3° to 5° (137).

Combined Movements of the Pelvis and Thigh

The pelvis and the thigh commonly move together unless the trunk restrains pelvic activity. The coordinated movement between the pelvis and the hip joint is termed the




pelvifemoral rhythm. In hip flexion movements in an open chain (leg raise), the pelvis rotates posteriorly in the first degrees of motion. In a leg raise with the knees flexed or extended, 26% to 39% of the hip flexion motion is attributed to pelvic rotation, respectively (36). At the end of the range of motion in hip flexion, additional posterior pelvic rotation can contribute to more hip flexion. Anterior pelvic tilt accompanies hip extension when the limb is off the ground. In running, the average anterior tilt of the swing limb has been shown to be approximately 22°, which increases if there is limited hip extension flexibility (145). There is more pelvic motion in non-weight-bearing motions.

Range of motion at the hip, knee, and ankle in common activities


Hip Range of Motion

Knee Range of Motion

Ankle/Foot Range of Motion


·   35°–40° of flexion during late swing (119)

·   Full extension at heel lift

·   12° of abduction and tion after toe-off; max adduction in stance) (75,143)

·   8°–10° of external rotation in swing phase of gait (75)

·   4°–6° of internal rotation before heel strike and through the support Phase

·   5°–8° of knee flexion at heel strike (157)

·   60°–88° of knee flexion during swing phase (78,157)

·   17°–20° of flexion during support (78,157)

·   12°–17° of rotation during swing phase (78,157)

·   8°–11° of valgus during swing phase (78,157)

·   5°–8° of knee flexion at heel strike (157)

·   17°–20° of flexion during support (78,83,157)

·   5°–7° of internal rotation during support (78,83,157)

·   7°–14° of external rotation during support (78,83,157)

·   3°–7° of varus during support (78,83,157)

·   20°–40° of total ankle movement

·   10° of plantarflexion at heel strike (128)

·   5°–10° of dorsiflexion in midstance (128)

·   20° of plantarflexion at toe-off (128)

·   Dorsiflexion back to the neutral position in the swing phase (168)

·   4° of calcaneal inversion at toe-off (89)

·   6°–7° of calcaneal eversion in midstance (89)

·   2°–3° of supination at heel strike (39)

·   3°–10° of pronation at midstance (8,31,157)

·   3°–10° of supination up until heel-off (62)



·   80° of knee flexion during swing phase (55)

·   36°of flexion during support (55)

·   8° of valgus during swing phase(55)

·   19° of varus during support (55)

·   8° of internal rotation during support (55)

·   11° of external rotation during support (55)

·   10° of dorsiflexion prior To contact (157)

·   As much as 50° of dorsiflexion in midstance (157)

·   25° of plantarflexion at toe-off (157)

·   8°–15° of pronation in midstance (8,31,157)

Lowering into or raising out of a chair

·   80°–100° of flexion (65)

·   93° of flexion, 15° of abduction/ adduction and 14° of rotation (85)


Climbing stairs

·   63° of flexion for ascent; 24°–30° for descent (65,143)

·   83° of flexion, 17° of abduction, and 16° of rotation for ascent (85)

·   83° of flexion, 14°of abduction/ adduction and 15° of rotation for descent (85)

Bending down and picking up an object

·   18°–20° of abduction (143)

·   10°–15° of external rotation (143)


Tying a shoe while seated


·   106°of flexion, 20°of abduction/ adduction, 18° of rotation

In a closed-chain, weight-bearing, standing position, the pelvis moves anteriorly on the femur, and pelvic motion during hip flexion has been shown to contribute only 18% to the change in hip motion (110). Posterior pelvic motion in weight bearing contributes to hip extension.

In the frontal plane, pelvic orientation is maintained or adjusted in response to single-limb weight bearing seen in walking or running. When weight is taken onto one limb, there is a mediolateral shift toward the nonsupport limb that requires abduction and adduction muscle torque to shift the pelvis toward the stance foot (73). This elevation of the nonsupport side pelvis creates hip adduction on the support side and abduction on the nonsupport side.

In the transverse plane during weight bearing, a rotation forward of the pelvis on one side creates lateral rotation on the front hip and medial rotation on the back hip.

Muscular Actions

The insertion, action, and nerve supply for each individual muscle in the lower extremity are outlined in Figure 6-14. Thigh flexion is used in walking and running to bring the leg forward. It is also an important movement in climbing stairs and walking uphill and is forcefully used in kicking. Little emphasis is placed on training the hip joint for flexion movements because most consider flexion at the hip to play a minor role in activities. However, hip flexion is very important for sprinters, hurdlers, high jumpers, and others who must develop quick leg action. Elite athletes in these activities usually have proportionally stronger hip flexors and abdominal muscles than do less skilled athletes. Recently, more attention has been given to training of the hip flexors in long distance runners as well because it has been shown that fatigue in the hip flexors during running may alter gait mechanics and lead to injuries that may be avoidable with better conditioning of this muscle group.

The strongest hip flexor is the iliopsoas muscle, which consists of the psoas major, psoas minor, and iliacus (143). The iliopsoas is a two-joint muscle that acts on both the lumbar spine of the trunk and the thigh. If the trunk is stabilized, the iliopsoas produces flexion at the hip joint that is slightly facilitated with the thigh abducted and externally rotated. If the thigh is fixed, the iliopsoas produces hyperextension of the lumbar vertebrae and flexion of the trunk.

The iliopsoas is highly activated in hip flexion exercises where the whole upper body is lifted or the legs are lifted (6). In sit-ups with the hips flexed and the feet held in place, the hip flexors are more active. Also, double leg lifts result in much higher activity in the iliopsoas than single leg lifts (6).

The rectus femoris is another hip flexor whose contribution depends on knee joint positioning. This is also a two-joint muscle because it acts as an extensor of the knee joint as well. It is called the kicking muscle because it is in maximal position for output at the hip during the preparatory phase of the kick, when the thigh is drawn back into hyperextension and the leg is flexed at the knee. This position puts the rectus femoris on stretch and into an optimal length-tension relationship for the succeeding joint action, in which the rectus femoris makes a powerful contribution to both hip flexion and knee extension. During the kicking action, the rectus femoris is very susceptible to injury and avulsion at its insertion site, the anterior inferior spine on the ilium. Loss of function of the rectus femoris diminishes thigh flexion strength as much as 17% (96).

The three other secondary flexors of the thigh are the sartorius, pectineus, and tensor fascia latae (see Fig. 6-14). The sartorius is a two-joint muscle originating at the anterior superior iliac spine and crossing the knee joint to the medial side of the proximal tibia. It is a weak fusiform muscle producing abduction and external rotation in addition to the flexion action of the hip.

The pectineus is one of the upper groin muscles. It is primarily an adductor of the thigh except in walking, actively contributing to thigh flexion. It is accompanied by the tensor fascia latae, which is generally an internal rotator. During walking, however, the tensor fascia latae aids thigh flexion. The tensor fascia latae is considered a two-joint muscle because it attaches to the fibrous band of fascia, the iliotibial band, running down the lateral thigh and attaching across the knee joint on the lateral aspect of the proximal tibia. Thus, this muscle is stretched in knee extension.

During thigh flexion, the pelvis is pulled anteriorly by these muscles unless stabilized and counteracted by the trunk. The iliopsoas muscle and tensor fascia latae pull the pelvis anteriorly. If either of these muscles is tight, pelvic torsion, pelvic instability, or a functional short leg may occur.

Extension of the thigh is important in the support of the body weight in stance because it maintains and controls the hip joint actions in response to gravitational pull. Thigh extension also assists in propelling the body up and forward in walking, running, or jumping by producing hip joint actions that counteract gravity. The extensors attach to the pelvis and consequently play a major role in stabilizing the pelvis in the anterior and posterior directions.

The muscles contributing in all conditions of extension at the hip joint are the hamstrings. The two medial




hamstrings–the semimembranosus and the semitendinosus–are not as active as the lateral hamstring, the biceps femoris, which is considered the workhorse of extension at the hip.


FIGURE 6-14 Muscles acting on the hip joint, including the adductors and flexors (A), the external rotators (B), abductors (C), and extensors (D). A combination of knee and hip joint muscles comprise the anterior thigh region (E, F).

Because all of the hamstrings cross the knee joint, producing both flexion and rotation of the lower tibia, their effectiveness as hip extensors depends on positioning at the knee joint. With the knee joint extended, the hamstrings are put on stretch for optimal action at the hip. The hamstring output also increases with increasing amounts of thigh flexion; however, the hamstrings can be lengthened to a position of muscle strain if the leg is extended with the thigh in maximal flexion.

The hamstrings also control the pelvis by pulling down on the ischial tuberosity, creating a posterior tilt of the pelvis. In this manner, the hamstrings are responsible for maintaining an upright posture. Tightness in the hamstrings can create significant postural problems by flattening the low back and producing a continuous posterior tilt of the pelvis.

In level walking or in low-output hip extension activities, the hamstrings are the predominant muscles that contributed to the extension movement in the weight-bearing positions. Loss of function in the hamstrings produces significant impairment in hip extension.

If the resistance in extension is increased or if a more vigorous hip extension is needed, the gluteus maximus is recruited as a major contributor (152). This occurs in running up hills, climbing stairs, rising out of a deep squat, sprinting, and rising from a chair. It also occurs in an optimal length-tension position with thigh hyperex-tension and external rotation (152).

The gluteus maximus appears to dominate the pelvis during gait rather than contribute significantly to the generation of extension forces. Because the thigh is almost extended during the walking cycle, the function of the gluteus maximus is more trunk extension and posterior tilt of the pelvis. At foot strike when the trunk flexes, the gluteus maximus prevents the trunk from pitching forward. Because the gluteus maximus also externally rotates the thigh, internal rotation places the muscle on stretch. Loss of function of the gluteus maximus muscle does not significantly impair the extension strength of the thigh because the hamstrings dominate production of extension strength (96).

Finally because the flexors and extensors control the pelvis anteroposteriorly, it is important that they are balanced in both strength and flexibility so that the pelvis is not drawn forward or backward as a result of one group being stronger or less flexible.

Abduction of the thigh is an important movement in many dance and gymnastics skills. During gait, the abduction and the abduction muscles are more important in their role as stabilizers of the pelvis and thigh. The abductors can raise the thigh laterally in the frontal plane, or if the foot is on the ground, they can move the


pelvis on the femur in the frontal plane. When abduction occurs, such as in doing splits on the ground, both hip joints displace the same number of degrees in abduction, even though only one limb may have moved. The relative angle between the thigh and the trunk is the same in both hip joints in abduction because of the pelvic shift in response to abduction initiated in one hip joint.

The main abductor of the thigh at the hip joint is the gluteus medius. This multipennate muscle contracts during the stance in a walk, run, or jump to stabilize the pelvis so that it does not drop to the nonstance limb. This is important for all the joints and segments in the lower extremity because a weak gluteus medius can lead to changes such as contralateral pelvis drop and increased femoral adduction and internal rotation, which can lead to increased knee valgus, excessive lateral tracking of the patella, and increased tibial rotation and pronation in the foot (44). The effectiveness of the gluteus medius muscle is determined by its mechanical advantage. It is more effective if the angle of inclination of the femoral neck is less than 125°, taking the insertion further away from the hip joint, and it is also more effective for the same reason in the wider pelvis (133). As the mechanical advantage of the gluteus medius increases, the stability of the pelvis in gait will also improve.

The gluteus minimus, tensor fascia latae, and piriformis also contribute to abduction of the thigh, with the gluteus minimus being the most active of the three. A 50% reduction in the function of the abductors results in a slight to moderate impairment in abduction function (96). If the abductors are weak, there will be an excessive tilt in the frontal plane, with a higher pelvis on the weaker side (88). The abductors on the support side work to keep the pelvis level and to avoid any tilting. Additionally, the shear forces across the sacroiliac joint will greatly increase, and the individual will walk with greater side-to-side sway.

The adductor muscle group works to bring the thigh across the body, as seen commonly in dance, soccer, gymnastics, and swimming. The adductors, similar to the abductors, also work to maintain the pelvic position during gait. The adductors as a group constitute a large muscle mass, with all of the muscles originating on the pubic bone and running down the inner thigh. Although the adductors are important in specific activities, it has been shown that a 70% reduction in the function of the thigh adductors results in only a slight or moderate impairment in hip function (96).

The adductor muscles include the gracilis, on the medial side of the thigh; the adductor longus, on the anterior side of the thigh; the adductor brevis, in the middle of the thigh; and the adductor magnus, on the posterior side of the inner thigh. High in the groin is the pectineus, previously discussed briefly in its role as hip flexor. The adductors are active during the swing phase of gait as they work to swing the limb through (152), and if they are tight, a scissors gait can result, leading to a crossover plant.

The adductors work with the abductors to balance the pelvis. The abductors on one side of the pelvis work with the adductors on the opposite side to maintain pelvic positioning and prevent tilting. As shown earlier, the abductors and adductors must be balanced in strength and flexibility so that the pelvis can be balanced side to side. Figure 6-15 illustrates how imbalances in abduction and adduction can tilt the pelvis. If the abductors overpower the adductors through contracture or a strength imbalance, the pelvis will tilt to the side of the strong, contracted abductor. Adductor contracture or strength imbalances produce a similar effect in the opposite direction. The adductors also work with the hip flexors and extensors to maintain limb position and to counteract the rotation of the pelvis when the front limb is flexed and the back limb is extended in the double-support phase of walking (123).

External rotation of the thigh is important in preparation for power production in the lower extremity because it follows the trunk during rotation. The muscles primarily responsible for external rotation are the gluteus max-imus, obturator externus, and quadratus femoris. The obturator internus, inferior and superior gemellus, and piriformis contribute to external rotation when the thigh is extended. The piriformis also abducts the hip when the hip is flexed and creates the movement on lifting the leg into abduction with the toes pointing upward in external rotation. Because most of these muscles attach to the anterior face of the pelvis, they also exert considerable control over the pelvis and sacrum.

Internal rotation of the thigh is basically a weak movement. It is a secondary movement for all of the muscles contracting to produce this joint action. The two muscles most involved in internal rotation are the gluteus medius and the gluteus minimus. Internal rotation is also aided by contractions of the gracilis, adductor longus, adductor magnus, tensor fascia latae, semimembranosus, and semi-tendinosus.

The muscles of the trunk, pelvis, and hip also work together to control the pelvic posture. The pelvis serves as a link between the lumbar vertebrae and the hip and must be stabilized by the trunk or thigh musculature to maintain its position (135). For example, at the beginning of lifting, the gluteus maximus contracts to stabilize pelvis so that the spinal extensors can extend the trunk in the lift. The gluteus maximus also stabilizes the pelvis in trunk rotation (112). In upright standing, the pelvis is maintained in a vertical position but can also assume a variety of tilt postures. The rectus femoris and the erector spinae muscles can pull the pelvis anteriorly, and the gluteals and abdominals can pull the pelvis posteriorly if the pelvis is in a position out the neutral vertical position (43,135).

Strength of the Hip Joint Muscles

The hip muscles generate the greatest strength output in extension. The most massive muscle in the body, the gluteus maximus, combines with the


hamstrings to produce hip extension. Extension strength is maximum with the hip flexed to 90° and diminishes by about half as the hip flexion angle approaches the 0° or neutral position (152). Extension strength also depends on knee position because the hamstrings cross the knee joint. The hamstrings' contribution to hip extension strength is enhanced with the knees extended (75).


FIGURE 6-15 The abductors and adductors work in pairs to maintain pelvic height and levelness. For example, the left abductors work with the right adductors and lateral trunk flexors to create a left lateral tilt. If an abductor or adductor muscle group is stronger than the contralateral group, the pelvis will tilt to the strong side. This also happens with contracture of the muscle group.

Many muscles contribute to hip flexion strength, but many of the muscles do so secondarily to other main roles. Hip flexion strength is primarily generated with the powerful iliopsoas muscle, although its strength diminishes with trunk flexion. Additionally, the flexion strength of the thigh can be enhanced if flexion at the knee joint increases the contribution of the rectus femoris to flexion strength. Abduction strength is maximal from the neutral position and diminishes more than half at 25° of abduction (152). This reduction is associated with decreases in muscle length even though the ability of the gluteus medius to abduct the leg improves as a consequence of improving the direction of the pull of the muscle. The strength output of the abduction movement can also be increased if it is performed with the thigh flexed (152). Abduction strength has also been shown to be greater in the dominant limb than in the nondominant limb (71,115).

The potential for the development of adduction strength is substantial because the muscles contributing to the movement are massive as a group and adductors can develop more force output than the abductors (97). Adduction, however, is not the primary contributor to many movements or sport activities, so it is minimally loaded or strengthened through activity. Adduction strength values are greater from a position of slight abduction as a stretch is placed on the muscle group.

The strength of the external rotators is 60% greater than that of the internal rotators except in hip flexion, when the internal rotators are slightly stronger (152). The strength output of both the internal and external rotators is greater in a seated position than in a supine one.

Conditioning of the Hip Joint Muscles

The muscles surrounding the hip joint receive some form of conditioning during walking, rising from or lowering into a chair, and performing other common daily activities, such as climbing stairs. The hip musculature should be balanced so that the extensors do not overpower the flexors and the abductors are equivalent to the adductors. This ensures sufficient control over the pelvis. Sample stretching and strengthening exercises for the hip joint muscles are provided in Figure 6-16.

Because the hip muscles are used in all support activities, it is best to design exercises using a closed kinetic chain. In this type of activity, the foot or feet are in contact






with a surface (i.e., the ground), and forces are applied to the system at the foot or feet. An example of a closed-chain exercise is a squat lift in weight training. An example of an open kinetic chain exercise is one using a machine, in which the muscle group moves the limb through a prescribed arc of motion. Finally, many two-joint muscles act at the hip joint, so careful attention should be paid to adjacent joint positioning to maximize a stretch or strengthening exercise.


FIGURE 6-16 Sample stretching and strengthening exercises for selected muscle groups.

The flexors are best exercised in the supine or hanging position so that the thigh can be raised against gravity or in lifting the whole upper body. The hip flexors are minimally used in a lowering activity, such as a squat, when there is flexion of the thigh, because the extensors control the movement eccentrically. Because the hip flexors attach on the trunk and across the knee joint, their contribution to flexion can be enhanced with the trunk extended. Flexion at the knee also enhances thigh flexion. It is easy to stretch the flexors with both the trunk and thigh placed in hyperextension. The rectus femoris can be placed in a very strenuous stretch with thigh hyperextension and maximal knee flexion.

The success of conditioning the extensors depends on trunk and knee joint positioning. The greater the knee flexion, the less the hamstrings contribute to extension, requiring a greater contribution from the gluteus max-imus. For example, in a quarter-squat activity with the extensors used eccentrically to lower the body and concentrically to raise the body, the hamstrings are the most active contributors. In a deep squat, with the amount of knee flexion increased to 90° and beyond, the gluteus maximus is used more because the hamstrings are incapacitated by their reduced length.

Trunk positioning is also important, and the activity of the hamstrings is enhanced with trunk flexion because trunk flexion increases the length of both the hamstrings and the gluteus maximus. The extensors are best exercised in a standing, weight-supported position because they are used in this position in most cases and are one of the propulsive muscle groups in the lower extremity.

The extensors can be stretched to maximum levels with hip flexion accompanied by full extension at the knee. The stretch on the gluteus maximus can be increased with thigh internal rotation and adduction.

The abductors and adductors are difficult to condition because they influence balance and pelvic position so significantly In a standing position, the thigh can be abducted against gravity, but it will shift the pelvis dramatically so that the person loses balance. The adductors present an even greater problem. It is very difficult to place the adductors so that they work against gravity because the abductors are responsible for lowering the limb to the side after abducting it. Consequently, the supine position is best for strengthening and stretching the abductors and adductors. Resistance can be offered manually or through an exercise machine with external resistance to the movement.

The abductors and adductors can be exercised from the sidelying position so that they can work against gravity. This position requires stabilization of the pelvis and low back. It is hard to exercise the abductors or adductors on one side without working the other side as well; both sides are affected equally because of the action of the pelvis. For example, 20° of abduction at the right hip joint results in 20° of abduction at the left hip joint because of the pelvic tilt accompanying the movement.

The rotators of the thigh are the most challenging in terms of conditioning because it is so difficult to apply resistance to the rotation. The seated position is recommended for strengthening the rotators because the rotators are strong in this position and resistance to the rotation can easily be applied to the leg either with surgical tubing or manually. Because the internal rotators lose effectiveness in the extended supine position, they should definitely be exercised with the person seated. Both muscle groups can be stretched in the same way they are strengthened, using the opposite joint action for the stretch. These exercises may be contraindicated, however, for individuals with knee pain, particularly patellofemoral pain.

Injury Potential of the Pelvic and Hip Complex

Injuries to the pelvis and hip joint are a small percentage of injuries in the lower extremity. In fact, overuse injuries to this area account for only 5% of the total for the whole body (129). This may be attributable to the strong ligamentous support, significant muscular support, and solid structural characteristics of the region.

Injuries to the pelvis primarily occur in response to abnormal function that excessively loads areas of the pelvis. This can result in an irritation at the site of muscular attachment, and in adolescents, a more common type of injury might be an avulsion fracture at the apophysis, or bony outgrowth. Iliac apophysitis is an example of such an injury, in which excessive arm swing in gait causes excessive rotation of the pelvis, creating stress on the attachment site of the gluteus medius and tensor fascia latae on the iliac crest (129). This can also occur at the iliac crest as a result of direct blow or as a result of a sudden, violent contraction of the abdominals (3,104). A hip pointer results when the anterior iliac crest is bruised as a result of a direct blow. Apophysitis, an inflammation of an apophysis, can also develop into a stress fracture.

Another site in the pelvis subjected to apophysitis or stress fracture is the anterior superior iliac spine where the sartorius attaches (104) and high tensions develop in activities such as sprinting where there is vigorous hip extension and knee flexion. At the anterior inferior iliac spine, the rectus femoris can produce the same type of injury in an activity such as kicking.

A stress fracture in the pubic rami can be produced by strong contractions from the adductors, often associated with overstriding in a run (159). Finally, the hamstrings


can exert enough force to create an avulsion fracture on the ischial tuberosity. Commonly called the hurdler's fracture, this ischial tuberosity injury is also common to waterskiing (5). All of these injuries are most common in activities such as sprinting, jumping, soccer, football, basketball, and figure skating, in which sudden bursts of motion are required (104).

The sacrum and sacroiliac joint can dysfunction as a result of injury or poor posture. If one assumes a round-shouldered, forward-head posture, the center of gravity of the body moves forward. This increase in the curvature of the lumbar spine produces a ligamentous laxity in the dorsal sacroiliac ligaments and stress on the anterior ligaments (40). Also, any skeletal asymmetry, such as a short leg, produces a ligament laxity in the sacroiliac joint (130).

With excessive mobility, large forces are transferred to the sacroiliac joint, producing an inflammation of the joint known as sacroiliitis. Inflammation of the joint may occur in an activity such as long jumping, in which the landing is absorbed with the leg extended at the knee. At the same time, the hip is flexed or there is extreme flexion of the trunk combined with lateral flexion (130). The sacroiliac joint also becomes very mobile in pregnant women, making them more susceptible to sacroiliac sprain (60).

The functional positions of the sacrum and the pelvis are also important for maintaining an injury-free lower extremity. A functional short leg can be created by posterior rotation of the ipsilateral ilium, anterior ilium rotation of the opposite side, superior ilium movement on the same side, forward or backward sacral torsion to the same side, or sacral flexion of the opposite side (130). A functional short leg requires adjustments in the whole limb, creating stress at the sacroiliac joint, knee, and foot.

The hip joint can withstand large loads, but when muscle imbalance develops with high forces, injury can result. For example, in a high-force situation involving flexion, adduction, and internal rotation, a dislocation posteriorly can occur. Falling on an adducted limb with the knee flexed or an abrupt stop over the weight-bearing limb can push the femoral head to the posterior rim of the acetabulum, resulting in a hip subluxation (5). Activities more prone to a posterior dislocation of the hip are stooping activities, leg-crossing activities, or rising from a low seat (113). Anterior dislocations or subluxations are uncommon.

Also, a number of age-related hip conditions must be considered when working with children or older adults. In children 3 to 12 years old, the condition known as Legg-Calvé-Perthes disease may appear (143). In this condition, also called coxa plana, the femoral head degenerates, and the proximal femoral epiphysis is damaged. This disorder strikes boys five times more frequently than girls and usually occurs to only one limb (2). It is caused by trauma to the joint, synovitis or inflammation to the capsule, or some vascular condition that limits blood supply to the area.

Slipped capital femoral epiphysitis is another disorder that can affect children aged 10 to 17 years. It is usually caused by some traumatic event that forces the femoral neck into external rotation, or it can be caused by failure of the cartilaginous growth plates (2). This tilts the femoral head back and medially and tilts the growth plate forward and vertically, producing a nagging pain on the front of the thigh. An individual with this disorder walks with an externally rotated gait and has limited internal rotation with the thigh flexed and abducted (143). Such slippage may occur in a baseball player who rounds a base with the left foot fixed in internal rotation while the trunk and pelvis rotate in the opposite direction.

The final major childhood disorder to the hip joint is congenital hip dislocation, a disorder that affects girls more often than boys (143). This condition is usually diagnosed early as the infant assumes weight on the lower extremity. The hip joint subluxates or dislocates for no apparent reason. The thigh cannot abduct, the limb shortens, and a limp is usually present. Fortunately, this condition is easily corrected with an abduction orthotic.

An age-related disorder of the hip joint seen commonly in elderly individuals is osteoarthritis. This condition results in degeneration of the joint cartilage and the underlying subchondral bone, narrowing of the joint space, and the growth of osteophytes in and around the joint. This affliction strikes millions of elderly people, creating a significant amount of pain and discomfort during weight support and gait activities. To reduce the pain in the joint, individuals often assume a position of flexion, adduction, and external rotation or whichever position results in the least tension for the hip.

More than 60% of injuries to the hip occur in the soft tissue (88). Of these injuries, 62% occur in running, 62% are associated with a varum alignment in the lower extremity, and 30% are associated with a leg length discrepancy (88). These types of injuries are usually muscle strains, tendinitis of the muscle insertions, or bursitis (25).

The most common soft tissue injury to the hip region is gluteus medius tendinitis, which occurs more frequently in women as a result of excessive pull by the gluteus medius during running (21,88). A hamstring strain is also common and is seen in activities such as hurdling, in which the lower limb is placed in a position of maximum hip flexion and knee extension. It can also occur with speed or hill running and in individuals performing with poor flexibility or conditioning in this muscle group.

Iliopsoas strain can occur in activities such as sprinting, in which a rapid forceful flexion taxes the muscle or the muscle is used eccentrically to slow a rapid extension at the hip. The adductors are often strained in an activity such as soccer, in which the lower extremity is rapidly abducted and externally rotated in preparation for contact with the ball. Strain to the rectus femoris can occur in a rapid forceful flexion of the thigh, such as is seen in sprinting, and in a vigorous hyperextension of the thigh, such as in the preparatory phase of a kick.

A piriformis strain may be caused by excessive external rotation and abduction when the thigh is being flexed.


This creates pain in adduction, flexion, and internal rotation of the thigh. A piriformis syndrome can develop. This is an impingement of the sciatic nerve aggravated by internal and external rotation movement of the thigh during walking (21,88). The syndrome can also be created by a functional short leg that lengthens the piriformis and then stretches it as the pelvis drops to the shorter leg. The irritation of the sciatic nerve causes pain in the buttock area that can travel down the posterior surface of the thigh and leg.

Other soft tissue injuries to the hip region are seen in the bursae. The most common of these is greater trochanteric bursitis, which is caused by hyperadduction of the thigh. This can be produced by running with too much leg crossover in each stride, imbalance between the abductors and adductors, running on banked surfaces, having a leg length difference, or remaining on the outside of the foot during the support phase of a walk or run (22,129). It is especially prevalent in runners with a wide pelvis, a large Q-angle, and an imbalance between the abductors and adductors (22,129).

Because the right hip adductors work with the left hip abductors and vice versa, any imbalance causes asymmetrical posture. For example, a weak right abductor creates a lateral pelvic tilt, with the right side high and the left side low. This places stress on the lateral hip, setting up the conditions for bursitis. Pain on the outside of the hip is accentuated with trochanteric bursitis when the legs are crossed.

Ischial bursitis can develop with prolonged sitting and is aggravated by walking, stair climbing, and flexion of the thigh. Finally, iliopectineal bursitis may develop in reaction to a tight iliopsoas muscle or osteoarthritis of the hip (143).

Two remaining soft tissue injuries seen in dancers and distance runners are lateral hip pain created by iliotibial band syndrome and snapping hip syndrome. The strain to the iliotibial band is created because dancers warm up with the hip abducted and externally rotated. They have very few flexion and extension routines in warmup and dance routines. The stress to the iliotibial band occurs with thigh adduction and internal rotation, movements that are extremely limited in dancers by technique (136). Iliotibial band syndrome can also be caused by excess tension in the tensor fascia latae in abducting the hip in single-stance weight bearing. The snapping hip also commonly produces a click as the hip capsule moves or the iliopsoas tendon snaps over a bony surface.

The bony or osseous injuries to the hip are usually a result of a strong muscular contraction that creates an avulsion fracture. Stress fractures can develop in the hip region and are common in endurance athletes, particularly women (25). Stress fractures to the femoral neck account for 5% to 10% of all stress fractures (98). A stress fracture to the inferior medial aspect of the femoral neck is seen more often in younger patients and is caused by high compression forces. In older adults, stress fractures to the femoral neck are seen more often on the superior side and are caused by high tension forces (3). The abductors can create an avulsion fracture on the greater trochanter, and the iliopsoas can pull hard enough to produce an avulsion fracture at the lesser trochanter (3,143). Stress fractures can also appear in the femoral neck. It is believed that these stress fractures may be related to some type of vascular necrosis in which the blood supply is limited or to some hormonal deficiency that reduces the bone density in the neck (88). Stress fracture at this site produces pain in the groin area.

The Knee Joint

The knee joint supports the weight of the body and transmits forces from the ground while allowing a great deal of movement between the femur and the tibia. In the extended position, the knee joint is stable because of its vertical alignment, the congruency of the joint surfaces, and the effect of gravity. In any flexed position, the knee joint is mobile and requires special stabilization from the powerful capsule, ligaments, and muscles surrounding the joint (148). The joint is vulnerable to injury because of the mechanical demands on it and the reliance on soft tissue for support.

The ligaments surrounding the knee support the joint passively as they are loaded in tension only. The muscles support the joint actively and are also loaded in tension, and bone offers support and resistance to compressive loads (101). Functional stability of the joint is derived from the passive restraint of the ligaments, joint geometry, the active muscles, and the compressive forces pushing the bones together.

There are three articulations in the region known as the knee joint: the tibiofemoral joint, the patellofemoral joint, and the superior tibiofibular joint (166). The bony landmarks of the knee joint and tibia and fibula are illustrated in Figure 6-17.

Tibiofemoral Joint

The tibiofemoral joint, commonly referred to as the actual knee joint, is the articulation between the two longest and strongest bones in the body, the femur and the tibia (Fig. 6-17). It has been referred to as a double condyloid joint or a modified hinge joint that combines a hinge and a pivot joint. In this joint, flexion and extension occur similar to flexion and extension at the elbow joint. In the knee joint, however, flexion is accompanied by a small but significant amount of rotation (148).

At the distal end of the femur are two large convex surfaces, the medial and lateral condyles, separated by the intercondylar notch in the posterior and the patellar, or trochlear, groove in the anterior (148) (Fig. 6-17). It is important to review the anatomical characteristics of these two condyles because their differences and the




corresponding differences on the tibia account for the rotation in the knee joint. The lateral condyle is flatter, has a larger surface area, projects more posteriorly, is more prominent anteriorly to hold the patella in place, and is basically aligned with the femur (166). The medial condyle projects more distally and medially, is longer in the anteroposterior direction, angles away from the femur in the rear, and is aligned with the tibia (166). Above the condyles on both sides are the epicondyles, which are the sites of capsule, ligament, and muscular attachment.


FIGURE 6-17 The structure of the knee joint is complex with asymmetrical condyles on the distal end of the femur articulating with asymmetrical facets on the tibial plateau. The patella moves in the trochlea groove on the femur. The anterior (A) and posterior (B) views of the lower leg and a close-up view of the knee joint (C) illustrate the complexity of the joints.

The condyles rest on the condyle facet or tibial plateau, a medial and lateral surface separated by a ridge of bone termed the intercondylar eminence. This ridge of bone serves as an attachment site for ligaments, centers the joint, and stabilizes the bones in weight bearing (166). The medial surface of the plateau is oval, larger, longer in the anteroposterior direction, and slightly concave to accept the convex condyle of the femur. The lateral tibial plateau is circular and slightly convex (166). Consequently, the medial tibia and femur fit fairly snugly together, but the lateral tibia and femur do not fit together well because both surfaces are convex (148). This structural difference is one of the determinants of rotation because the lateral condyle has a greater excursion with flexion and extension at the knee.

Two separate fibrocartilage menisci lie between the tibia and the femur. As shown in Figure 6-18, the lateral meniscus is oval, with attachments at the anterior and posterior horns (53,166). It also receives attachments from the quadriceps femoris anteriorly and the popliteus muscle and posterior cruciate ligament (PCL) posteriorly. The lateral meniscus occupies a larger percentage of the area in the lateral compartment than the medial meniscus in the medial compartment. Also, the lateral meniscus is more mobile, capable of moving more than twice the distance of the medial meniscus in the anteroposterior direction (166).

The medial meniscus is larger and crescent shaped, with a wide base of attachment on both the anterior and posterior horns via the coronary ligaments (Fig. 6-18). It is connected to the quadriceps femoris and the anterior cruciate ligament (ACL) anteriorly, the tibial collateral ligament laterally, and the semimembranosus muscle posteriorly (166).

Both menisci are wedge shaped because of greater thickness at the periphery. The menisci are connected to each other at the anterior horns by a transverse ligament. The menisci have blood supply to the horns at the anterior and posterior ends of the arcs of each meniscus but have no blood supply to the inner portion of the fibrocartilage. Thus, if a tear occurs in the periphery of the menisci, healing can occur, unlike with tears to the thinner inner portion of the menisci.

The menisci are important in the knee joint. The menisci enhance stability in the joint by deepening the contact surface on the tibia. They participate in shock absorption by transmitting half of the weight-bearing load in full extension and a significant portion of the load in flexion (170). In flexion, the lateral meniscus carries the greater portion of the load. By absorbing some of the load, the menisci protect the underlying articular cartilage and subchondral bone. The menisci transmit the load across the surface of the joint, reducing the load per unit of area on the tibiofemoral contact sites (53). The contact area in the joint is reduced by two thirds when the menisci are absent. This increases the pressure on the contacting surfaces and increases the susceptibility to injury (116). During low-load situations, the contact is primarily on the menisci, but in high-load situations, the contact area increases, with 70% of the load still on the menisci (53). The lateral meniscus carries a significantly greater percentage of the load.


FIGURE 6-18 Two fibrocartilage menisci lie in the lateral and medial compartments of the knee. The medial meniscus is crescent shaped, and the lateral meniscus is oval to match the surfaces of the tibial plateau and the differences in the shape of the femoral condyles. Both menisci serve important roles in the knee joint by offering shock absorption, stability, and lubrication and by increasing the contact area between the tibia and the femur.

The menisci also enhance lubrication of the joint. By acting as a space-filling mechanism, they allow dispersal of more synovial fluid to the surface of the tibia and the femur. It has been demonstrated that a 20% increase in friction within the joint occurs with the removal of the meniscus (170).

Finally, the menisci limit motion between the tibia and femur. In flexion and extension, the menisci move with the femoral condyles. As the leg flexes, the menisci move


posteriorly because of the rolling of the femur and muscular action of the popliteus and semimembranosus muscles (170). At the end of the flexion movement, the menisci fill up the posterior portion of the joint, acting as a space-filling buffer. The reverse occurs in extension. The quadriceps femoris and the patella assist in moving the menisci forward on the surface. Additionally, the menisci follow the tibia during rotation.

The tibiofemoral joint is supported by four main ligaments, two collateral and two cruciate. These ligaments assist in maintaining the relative position of the tibia and femur so that contact is appropriate and at the right time. See Figure 6-19 for insertions, actions, and illustration of these ligaments. They are the passive load-carrying structures of the joint and serve as a backup to the muscles (101).

On the sides of the joint are the collateral ligaments. The medial collateral ligament (MCL) is a flat, triangular ligament that covers a large portion of the medial side of the joint. The MCL supports the knee against any valgus force (a medially directed force acting on the lateral side of the knee) and offers some resistance to both internal and external rotation (118). It is taut in extension and reduces in length by approximately 17% in full flexion (167). The MCL offers 78% of the total valgus restraint at 25° of knee flexion (120).

The lateral collateral ligament (LCL) is thinner and rounder than the MCL. It offers the main resistance to varus force (a lateral force acting on the medial side) at the knee. This ligament is also taut in extension and reduces its length by approximately 25% in full flexion (167). The LCL offers 69% of the varus restraint at 25° of knee flexion (120) and offers some support in lateral rotation.

In full extension, the collateral ligaments are assisted by tightening of the posteromedial and posterolateral capsules, thus making the extended position the most stable (100). Both collaterals are taut in full extension even though the anterior portion of the MCL is also stretched in flexion.

The cruciate ligaments are intrinsic, lying inside the joint in the intercondylar space. These ligaments control both anteroposterior and rotational motion in the joint. The anterior cruciate ligament (ACL) provides the primary restraint for anterior movement of the tibia relative to the femur. It accounts for 85% of the total restraint in this direction (120). The ACL is 40% longer than its counterpart, the PCL. It elongates by about 7% as the knee moves from extension to 90° of flexion and maintains the same length up through maximum flexion (167). If the joint is internally rotated, the insertion of the ACL moves anteriorly, elongating the ligament slightly more. With the joint externally rotated, the ACL does not elongate up through 90° of knee flexion but elongates up to 10% from 90° to full flexion (167). Different parts of the ACL are taut in different knee positions. The anterior fibers are taut in extension, the middle fibers are taut in internal rotation, and the posterior fibers are taut in flexion. The ACL as a whole is considered to be taut in the extended position (Fig. 6-20).

The PCL offers the primary restraint to posterior movement of the tibia on the femur, accounting for 95% of the total resistance to this movement (120). This ligament decreases in length and slackens by 10% at 30° of knee flexion and then maintains that length throughout flexion (167). The PCL increases in length by about 5% with internal rotation of the joint up to 60° of flexion and then decreases in length by 5% to 10% as flexion continues. The PCL is not affected by external rotation in the joint, maintaining a fairly constant length. It is maximally strained through 45° to 60° of flexion (167) (Fig. 6-20). As with the ACL, the fibers of the PCL participate in different functions. The posterior fibers are taut in extension, the anterior fibers are taut in midflexion, and the posterior fibers are taut in full flexion; however, as a whole, the PCL is taut in maximum knee flexion.

Both the cruciate ligaments stabilize, limit rotation, and cause sliding of the condyles over the tibia in flexion. They both also offer some stabilization against varus and valgus forces. In a standing posture, with the tibial shaft vertical, the femur is aligned with the tibia and tends to slide posteriorly. A hyperextended position to 9° of flexion is unstable because the femur tilts posteriorly and is minimally restricted (101). At a 9° tilt of the tibia, the femur slides anteriorly to a position where it is more stable and supported by the patella and the quadriceps femoris.

Another important support structure surrounding the knee is the joint capsule. One of the largest capsules in the body, it is reinforced by numerous ligaments and muscles, including the MCL, the cruciate ligaments, and the arcuate complex (166). In the front, the capsule forms a substantial pocket that offers a large patellar area and is filled with the infrapatellar fat pad and the infrapatellar bursa. The fat pad offers a stopgap in the anterior compartment of the knee.

The capsule is lined with the largest synovial membrane in the body, which forms embryonically from three separate pouches (18). In 20% to 60% of the population, a permanent fold, called a plica, remains in the synovial membrane (19). The common location of plica is medial and superior to the patella. It is soft and pliant and passes over the femoral condyle in flexion and extension. If injured, it can become fibrous and create both resistance and pain in motion (19). There are also more than 20 bur-sae in and around the knee, reducing friction between muscle, tendon, and bone (166).

Patellofemoral Joint

The second joint in the region of the knee is the patellofemoral joint, consisting of the articulation of the patella with the trochlear groove on the femur. The patella is a triangular sesamoid bone encased by the tendons of the quadriceps femoris. The primary role of the patella is to increase the mechanical advantage of the quadriceps femoris (18).




FIGURE 6-19 Ligaments of the knee joint shown from the anterior (A), posterior (B), and medial (C) perspective.




FIGURE 6-20 The anterior cruciate ligament provides anterior restraint of the movement of the tibia relative to the femur. The posterior cruciate ligament offers restraint to posterior movement of the tibia relative to the femur.

The posterior articulating surface of the patella is covered with the thickest cartilage found in any joint in the body (148). A vertical ridge of bone separates the underside of the patella into medial and lateral facets, each of which can be further divided into superior, middle, and inferior facets. A seventh facet, the odd facet, lies on the far medial side of the patella (166). The structure of the patella and the location of these facets are presented in Figure 6-21. During normal flexion and extension, five of these facets typically make contact with the femur.

The patella is connected to the tibial tuberosity via the strong patellar tendon. It is connected to the femur and tibia by small patellofemoral and patellotibial ligaments that are actually thickenings in the extensor retinaculum surrounding the joint (18).

Positioning of the patella and alignment of the lower extremity in the frontal plane is determined by measuring the Q-angle (quadriceps angle). Illustrated in Figure 6-22,


the Q-angle is formed by drawing one line from the anterior superior spine of the ilium to the middle of the patella and a second line from the middle of the patella to the tibial tuberosity. The Q-angle forms because the two condyles sit horizontal on the tibial plateau and because the medial condyle projects more distally, the femur angles laterally. In a normal alignment, the hip joint should still be vertically centered over the knee joint even though the anatomical alignment of the femur angles out. The most efficient Q-angle for quadriceps femoris function is one close to 10° of valgus (92). Whereas males typically have Q-angles averaging 10° to 14°, females average 15° to 17°, speculated to be primarily because of their wider pelvic basins (92). However, a recent evaluation of the Q-angle in males and females suggests that the positioning of the anterior superior iliac spine is not significantly positioned more laterally in females, and the differences in values between males and females are attributable to height differences (59).


FIGURE 6-21 The patella increases the mechanical advantage of the quadriceps femoris muscle group. The patella has five facets, or articulating surfaces: the superior, inferior, medial, lateral, and odd facets.


FIGURE 6-22 The Q-angle is measured between a line from the anterior superior iliac spine to the middle of the patella and the projection of a line from the middle of the patella to the tibial tuberosity. Q-angles range from 10° to 14° for males and 15° to 17° for females. Very small Q-angles create a condition known as genu varum, or bowleggedness. Large Q-angles create genu valgrum, or knock-kneed position.

The Q-angle represents the valgus stress acting on the knee, and if it is excessive, many patellofemoral problems can develop. Any Q-angle over 17° is considered to be excessive and is termed genu valgum, or knock-knees (92). A very small Q-angle constitutes bowleggedness, or genu varum.

Mediolaterally, the patella should be centered in the trochlear notch, and if the patella deviates medially or laterally, abnormal stresses can develop on the underside. The vertical position of the patella is determined primarily by the length of the patellar tendon measured from the distal end of the patella to the tibia. Patella alta is an alignment in which the patella is high and has been associated with higher levels of patellar subluxations. Patella baja is when the patella is lower than normal.


FIGURE 6-23 The tibiofibular joint is a small joint between the head of the fibula and the tibial condyle. It moves anteroposteriorly, superiorly, and inferiorly and rotates in response to movements of the tibia or the foot.

Tibiofibular Joint

The third and final articulation is the small, superior tibiofibular joint, shown in Figure 6-23. This joint consists of the articulation between the head of the fibula and the posterolateral and inferior aspect of the tibial condyle. It is a gliding joint moving anteroposteriorly, superiorly, and inferiorly and rotating in response to rotation of the tibia and the foot (132). The fibula externally rotates and moves externally and superiorly with dorsiflexion of the foot and accepts approximately 16% of the static load applied to the leg (132).

The primary functions of the superior tibiofibular joint are to dissipate the torsional stresses applied by the movements of the foot and to attenuate lateral tibial bending. Both the tibiofibular joint and the fibula absorb and control tensile rather than compressive loads applied to the lower extremity. The middle part of the fibula has more ability to withstand tensile forces than any other part of the skeleton (132).

Movement Characteristics

The function of the knee is complex because of its asymmetrical medial and lateral articulations and the patellar mechanics on the front. When flexion is initiated in the closed-chain or weight-bearing position, the femur rolls backward on the tibia and laterally rotates and abducts with respect to the tibia. In an open-chain movement such as kicking, flexion is initiated with movement of the tibia on the femur, resulting in tibial forward motion, medial rotation, and adduction. The opposite occurs in extension with the femur rolling forward, medially rotating, and adducting in a closed-chain movement and the tibia rolling backward, laterally rotating, and abducting in an open-chain activity. The femoral contact with the tibia moves posteriorly during flexion and anteriorly during extension. Through 120° of extension, the anterior movement is 40% of the length of the tibial plateau (166). It has also been suggested that after the rolling is complete in the flexion movement that the femur finishes off in maximal flexion by just sliding anteriorly. These movements are illustrated in Figure 6-24.

Rotation at the knee is created partly by the greater movement of the lateral condyle on the tibia through almost twice the distance. Rotation can occur only with the joint in some amount of flexion. Thus, there is no rotation in the extended, locked position. Internal tibial rotation also occurs with dorsiflexion and pronation at the foot. Roughly 6° of subtalar motion results in roughly 10° of internal rotation (141). External rotation of the tibia also accompanies plantarflexion and supination of the foot. With 34° of supination, there is a corresponding 58° of external rotation (141).

The rotation occurring in the last 20° of extension has been termed the screw-home mechanism. The screw-home mechanism is the point at which the medial and


lateral condyles are locked to form the close-packed position for the knee joint. The screw-home mechanism moves the tibial tuberosity laterally and produces a medial shift at the knee. Some of the speculative causes of the screw-home movement are that the lateral condyle surface is covered first and a rotation occurs to accommodate the larger surface of the medial condyle or that the ACL becomes taut just before rotation, forcing rotation of the femur on the tibia (149). Finally, it is speculated that the cruciate ligaments become taut in early extension and pull the condyles in opposite directions, causing the rotation. The screw-home mechanism is disrupted with injury to the ACL because the tibia moves more anteriorly on the femur. It is not significantly disrupted with loss of the PCL, indicating that the ACL is the main controller (149).


FIGURE 6-24 A. The movements at the knee joint are flexion and extension and internal and external rotation. B. When the knee flexes, there is an accompanying internal rotation of the tibia on the femur (non-weight bearing). In extension, the tibia externally rotates on the femur. C. There are also translatory movements of the femur on the tibial plateau surface. In flexion, the femur rolls and slides posteriorly.

The normal range of motion at the knee joint is approximately 130° to 145° in flexion and 1° to 2° of hyper extension. It has been reported that there is 6° to 30° of internal rotation through 90° of flexion at the joint around an axis passing through the medial intercondylar tubercle of the tibial plateau (78,119). External rotation of the tibia is possible through approximately 45° (75). The range of motion in varus or abduction and valgus or adduction is small and in the range of 5°.

When the knee flexes, the patella moves distally through a distance more than twice its length, entering the intercondylar notch on the femur (75) (Fig. 6-25). In extension, the patella returns to its resting position high and lateral on the femur, where it is above the trochlear groove and resting on the suprapatellar fat pad. The patella is free to move in the extended position and can be shifted in multiple directions. Patellar movement is restricted in the flexed position because of the increased contact with the femur.

The movement of the patella is most affected by the joint surface and the length of the patellar tendon and minimally affected by the quadriceps femoris. In the first 20° of flexion, the tibia internally rotates and the patella is drawn from its lateral position down into the groove, where first contact is made with the inferior facets (166). The stability offered by the lateral condyle is most important because most subluxations and dislocations of the patella occur in this early range of motion.

The patella follows the groove to 90° of flexion, at which point contact is made with the superior facets of the patella (Fig. 6-25). At that time, the patella again moves laterally over the condyle. If flexion continues to 135°, contact is made with the odd facet (166). In flexion, the linear and translatory movements of the patella


are posterior and inferior, but the patella also has some angular movements that affect its position. During knee flexion, the patella also flexes, abducts, and externally rotates, and these movements reverse in extension (extension, adduction, and internal rotation). Flexion and extension of the patella occur about a mediolateral axis running through a fixed axis in the distal femur, with flexion representing the upward tilt and extension representing the downward tilt about this axis. Likewise, patellar abduction and adduction involve movement of the patella away from and toward from midline in the frontal plane, respectively. External and internal rotation is rotation of the patella outward and inward about a longitudinal axis, respectively (82).


FIGURE 6-25 When the knee flexes, the patella moves inferiorly and posteriorly over two times its length. The patella sits in the groove and is held in place by the lateral condyle of the femur. If the knee continues into flexion past 90°, the patella moves laterally over the condyle until at approximately 135° of flexion, when contact is made with the odd facet.

Muscular Actions

Knee Extension Is A Very Important Contributor To The Generation of Power In The Lower Extremity For Any Form of Human Projection Or Translation. The Musculature Producing Extension Is Also Used Frequently To Contract Eccentrically and Decelerate A Rapidly Flexing Knee Joint. Fortunately, The Quadriceps Femoris Muscle Group, The Producer of Extension At The Knee, Is One of the Strongest Muscle Groups In The Body; It May Be As Much As Three Times Stronger Than Its Antagonistic Muscle Group, The Hamstrings, Because of Its Involvement In Negatively Accelerating The Leg and Continuously Contracting Against Gravity (75).

The quadriceps femoris is a muscle group that consists of the rectus femoris and vastus intermedius forming the middle part of the muscle group, the vastus lateralis on the lateral side, and the vastus medialis on the medial side (19). The specific insertions, actions, and nerve supply are presented in Figure 6-26.

The quadriceps femoris connect to the tibial tuberosity via the patellar tendon and contribute somewhat to the stability of the patella. As a muscle group, they also pull the menisci anteriorly in extension via the meniscopatellar ligament. When they contract, they also reduce the strain in the MCL and work with the PCL to prevent posterior displacement of the tibia. They are antagonistic to the ACL.

The largest and strongest of the quadriceps femoris is the vastus lateralis, a muscle applying lateral force to the patella. Pulling medially is the vastus medialis. The vastus medialis has two portions referred to as the vastus medialis longus and the vastus medialis oblique, and the boundary of these two portions of the vastus medialis is located at the medial rim of the patella . The direction of the muscle fibers in the more proximal vastus medialis longus runs more vertical, and the fibers of the lower vastus medialis oblique run more horizontal (124). Although the vastus medialis as a whole is an extensor of the knee, the vastus medialis oblique is also a medial stabilizer of the patella (166).

It has been noted in the literature that the vastus medialis was selectively activated in the last few degrees of extension. This has been proved not to be true. No selective activation of the vastus medialis muscles occurs in the last degrees of extension, and the quadriceps muscles contract equally throughout the range of motion (86).

The only two-joint muscle of the quadriceps femoris group, the rectus femoris, does not significantly contribute to knee extension force unless the hip joint is in a favorable position. It is limited as an extensor of the knee if the hip is flexed and is facilitated as a knee extensor if the hip joint is extended, lengthening the rectus femoris. In walking and running, the rectus femoris contributes to the extension force in the toe-off phase when the thigh is extended. Likewise, in kicking, rectus femoris activity is maximized in the preparatory phase as the thigh is brought back into hyperextension with the leg in flexion.

Flexion of the leg at the knee joint occurs during support, when the body lowers toward the ground; however, this downward movement is controlled by the extensors so that buckling does not occur. The flexor muscles are very active with the limb off the ground, working frequently to slow a rapidly extending leg.

The major muscle group that contributes to knee flexion is the hamstrings, consisting of the lateral biceps femoris and the medial semimembranosus and semitendinosus (see Fig. 6-26). The action of the hamstrings can be quite complex because they are two-joint muscles that work to extend the hip. The hamstrings work with the ACL to resist anterior tibial displacement. They are also rotators of the knee joint because of their insertions on the sides of the knee. As flexors, the hamstrings can generate the greatest force from a flexion position of 90° (121).

Flexion strength diminishes with extension because of an acute tendon angle that reduces the mechanical advantage. At full extension, flexion strength is reduced by 50% compared with 90° of flexion (121).

The lateral hamstring, the biceps femoris, has two heads connecting on the lateral side of the knee and offering lateral support to the joint. The biceps femoris also produces external rotation of the lower leg.

The semimembranosus bolsters the posterior and medial capsule. In flexion, it pulls the meniscus posteriorly (166). This medial hamstring also contributes to the production of internal rotation in the joint. The other medial hamstring, the semitendinosus, is part of the pes anserinus muscular attachment on the medial surface of the tibia. It is the most effective flexor of the pes anserinus muscle group, contributing 47% to the flexion force (166). The semitendinosus works with both the ACL and the MCL in supporting the knee joint. It also contributes to the generation of internal rotation.

The hamstrings operate most effectively as knee flexors from a position of hip flexion by increasing the length and tension in the muscle group. If the hamstrings become tight, they offer greater resistance to extension of the knee joint by the quadriceps femoris. This imposes a greater workload on the quadriceps femoris muscle group.

The two remaining pes anserinus muscles, the sartorius and the gracilis, also contribute 19% and 34% to the


flexion strength, respectively (121). The popliteus is a weak flexor that supports the PCL in deep flexion and draws the meniscus posteriorly. Finally, the two-joint gastrocnemius contributes to knee flexion, especially when the foot is in the neutral or dorsiflexed position.


FIGURE 6-26 Muscles acting on the knee joint. Shown are the anterior thigh muscles (A) with corresponding surface anatomy (B), the posterior thigh muscles (C) and posterior (D) and lateral (E) surface anatomy, and other supporting anterior and posterior muscles (F) (next page).

Internal rotation of the tibia is produced by the medial muscles: sartorius, gracilis, semitendinosus, semimembranosus, and popliteus (see Fig. 6-26). Internal rotation force is greatest at 90° of knee flexion and decreases by 59% at full extension (125,126). The internal rotation




force can be increased by 50% if it is preceded by 15° of external rotation. Of the three pes anserinus muscles, the sartorius and the gracilis are the most effective rotators, accounting for 34% and 40% of the pes anserinus force in rotation (121). The semitendinosus contributes 26% of the pes anserinus rotation force. The pes anserinus muscle group also contributes significantly to medial knee stabilization. Only one muscle, the biceps femoris, contributes significantly to the generation of external rotation of the tibia. Both internal and external rotation are necessary movements associated with function of the knee joint.

Combined Movements of the Hip and Knee

Many lower extremity movements require coordinated actions at the hip and knee joint, and this is complicated by the number of two-joint muscles that span both joints. Coactivation of both monarticular and biarticular agonists and antagonists is required to produce motion with appropriate direction and force. This coordination is required for uninterrupted transitions between extension and flexion. For example, in walking, coactivation of the gluteus maximus (monoarticular) and the rectus femoris (knee extensor) is necessary to generate forces for the simultaneous extension of both the hip and the knee (144,163,172). Additionally, coactivation of the iliopsoas and the hamstrings facilitate knee flexion by cancelling out the motion at the hip joint.

Positioning of the hip changes the effectiveness of the muscles acting at the knee joint. For example, changing the hip joint angle has a large effect on increasing the moment arm of the biceps femoris. It is the opposite for the rectus femoris, which is more influenced by a change in the knee angle (164). The range of motion at the knee also changes with a change in hip positioning. For example, the knee flexes through approximately 145° with the thigh flexed and 120° with the thigh hyperextended (75). This difference in range is attributable to the length-tension relationship in the hamstring muscle group.

Strength of the Knee Joint Muscles

The extensors at the knee joint are usually stronger than the flexors throughout the range of motion. Peak extension strength is achieved at 50° to 70° of knee flexion (116). The position of maximum strength varies with the speed of movement. For example, if the movement is slow, peak extension strength occurs in the first 20° of knee extension from the 90° flexed position. Flexion strength is greatest in the first 20° to 30° of flexion from the extended position (127). This position also fluctuates with the speed of movement. Greater knee flexion torques can be obtained if the hips are flexed because the hamstring length-tension relationship is improved.

It is common in sports medicine to evaluate the isokinetic strength of the quadriceps femoris and the hamstrings to construct a hamstring-to-quadriceps ratio. A generally acceptable ratio is 0.5, with the hamstrings at least half as strong as the quadriceps femoris. It has been suggested that anything below this ratio indicates a strength imbalance between the quadriceps femoris and the hamstrings that predisposes one to injury. Caution must be observed when using this ratio because it applies only to slow, isokinetic testing speeds.

At faster testing speeds, when the limbs move through 200° to 300°/sec, the ratio approaches 1 because the efficiency of the quadriceps femoris decreases at higher speeds. Even at the isometric testing level, the hamstring-to-quadriceps ratio is 0.7. Thus, a ratio of 0.5 between the hamstrings and the quadriceps femoris is not acceptable at fast speeds and indicates a strength imbalance between the two groups, but at a slower speed, it would not indicate an imbalance (111).

Internal and external rotation torques are both greatest with the knee flexed to 90° because a greater range of rotation motion can be achieved in that position. Internal rotation strength increases by 50% from 45° of knee flexion to 90° (126). The position of the hip joint also influences internal rotation torque, with the greatest strength developed at 120° of hip flexion, at which point the gracilis and the hamstrings are most efficient (125). At low hip flexion angles and in the neutral position, the sartorius is the most effective lateral rotator. Peak rotation torques occur in the first 5° to 10° of rotation. The internal rotation torque is greater than the external rotation torque (126).

Conditioning of the Knee Joint Muscles

The extensors of the leg are easy to exercise because they are commonly used both to lower and to raise the body. Examples of stretching and strengthening exercises for the extensors are presented in Figure 6-27. The squat is used to strengthen the quadriceps femoris. When one lowers into a squat, the force coming through the joint, directed vertically in the standing position, is partially directed across the joint, creating a shear force. This shear force increases as knee flexion increases. Thus, in a deep squat position, most of the original compressive force is directed posteriorly, creating a shear force. With the ligaments and muscles unable to offer much protection in the posterior direction at the full squat position, this is considered a vulnerable position. This position of maximum knee flexion is contraindicated for beginner and unconditioned lifters.

An experienced and conditioned lifter who has strong musculature and uses good technique at the bottom of the lift will most likely avoid any injury when in this position. Good technique involves control over the speed of descent and proper segmental positioning. For example, if the trunk is in too much flexion, the low back will be excessively loaded and the hamstrings will perform more of the work and the quadriceps femoris less, focusing control on the posterior side.




FIGURE 6-27 Sample stretching and strengthening exercises for selected muscle groups.



The quadriceps femoris group may also be exercised in an open-chain activity, as in a leg extension machine. Starting from 90° of flexion, one can exert considerable force because the quadriceps femoris muscles are very efficient throughout the early parts of the extension action. Near full extension, the quadriceps femoris muscles become inefficient and must exert greater force to move the same load. Thus, quadriceps activity in an open-chain leg extension is higher near full extension in the squat, but there is more activity in the quadriceps near full flexion at the bottom of the squat (49).

The terminal extension exercise is good for individuals who have patellar pain because the quadriceps femoris work hard with minimal patellofemoral compression force. This kind of exercise should be avoided, however, in early rehabilitation of an ACL injury because the anterior shear force is so large in this position. To minimize the stress on the ACL=, no knee extension exercise should be used at any angle less than 64° (169). Coactivation from the hamstrings increases as the knee reaches full extension, and this also minimizes the stress on the ACL by preventing anterior displacement (41). However, any knee extension exercise for individuals with ACL injuries should be done from a position of considerable knee flexion. Also, the terminal extension exercise does not selectively exercise the medial quadriceps more than the lateral quadriceps (45).

The flexors of the knee are not actively recruited in the performance of a flexion action with gravity because the quadriceps femoris muscles control the flexion action via eccentric muscle activity. Fortunately, the hamstrings are extensors of the hip as well as flexors of the knee joint. Thus, they are active during a squat exercise by virtue of their influence at the hip because hip flexion in lowering is controlled eccentrically by the hip extensors. The squat generates twice as much activity in the hamstrings as a leg press on a machine (49). If it were not for the hamstrings' role as extensors at the hip, the hamstrings group would be considerably weaker than the quadriceps femoris.

The knee flexors are best isolated and exercised in a seated position using a leg curl apparatus. The seated position places the hip in flexion, thus optimizing their performance. The knee flexors, especially the hamstrings and the pes anserinus muscles, are important for knee stability because they control much of the rotation at the knee. As presented earlier in this chapter, the hamstrings should be half as strong as the quadriceps femoris groups for slow speeds and should be as strong as the quadriceps femoris group at fast speeds. It is also important to maintain flexibility in the hamstrings because if they are tight, the quadriceps femoris muscles must work harder and the pelvis will develop an irregular posture and function.

The rotators of the knee, because they are all flexor muscles, are exercised along with the flexion movements. If the rotators are to be selectively stretched or strengthened as they perform the rotation, it is best to do the exercise from a seated position with the knee flexed to 90° and the rotators in a position of maximum effectiveness. Toeing in the foot contracts the internal rotators and stretches the external rotators. Different levels of resistance can be added to this exercise through the use of elastic bands or cables.

There continues to be debate over the use of closed-chain versus open-chain exercises for the rehabilitation after ACL repair at the knee joint. Some surgeons and physical therapists advocate using only closed-chain exercises (28). The reason behind this is that closed-chain exercises have been shown to produce significantly less posterior shear force at all angles and less anterior shear force at most angles (91). This occurs because of higher compressive loads and muscular coactivation. Recently, there has been added support for the inclusion of open-chain exercises in an ACL rehabilitation protocol (15). Knee extension exercises at angles of 60° to 90° have been shown to be very effective for isolation of quadriceps and do not negatively influence healing of the ACL graft (51). Studies have shown that anterior tibial translation is less in a closed-chain exercise (81), giving support for their use. In other studies, however, maximum ACL strains have been shown to be similar in both open- and closed-chain exercises (16), supporting the inclusion of both types of exercise in the rehabilitation protocol.

Extension exercises for individuals with patellofemoral pain also vary between closed- and open-chain exercises. In the open-chain knee extension, the patellofemoral force increases with extension with the quadriceps force high from 90° to 25° of knee flexion (45). In a closed-chain squat, it is opposite, with the patellofemoral force zero at full extension and increasing with increases in knee flexion and with load (14).

Injury Potential of the Knee Joint

The knee joint is a frequently injured area of the body, depending on the sport, accounting for 25% to 70% of reported injuries. In a 10-year study of athletic knee injuries in which 7769 injuries related to the knee joint were documented, the majority of the knee injuries occurred in males and in the age group of 20 to 29 years (94). Activities associated with most of the injuries were soccer and skiing.

The cause of an injury to the knee can often be related to poor conditioning or training or to an alignment problem in the lower extremity. Injuries in the knee have been attributable to hindfoot and forefoot varus or valgus, tibial or femoral varus or valgus, limb length differences, deficits in flexibility, strength imbalances between agonists and antagonists, and improper technique or training.

A number of knee injuries are associated with running or jogging because the knee and the lower extremity are subjected to a force equivalent to approximately three times body weight at every foot contact. It is clear that if 1500 foot contacts are made per mile of running, the potential for injury is high.



Traumatic injuries to the knee usually involve the ligaments. Ligaments are injured as a result of application of a force causing a twisting action of the knee. High-friction or uneven surfaces are usually associated with increased ligamentous injury. Any movement fixing the foot while the body continues to move forward, such as often occurs in skiing, will likely produce a ligament sprain or tear. Simply, any turn on a weight-bearing limb leaves the knee vulnerable to ligamentous injury.

The ACL is the most common site of ligament injuries, which are usually caused by a twisting action while the knee is flexed, internally rotated, and in a valgus position while supporting weight. It can also be damaged with a forced hyperextension of the knee. If the trunk and thigh rotate over a lower extremity while supporting the body's weight, the ACL can be sprained or torn because the lateral femoral condyle moves posteriorly in external rotation (61). The quadriceps can also be responsible for ACL sprain by producing anterior displacement of the tibia when eccentrically controlling knee motion when there is limited hamstring coactivation (32). If the hamstrings are co-contracting, they resist the anterior translation of the tibia. Examples from sport in which this ligament is often injured are skiers catching the edge of the ski; a football player being blocked from the side; a basketball player landing off balance from a jump, cutting, or rapid deceleration; and a gymnast landing off balance from a dismount (125).

Loss of the ACL creates valgus laxity and single-plane or rotatory instability (30). Whereas planar instability is usually anterior, rotatory instabilities can occur in a variety of directions, depending on the other structures injured (22). Instability created by an inefficient or missing ACL places added stress on the secondary stabilizers of the knee, such as the capsule, collateral ligaments, and iliotibial band. There is an accompanying deficit in quadriceps femoris musculature. The “side effects” of an ACL injury are often more debilitating in the long run.

Injury to the PCL is less common than to the ACL. The PCL is injured by receiving an anterior blow to a flexed or hyperextended knee or by forcing the knee into external rotation when it is flexed and supporting weight. Hitting the tibia up against the dashboard in a car crash or falling on a bent knee in soccer or football can also damage the PCL. Damage to the PCL results in anterior or posterior planar instability.

The collateral ligaments on the side are injured upon receipt of a force applied to the side of the joint. The MCL, torn in an application of force in the direction of the medial side of the joint, can also sprain or tear with a violent external rotation or tibial varus (35,151). The MCL is typically injured when the foot is fixed and slightly flexed. A change in direction with the person moving away from the support limb, as when running the bases in baseball, is a common event leading to an MCL injury. The MCL is usually injured at the proximal end, resulting in tenderness on the femoral side of the knee joint.

The LCL is injured upon receipt of a lateral force that is usually applied when the foot is fixed and the knee is in slight flexion (35). Injury to the MCL or LCL creates medial or lateral planar instabilities, respectively. A forceful varus or valgus force can also create a distal femoral epiphysitis as the collateral ligaments forcefully pull on their attachment site (84).

Damage to the menisci occurs much the same way as ligament damage. The menisci can be torn through compression associated with a twisting action in a weight-bearing position. They can also be torn in kicking and other violent extension actions. Tearing the meniscus by compression is a result of the femur grinding into the tibia and ripping the menisci. A meniscal tear in rapid extension is a result of the meniscus getting caught and torn as the femur moves rapidly forward on the tibia.

Tears to the medial meniscus are usually incurred during moves incorporating valgus, knee flexion, and external rotation in the supported limb or when the knee is hyper-flexed (148). Lateral meniscus tears have been associated with a forced axial movement in the flexed position; a forced lateral movement with impact on the knee in extension; a forceful rotational movement; a movement incorporating varus, flexion, and internal rotation of the support limb; and the hyperflexed position (148).

Many injuries to the knee are a result of less traumatic noncontact forces. Muscle strains to the quadriceps femoris or the hamstrings muscle groups occur frequently. Strain to the quadriceps femoris usually involves the rectus femoris because it can be placed in a very lengthened position with hip hyperextension and knee flexion. It is commonly injured in a kicking action, especially if the kick is mistimed. A hamstring strain is usually associated with inflexibility in the hamstrings or a stronger quadriceps femoris that pulls the hamstrings into a lengthened position. Sprinting when the runner is not in condition to handle the stresses of sprinting can lead to a hamstring strain.

On the lateral side of the knee is the iliotibial band, which is frequently irritated as the band moves over the lateral epicondyle of the femur in flexion and extension. Iliotibial band syndrome is seen in individuals who run on cambered roads, specifically affecting the downhill limb. It has also been identified in individuals who run more than 5 miles per session, in stair climbing and downhill running, and in individuals who have a varum alignment in the lower extremity (58). Medial knee pain can be associated with many structures, such as tendinitis of the pes anserinus muscle attachment and irritation of the semimembranosus, parapatellar, or pes bursae (58).

Posterior knee pain is likely associated with popliteus tendinitis, which causes posterior lateral pain. This is often brought on by hill running. Posterior pain can also be associated with strain or tendinitis of the gastrocnemius muscle insertion or by collection of fluid in the bursae, called a Baker's or popliteal cyst.

Anterior knee pain accounts for most overuse injuries to the knee, especially in women. Patellofemoral pain


 is pain around the patella and is often seen in individuals who exhibit valgum alignments or femoral anteversion in the extremity (34). Patellofemoral pain is aggravated by going down hills or stairs or squatting.

Stress on the patella is associated with a greater Q-angle because of increased stress on the patella. Patellar injury may be caused by abnormal tracking, which in addition to an increased Q-angle, can be created by a functional short leg, tight hamstrings, tight gastrocnemius, a long patellar tendon (termed patella alta), a short patellar tendon (termedpatella baja), a tight lateral retinaculum or iliotibial band, or excessive pronation at the foot.

Some patellofemoral pain syndromes are associated with cartilage destruction, in which the cartilage underneath the patella becomes soft and fibrillated. This condition is known aschondromalacia patellae. Patellar pain similar to that of patellar pain syndrome or chondromalacia patellae is also seen with medial retinaculitis, in which the medial retinaculum is irritated in running (166).

A subluxated or dislocated patella is common in individuals with predisposing factors. These are patella alta, ligamentous laxity, a small Q-angle with outfacing patella, external tibial torsion, and an enlarged fat pad with patella alta (166). Dislocation of the patella may be congenital. The dislocation occurs in flexion as a result of a faulty knee extension mechanism.

The attachment site of the quadriceps femoris to the tibia at the tibial tuberosity is another site for injury and the development of anterior pain. The tensile force of the quadriceps femoris can create tendinitis at this insertion site. This is commonly seen in athletes who do vigorous jumping, such as in volleyball, basketball, and track and field (106). In children age 8 to 15 years, a tibial tubercle epiphysitis can develop. This is referred to as Osgood-Schlatter disease. This disease is an avulsion fracture of the growing tibial tuberosity that can also avulse the epiphysis. Bony growths can develop on the site. The cause of both of these conditions is overuse of the extensor mechanism (106).

Overuse of the extensor mechanism can also cause irritation of the plica. Plica injury can also result from a direct blow, a valgus rotary force applied to the knee, or weakness in the vastus medialis oblique. The plica become thick, inelastic, and fibrous with injury, making it difficult to sit for long periods and creating pain on the superior knee (19). The medial patella may snap and catch during flexion and extension with injury to the plica.

The Ankle and Foot

The foot and ankle make up a complex anatomical structure consisting of 26 irregularly shaped bones, 30 synovial joints, more than 100 ligaments, and 30 muscles acting on the segments. All of these joints must interact harmoniously and in combination to achieve a smooth motion. Most of the motion in the foot occurs at three of the synovial joints: the talocrural, the subtalar, and the midtarsal joints (103). The foot moves in three planes, with most of the motion occurring in the rear foot.

The foot contributes significantly to the function of the whole lower limb. The foot supports the weight of the body in both standing and locomotion. The foot must be a loose adapter to uneven surfaces at contact. Also, upon contact with the ground, it serves as a shock absorber, attenuating the large forces resulting from ground contact. Late in the support phase, it must be a rigid lever for effective propulsion. Finally, when the foot is fixed during stance, it must absorb the rotation of the lower extremity. These functions of the foot all occur during a closed kinetic chain as it is receiving frictional and reaction forces from the ground or another surface (103).

The foot can be divided into three regions. The rear-foot, consisting of the talus and the calcaneus; the midfoot, including the navicular, cuneiforms, and the cuboid; and the forefoot, containing the metatarsals and the phalanges. These structures are shown in Figure 6-28.

Talocrural Joint

The proximal joint of the foot is the talocrural joint, or ankle joint (Fig. 6-28). It is a uniaxial hinge joint formed by the tibia and fibula (tibiofibular joint) and the tibia and talus (tibiotalar joint). This joint is designed for stability rather than mobility. The ankle is stable when large forces are absorbed through the limb, when stopping and turning, and in many of the lower limb movements performed on a daily basis. If any of the anatomical support structures around the ankle joint are injured, however, the joint can become very unstable (61).

The tibia and fibula form a deep socket for the trochlea of the talus, creating a mortise. The medial side of the mortise is the inner side of the medial malleolus, a projection on the distal end of the tibia. On the lateral side is the inner surface of the lateral malleolus, a distal projection on the fibula. The lateral malleolus projects more distally than the medial malleolus and protects the lateral ligaments of the ankle. It also acts as a bulwark against any lateral displacement. Because the lateral malleolus projects more distally, it is also more susceptible to fracture with an inversion sprain to the lateral ankle.

The tibia and fibula fit snugly over the trochlea of the talus, a bone that is wider anteriorly than posteriorly (75). The difference in width of the talus allows for some abduction and adduction of the foot. The close-packed position for the ankle is the dorsiflexed position when the talus is wedged in at its widest spot.

The ankle has excellent ligamentous support on the medial and lateral sides. The location and actions of the ligaments are presented in Figure 6-29. The ligaments that surround the ankle limit plantarflexion and dorsiflexion, anterior and posterior movement of the foot, tilting of the talus, and inversion and eversion (156). Each of the


lateral ligaments has a specific role in stabilizing the ankle depending on the position of the foot (64).


FIGURE 6-28 Thirty joints in the foot work in combination to produce the movements of the rear foot, midfoot, and forefoot. The subtalar and midtarsal joints contribute to pronation and supination. The intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal joints contribute to movements of the forefoot and the toes. Joints are shown from the superior (A), lateral (B), and posterior (C) view.

The stability of the ankle depends on the orientation of the ligaments, the type of loading, and the position of the ankle at the time of stress. The lateral side of the ankle joint is more susceptible to injury, accounting for 85% of ankle sprains (156).

The axis of rotation for the ankle joint is a line between the two malleoli, running oblique to the tibia and not in line with the body (33). Dorsiflexion occurs at the ankle joint as the foot moves toward the leg (e.g., when lifting the toes and forefoot off the floor) or as the leg moves toward the foot (e.g., in lowering down with the foot flat on the floor). These actions are illustrated in Figure 6-30.




FIGURE 6-29 Ligaments of the foot and ankle.

Subtalar Joint

Moving distally from the talocrural joint is the subtalar, or talocalcaneal, joint, which consists of the articulation between the talus and the calcaneus. All of the joints in the foot, including the subtalar joint, are shown in Figure 6-28. The talus and the calcaneus are the largest of the weight-bearing bones in the foot and form the hindfoot. The talus links the tibia and fibula to the foot and is called the keystone of the foot. No muscles attach to the talus. The calcaneus provides a moment arm for the Achilles tendon and must accommodate large impact loads at heel strike and high tensile forces from the gastrocnemius and soleus muscles.




FIGURE 6-30 Plantarflexion (PF) and dorsiflexion (DF) occur about a mediolateral axis running through the ankle joint. The range of motion for plantarflexion and dorsiflexion is approximately 50° and 20°, respectively. Plantarflexion and dorsiflexion can be produced with the foot moving on a fixed tibia or with the tibia moving on a fixed foot.

The talus articulates with the calcaneus at three sites, anteriorly, posteriorly, and medially, where the convex surface of the talus fits into a concave surface on the calcaneus. The subtalar joint is supported by five short and powerful ligaments that resist severe stresses in lower extremity movements. The location and action of these ligaments are presented inFigure 6-29. The ligaments that support the talus limit the motions of the subtalar joint.


FIGURE 6-31 The axis of rotation for the subtalar joint runs diagonally from the posterolateral plantar surface to the anteromedial dorsal surface. The axis is approximately 42° in the sagittal plane (top) and 16° in the transverse plane. The solid line bisects the posterior surface of the calcaneus and the distal anteromedial corner of the calcaneus; thedashed line bisects the talus.

The axis of rotation for the subtalar joint runs obliquely from the posterior lateral plantar surface to the anterior dorsal medial surface of the talus (Fig. 6-31). It is tilted vertically 41° to 45° from the horizontal axis in the sagittal plane and is slanted 16° to 23° medially from the longitudinal axis of the tibia in the frontal plane (152). Because the axis of the subtalar joint is oblique through the sagittal, frontal, and transverse planes of the foot, tri-planar motion can occur.

The triplanar movements at the subtalar joint are termed pronation and supination. Pronation, occurring in an open-chain system with the foot off the ground, consists of calcaneal eversion, abduction, and dorsiflexion (146). Eversion is the movement in the frontal plane in which the lateral border of the foot moves toward the leg in non-weight bearing or the leg moves toward the foot in weight bearing (Fig. 6-32). The transverse plane movement is abduction, or pointing the toes out. It occurs with external rotation of the foot on the leg and lateral movement of the calcaneus in the non-weight-bearing position or internal rotation of the leg with respect to the calcaneus and medial movement of the talus in weight bearing. The sagittal plane movement of dorsiflexion occurs as the calcaneus moves up on the talus in non-weight bearing or as the talus moves down on the calcaneus in weight bearing. An illustration of differences in subtalar movements between open- and closed-chain positioning is shown in Figure 6-32.

Supination is just the opposite of pronation, with calcaneal inversion, adduction, and plantarflexion in the non-weight-bearing position and calcaneal inversion and talar abduction and dorsiflexion in the weight-bearing position (102). The frontal plane movement of inversion occurs as the medial border of the foot moves toward the medial leg in non-weight bearing or as the medial aspect of the leg moves toward the medial foot in weight bearing,


as the calcaneus lies on the lateral surface. In the transverse plane, adduction, or toeing-in, occurs as the foot internally rotates on the leg in non-weight bearing, and the calcaneus moves medially or the leg externally rotates on the foot in weight bearing and the talus moves laterally. The plantarflexion movements in the sagittal plane occur as the calcaneus moves distally while non-weight bearing or as the talus moves proximally while weight bearing.


FIGURE 6-32 Top. With the foot off the ground, the foot moves on a fixed tibia, and the subtalar movement of pronation is produced by eversion, abduction, and dorsiflex-ion. Supination in the open chain is produced by inversion, adduction, and plantarflexion. Bottom. In a closed kinetic chain with the foot on the ground, much of the pronation and supination are produced by the weight of the body acting on the talus. In this weight-bearing position, the tibia moves on the talus to produce pronation and supination.

The prime function of the subtalar joint is to absorb the rotation of the lower extremity during the support phase of gait. With the foot fixed on the surface and the femur and tibia rotating internally at the beginning of stance and externally at the end of stance, the subtalar joint absorbs the rotation through the opposite actions of pronation and supination (72). Pronation is a combination of dorsiflexion, abduction, and eversion, and supination is a combination of plantarflexion, adduction, and inversion. The subtalar joint absorbs rotation by acting as a mitered hinge, allowing the tibia to rotate on a weight-bearing foot (160). Inversion and eversion are also used as corrective motions in postural adjustments to keep the foot stable under the center of gravity (160).

A second function of the subtalar joint is shock absorption. This may also be accomplished by pronation. The subtalar movements also allow the tibia to rotate internally faster than the femur, facilitating unlocking at the knee joint.

Midtarsal Joint

Of the remaining articulations in the foot, the midtarsal, or transverse tarsal, joint has the greatest functional significance (Fig. 6-28). It actually consists of two joints, thecalcaneocuboid joint on the lateral side and the talonavicular joint on the medial side of the foot. In combination, they form an S-shaped joint with two axes, oblique and longitudinal (152). Five ligaments support this region of the foot (see Fig. 6-29). Motion at these two joints contributes to the inversion and eversion, abduction and adduction, and dorsiflexion and plantarflexion at the subtalar and ankle joints.

Movement at the midtarsal joint depends on the subtalar joint position. When the subtalar joint is in pronation, the two axes of the midtarsal joint are parallel, which unlocks the joint, creating hypermobility in the foot (119).


This allows the foot to be very mobile in absorbing the shock of contact with the ground and also in adapting to uneven surfaces. When the axes are parallel, the forefoot is also allowed to flex freely and extend with respect to the rear foot. The motion at the midtarsal joint is unrestricted from heel strike to foot flat as the foot bends toward the surface.

During supination of the subtalar joint, the two axes run through the midtarsal joint converge. This locks in the joint, creating rigidity in the foot necessary for efficient force application during the later stages of stance (119). The midtarsal joint becomes rigid and more stable from foot flat to toe-off in gait as the foot supinates. It is usually stabilized, creating a rigid lever, at 70% of the stance phase (102). At this time, there is also a greater load on the midtarsal joint, making the articulation between the talus and the navicular more stable. Figure 6-33 depicts these actions.

Other Articulations of the Foot

The other articulations in the midfoot, the inter tarsal articulations, between the cuneiforms and the navicular and cuboid and intercuneiform, are gliding joints (Fig. 6-28). At the articulation between the cuneiforms and the navicular and cuboid, small amounts of gliding and rotation are allowed (75).

At the intercuneiform articulations, a small vertical movement takes place, thus altering the shape of the transverse arch in the foot (38). These joints are supported by stronginterosseous ligaments.

The forefoot consists of the metatarsals and the phalanges and the joints between them. The function of the forefoot is to maintain the transverse metatarsal arch, maintain the medial longitudinal arch, and maintain the flexibility in the first metatarsal. The plane of the forefoot at the metatarsal head is formed by the second, third, and fourth metatarsals. This plane is perpendicular to the vertical axis of the heel in normal forefoot alignment. This is the neutral position for the forefoot (Fig. 6-34). If the plane is tilted so that the medial side lifts, it is termed forefoot supination or varus (72). If the medial side drops below the neutral plane, it is termed forefoot pronation or valgus. Forefoot valgus is not as common as forefoot varus (Fig. 6-34). Also, if the first metatarsal is below the plane of the adjacent metatarsal heads, it is considered to be a plantarflexed first ray and is commonly associated with high-arched feet (72).


FIGURE 6-33 The midtarsal joints consist of the articulations between the calcaneus and the cuboid (calcaneocuboid joint) and the talus and the navicular (talonavicular joint). Each joint has an axis of rotation that runs obliquely across the joint. When the two axes are parallel to each other, the foot is flexible and can freely move. If the axes do not run parallel to each other, the foot is locked in a rigid position. This occurs with supination.

The base of the metatarsals is wedge shaped, forming a mediolateral or transverse arch across the foot. The tarsometatarsal articulations are gliding or planar joints allowing limited motion between the cuneiforms and the first, second, and third metatarsals and the cuboid and the fourth and fifth metatarsals (75).

The tarsometatarsal joint movements change the shape of the arch. When the first metatarsal flexes and abducts as the fifth metatarsal flexes and adducts, the arch deepens, or increases in curvature. Likewise, if the first metatarsal extends and adducts and the fifth metatarsal extends and abducts, the arch flattens.

Flexion and extension at the tarsometatarsal articulations also contribute to inversion and eversion of the foot. Greater movement is allowed between the first metatarsal and the first cuneiform than between the second metatarsal and the cuneiforms (102). Mobility is an important factor in the first metatarsal because it is significantly involved in weight bearing and propulsion. The limited mobility at the second metatarsal is also significant because it is the peak of the plantar arch and a continuation of the long axis of the foot. The tarsometatarsal joints are supported by the medial and lateral dorsal ligaments.

The metatarsophalangeal joints are biaxial, allowing both flexion and extension and abduction and adduction (Fig. 6-28). These joints are loaded during the propulsive phase of gait after heel-off and the initiation of plantar flexion and phalangeal flexion (61). Two sesamoid bones lie under the first metatarsal and reduce the load on one of the hallucis muscles in the propulsive phase. The movements at the metatarsophalangeal joints are similar to those seen in the same joints in the hand except that greater extension occurs in the foot as a result of requirements for the propulsive phase of gait.

The interphalangeal joints are similar to those found in the hand (Fig. 6-28). These uniaxial hinge joints allow for flexion and extension of the toes. The toes are much smaller than the fingers. They are also less developed, probably because of continual wearing of shoes (75). The toes are less functional than the fingers because they lack an opposable structure like the thumb.

Arches of the Foot

The tarsals and metatarsals of the foot form three arches, two running longitudinally and one running transversely across the foot. This creates an elastic shock-absorbing


system. In standing, half of the weight is borne by the heel and half by the metatarsals. One third of the weight borne by the metatarsals is on the first metatarsal, and the remaining load is on the other metatarsal heads (61). The arches form a concave surface that is a quarter of a sphere (75). The arches are shown in Figure 6-35.


FIGURE 6-34 The metatarsal head should be perpendicular to the heel in a normal alignment in the foot. There are many variations in this alignment, including forefoot valgus (B), in which the medial side of the forefoot drops below the neutral plane; forefoot varus (A), in which the medial side lifts; and rear foot varus (C), in which the calcaneus is inverted. In weight bearing, these alignments occur with different movements.

The lateral longitudinal arch is formed by the calcaneus, cuboid, and fourth and fifth metatarsals. It is relatively flat and limited in mobility (61). Because it is lower than the medial arch, it may make contact with the ground and bear some of the weight in locomotion, thus playing a support role in the foot.

The more dynamic medial longitudinal arch runs across the calcaneus to the talus, navicular, cuneiforms, and first three metatarsals. It is much more flexible and mobile than the lateral arch and plays a significant role in shock absorption upon contact with the ground. At heel strike, part of the initial force is attenuated by compression of a fat pad positioned on the inferior surface of the calcaneus. This is followed by a rapid elongation of the medial arch that continues to maximum elongation at toe contact with the ground. The medial arch shortens at midsupport and then slightly elongates and again rapidly shortens at toe-off (61). Flexion at the transverse tarsal and tarsometatarsal joints increases the height of the longitudinal arch as the metatarsophalangeal joints extend at pushoff (147). The movement of the medial arch is important because it dampens impact by transmitting the vertical load through deflection of the arch.

Even though the medial arch is very adjustable, it usually does not make contact with the ground unless a person has functional flat feet. The medial arch is supported by the keystone navicular bone, the calcaneonavicular ligament, the long plantar ligament, and the plantar fascia (38,62).

The plantar fascia, illustrated in Figure 6-36, is a strong, fibrous plantar aponeurosis running from the calcaneus to the metatarsophalangeal articulation. It supports both arches and protects the underlying neurovascular bundles. The plantar fascia can be irritated as a result of ankle motion through extreme ranges of motion because the


arch is flattened in dorsiflexion and increased in plantar flexion. These actions place a wide range of tensions on the fascial attachments (38). Also, if the plantar fascia is short, the arch is likely to be higher.


FIGURE 6-35 Three arches are formed by the tarsals and metatarsals: the transverse arches (A), which support a significant portion of the body weight during weight bearing; the medial longitudinal arch (B), which dynamically contributes to shock absorption; and the lateral longitudinal arch (C), which participates in a support role function during weight bearing.


FIGURE 6-36 The plantar fascia is a strong fibrous aponeurosis that runs from the calcaneus to the base of the phalanges. It supports the arches and protects structures in the foot.

The transverse arch is formed by the wedging of the tarsals and the base of the metatarsals. The bones act as beams for support of this arch, which flattens with weight bearing and can support three to four times body weight (152). The flattening of this arch causes the forefoot to spread considerably in a shoe, indicating the importance of sufficient room in shoes to allow for this spread.

Individuals can be classified according to the height of the medial arch into foot types that are normal, high-arched or pes cavus, and flat-footed or pes planus. They can be further classified as being rigid or flexible. The midfoot of the high-arched rigid foot does not make any contact with the ground and usually has little or no inversion or eversion in stance. It is a foot type that has poor shock absorption. The flat foot, on the other hand, is usually hypermobile, with most of the plantar surface making contact in stance. This weakens the medial side. It is a foot type usually associated with excessive pronation throughout the support phase of gait.

Movement Characteristics

The Range of Motion At The Ankle Joint Varies With The Application of Loads To The Joint. The Range of Motion In Dorsiflexion Is Limited By The Bony Contact Between The Neck of the Talus and The Tibia, The Capsule and Ligaments, and The Plantar Flexor Muscles. The Average Range of Dorsiflexion Is 20°, Although Approximately 10° of Dorsiflexion Is Required For Efficient Gait (24). More Dorsiflexion Can Be Attained Up Through 40° Plus When Performing A Full Squat Movement Using Body Weight. Healthy Elderly Individuals Typically Exhibit Less Passive Dorsiflexion Range of Motion But More Dorsiflexion In Gait Than Their Younger Counterparts.

Any arthritic condition in the ankle also reduces passive and increases active dorsiflexion range of motion. The


increase in dorsiflexion in the arthritic joint is primarily because of a decrease in flexibility in the gastrocnemius or a weakness in the soleus. With the maintenance of the knee flexion angle during the support period of gait, a collapse into greater dorsiflexion is observed (89). With increased dorsiflexion and knee flexion, more weight is maintained on the heel.

Plantarflexion is movement of the foot away from the leg (e.g., rising up on the toes) or moving the leg away from the foot (such as in leaning back, away from the front of the foot) (Fig. 6-30). Plantarflexion is limited by the talus and the tibia, the ligaments and the capsule, and the dorsiflexor muscles. The average range of motion for plantarflexion is 50°, with 20° to 25° of plantarflexion used in gait (24,29,109).

In an arthritic or pathological gait, plantarflexion range of motion is less for both passive and active measurements. The reduction of plantarflexion in gait is substantial because of weak calf muscles. Healthy elderly people do not demonstrate substantial loss in either passive or active plantarflexion range of motion (89).

In the rear foot, subtalar eversion and inversion can be measured by the angle formed between the leg and the calcaneus. In the closed-chain weight-bearing movement, the talus moves on the calcaneus, and in the open chain, the calcaneus moves on the talus. Calcaneal inversion and eversion are the same regardless of weight-bearing or open-chain motion. This makes calcaneal inversion and eversion measurements very useful in quantifying subtalar motion (Fig. 6-32). Subtalar inversion is possible through 20° to 32° of motion in young healthy individuals and 18° in healthy elderly individuals (89,105). Inversion is greatly reduced in individuals with osteoarthritis in the ankle joint. Eversion, measured passively, averages 5° and 4° for healthy young and elderly individuals, respectively (89). In 84% of arthritic patients, excessive calcaneal eversion creates what is known as a hindfoot valgus deformity.

Combined Movements of the Knee and Ankle/Subtalar

Movements at the knee and foot need to be coordinated to maximize absorption of forces and minimize strain in the lower extremity linkage. For example, during the support phase of gait, pronation and supination in the foot should correspond with rotation at the knee and hip. At heel strike, the foot typically makes contact with the ground in a slightly supinated position, and the foot is lowered to the ground in plantarflexion (39). The subtalar joint begins to immediately pronate, accompanying internal rotation and flexion at the knee and hip joints (62). The talus rotates medially on the calcaneus, initiating pronation as a result of lateral heel strike and putting stress on the medial side (140). Pronation continues until it reaches a maximum at approximately 35% to 50% of the stance phase (9,155), and this corresponds to the achievement of maximum flexion and internal rotation at the knee.

At the stage of foot flat in stance, the knee joint begins to externally rotate and extend, and because the forefoot is still fixed on the ground, these movements are transmitted to the talus (62). The subtalar joint should begin to supinate in response to the external rotation and extension that occurs up through heel-off. Many injuries of the lower extremity are thought to be associated with a lack of synchrony between these movements at the knee and subtalar joint.

Excessive pronation has been speculated to be a major cause of injury, but it is not necessarily the maximum degree of pronation but rather the percentage of support in which pronation is present and the synchronization with the knee joint movements. Pronation can be present for as much as 55% to 85% of stance, creating problems when the lower limb moves into external rotation and extension as the subtalar joint is still pronating (104). The lack of synchrony between the subtalar and knee joint motions has been shown to increase with increasing velocities (155) and increases in stride length (154).

Alignment and Foot Function

Foot function can be altered significantly with any variation in alignment in the lower extremity or as a result of abnormal motion in the lower extremity linkage. Typically, any varum alignment in the lower extremity increases the pronation at the subtalar joint in stance (67). A Q-angle at the knee greater than 20°, tibial varum greater than 5°, rear foot varum (calcaneus inversion) greater than 2°, and forefoot varum (forefoot adduction) greater than 3° are all deemed to be significant enough to produce an increase in subtalar pronation (89).

Rear foot varus is usually a combination of subtalar varus and tibial varum in which the calcaneus inverts and the lower third of the tibia deviates in the direction of inversion. Forefoot varus, the most common cause of excessive pronation, is the inversion of the forefoot on the rear foot with the subtalar joint in the neutral position (24). It is caused by the inability of the talus to derotate, leaving the foot pronated at heel lift and preventing any supination. This shifts the body weight to the medial side of the foot, creating a hypermobile midtarsal joint and an unstable first metatarsal.

Both rear foot and forefoot varus double the amount of pronation in midstance compared with normal foot function and continue pronation into late stance (67). In some cases, the pronation continues until the very end of the support period. This is a major injury-producing mechanism because the continued pronation is contrary to the external rotation being produced in the leg. It is the primary cause of discomfort and dysfunction in the foot and leg. The transverse rotation being produced by the hypermobile foot, still in pronation late in stance, is absorbed at the knee joint and can create lateral hip pain through an anterior tilt of the pelvis or strain the invertor muscles (39).



A plantarflexed first ray can also produce excessive pronation (67). The first ray is usually plantarflexed by the pull of the peroneus longus muscle and is commonly seen in both rear foot and forefoot varus alignments. This alignment causes the medial side of the foot to load prematurely, with greater than normal loads limiting forefoot inversion and creating supination in midstance. However, sudden pronation is generated at heel-off, developing high shear forces across the forefoot, especially at the first and fifth metatarsals (67).

Hypermobility of the first ray is generated because the peroneus longus muscle cannot stabilize the first metatarsal. During pronation, the medial side is hypermo-bile, placing a large load and shear force on the second metatarsal. This is a common cause of stress fracture of the second metatarsal and subluxation of the first metatarsophalangeal joint (1,24).

Although it is not common, a person may have a forefoot valgus alignment. This may be caused by a bony deformity in which the plantar surfaces of the metatarsals evert relative to the calcaneus with the subtalar joint in the neutral position (24). Forefoot valgus causes the forefoot to be prematurely loaded in gait, creating supination at the subtalar joint. This alignment is typically seen in high-arched feet.

Foot type, as mentioned previously, can also affect the amount of pronation or supination. In the normal foot with a subtalar axis of 42° to 45°, the internal rotation of the leg is equal to the internal rotation of the foot (70). In a high-arched foot, the axis of the subtalar joint is more vertical and is greater than 45°, so that for any given internal rotation of the leg, there is less internal rotation of the foot, creating less pronation for any given leg rotation.

In the flat foot, the subtalar joint axis is less than 45°, that is, closer to the horizontal. This has the opposite effect to an axis that is greater than 45°. Thus, for any given internal rotation of the leg, there is greater internal rotation of the foot, creating greater pronation (70).

A final alignment consideration is the equine foot, in which the Achilles tendon is short, creating a significant limitation of dorsiflexion in gait. The equinus deviation can be reproduced with a tight and inflexible gastrocnemius and soleus. Because the tibia is unable to move forward on the talus in midsupport, the talus moves anteriorly and pronates excessively to compensate (39). An early heel rise and toe walking are symptoms of this disorder.

Muscle Actions

Twenty-three muscles act on the ankle and the foot, 12 originating outside the foot and 11 inside the foot. All of the 12 extrinsic muscles, except for the gastrocnemius, soleus, and plantaris, act across both the subtalar and mid-tarsal joints (50). The insertion, actions, and nerve supply of all of these muscles are presented in Figure 6-37.

The muscles of the foot play an important role in sustaining impacts of very high magnitude. They also generate and absorb energy during movement. The ligaments and tendons of the muscles store some of the energy for later return. For example, the Achilles tendon can store 37 joules (J) of elastic energy, and the ligaments of the arch can store 17 J as the foot absorbs the forces and body weight (142).

Plantarflexion is used to propel the body forward and upward, contributing significantly to the other propelling forces generated in heel-off and toe-off Plantar flexor muscles are also used eccentrically to slow down a rapidly dorsiflexing foot or to assist in the control of the forward movement of the body, specifically the forward rotation of the tibia over the foot.

Plantarflexion is a powerful action created by muscles that insert posterior to the transverse axis running through the ankle joint. The majority of the plantarflexion force is produced by the gastrocnemius and the soleus, which together are referred to as the triceps surae muscle group. Because the gastrocnemius also crosses the knee joint and can act as a knee flexor, it is more effective as a plantar flexor with the knee extended and the quadriceps femoris activated.

In a sprint racing start, the gastrocnemius is maximally activated with the knee extended and the foot placed in full dorsiflexion. The soleus, called the workhorse of plantarflexion, is flatter than the gastrocnemius (38). It is also the predominant plantarflexor during a standing posture. A tight soleus can create a functional short leg, often seen in the left leg of people who drive a car a great deal. As explained in an earlier section, an inflexible or tight soleus limits dorsiflexion and facilitates compensatory pronation that creates the functionally shorter limb.

The action of these plantarflexor muscles is mediated through a stiff subtalar joint, allowing for an efficient transfer of the muscular force. The gastrocnemius and possibly the soleus have also been shown to produce supination when the forefoot is on the floor during the later stages of the stance phase of gait. Plantarflexion is usually accompanied by both supination and adduction.

The other plantar flexor muscles produce only 7% of the remaining plantarflexor force (38). Of these, the peroneus longus and the peroneus brevis are the most significant, with minimal plantarflexor contribution from the plantaris, flexor hallucis longus, flexor digitorum longus, and tibialis posterior. The plantaris is an interesting muscle, similar to the palmaris longus in the hand, in that it is absent in some individuals, very small in others, and well developed in yet others. Overall, its contribution is usually insignificant.

Dorsiflexion at the ankle is actively used in the swing phase of gait to help the foot clear the ground and in the stance phase of gait to control lowering of the foot to the floor after heel strike. Dorsiflexion is also present in the middle part of the stance phase as the body lowers and the tibia travels over the foot, but this action is controlled eccentrically by the plantarflexor muscles (46). The dorsiflexor muscles are those that insert anterior to the transverse axis running through the ankle (50) (see Fig. 6-37).






FIGURE 6-37 Muscles acting on the ankle joint and foot, including superficial posterior muscles (A) and surface anatomy (B) of posterior lower leg; deep posterior muscles of the lower leg (C), muscles (D) and surface anatomy of the lower leg (E); anterior muscle (F) and surface anatomy (G); surface anatomy of the foot and ankle (H); and muscles in the dorsal (I, J, K) and ventral (L) surface of the foot.



The most medial dorsiflexor is the tibialis anterior, whose tendon is farthest from the joint, thus giving it a significant mechanical advantage and making it the most powerful dorsiflexor (38). The tibialis anterior has a long tendon that begins halfway down the leg. It is also the largest muscle and provides additional support to the medial longitudinal arch. Assisting the tibialis anterior in dorsiflexion are the extensor digitorum longus and the extensor hallucis longus. These muscles pull the toes up in extension. The peroneus tertius also contributes to the dorsiflexion force.

Eversion is created primarily by the peroneal muscle group. These muscles lie lateral to the long axis of the tibia. They are known as pronators in the non-weight-bearing position because they evert the calcaneus and abduct the forefoot. The peroneus longus is an everter that is also responsible for controlling the pressure on the first metatarsal and some of the finer movements of the first metatarsal and big toe, or hallux.

The lack of stabilization of the first metatarsal by the peroneus longus leads to hypermobility of the medial side of the foot. The peroneus brevis also contributes through the production of eversion and forefoot abduction, and the peroneus tertius contributes through dorsiflexion and eversion. Both the peroneus tertius and peroneus brevis stabilize the lateral aspect of the foot. Pronation in the weight-bearing position is primarily generated by weight bearing on the lateral side of the foot in heel strike. This drives the talus medially, producing pronation. Figure 6-38 shows how pronation is produced through weight bearing.

The inverters of the foot are the muscles lying medial to the long axis of the tibia. These muscles generate inversion of the calcaneus and adduction of the forefoot (38).


FIGURE 6-38 When the heel strikes the ground on the lateral (L) aspect, a vertical force is directed on the outside of the foot. The force of body weight is acting down through the ankle joint. Because these two forces do not line up, the talus is driven medially (M), producing the pronation movement.

Inversion is created primarily by the tibialis anterior and the tibialis posterior, with assistance from the toe flexors, flexor digitorum longus, and flexor hallucis longus. The extensor hallucis longus works with the flexor hallucis longus to adduct the forefoot during inversion.

The intrinsic muscles of the foot work as a group and are very active in the support phase of stance. They basically follow supination and are more active in the later portions of stance to stabilize the foot in propulsion (70). In a foot that excessively pronates, they are also more active as they work to stabilize the midtarsal and subtalar joints. There are 11 intrinsic muscles, and 10 of these are on the plantar surface arranged in four layers. Figure 6-37 has a full listing of these muscles.

Strength of the Ankle and Foot Muscles

The strongest movement at the ankle or foot is plantarflexion. This is because of the larger muscle mass contributing to the movement. It is also related to the fact that the plantarflexors are used more to work against gravity and maintain an upright posture, control lowering to the ground, and add to propulsion. Even standing, the plantarflexors, specifically the soleus, contract to control dorsiflexion in the standing posture.

Plantarflexion strength is greatest from a position of slight dorsiflexion. A starting dorsiflexion angle of 105° increases plantarflexion strength by 16% from the neutral 90° position. Plantarflexion strength measured from 75° and 60° of plantarflexion is reduced by 27% and 42%, respectively compared with strength measured in the neutral position (152). Additionally, plantarflexion strength can be increased if the knee is maintained in an extended position, placing the gastrocnemius at a more advantageous muscle length.

Dorsiflexion is incapable of generating a large force because of its reduced muscle mass and because it is minimally used in daily activities. The strength of the dorsiflexor muscles is only about 25% that of the plantarflexor muscles (152). Dorsiflexion strength can be enhanced by placing the foot in a few degrees of plantarflexion before initiating dorsiflexion.

Conditioning of the Foot and Ankle Muscles

Both stretching and strengthening exercises for selected movements at the foot and ankle are presented in Figure 6-39. The plantarflexor muscles are exercised to a great extent in daily living activities: They are used to walk, get out of chairs, go up stairs, and drive a car. Strengthening the plantarflexors by using resistive exercises is also relatively easy. Any heel-raising exercise offers a significant amount of resistance because body weight is lifted by this muscle group. With the weight centered over the foot, the leverage of the plantarflexors is very efficient for handling




large loads; thus, a heel-raise activity with weight on the shoulders can usually be done with a considerable amount of weight. This exercise is perfect for the gastrocnemius because the strength of this muscle is enhanced with the knee extended and the quadriceps femoris contracting.


FIGURE 6-39 Sample stretching and strengthening exercises for selected muscle groups are illustrated.

To specifically strengthen the soleus, a seated position is best. This position flexes the knee and reduces the contribution of the gastrocnemius significantly. Weight or resistance can be placed on the thigh as plantarflexion is produced.

It is important to maintain flexibility in the plantarflexors because any inflexibility in this muscle group can create an early heel raise and excessive pronation in gait. Inflexibility in the plantarflexors is common in women who wear high heels much of the time (75). In fact, both men and women are susceptible to strain in the plantarflexors when going from a higher heel to a lower heel in either exercise or activities of daily living. It is better to maintain the flexibility in the muscle group through stretching with the knee extended and the ankle in maximum dorsiflexion.

Flexibility in the gastrocnemius and the soleus can be somewhat isolated. Flexibility of the gastrocnemius can best be tested with the knee extended, and flexibility of the soleus is best tested with the knees flexed to 35°.

The strength of the dorsiflexors is limited, but it should be maintained so that fatigue does not set in during a long walk or run. Fatigue in the muscle group leads to foot drop in swing and slapping of the foot on the surface following heel strike. To strengthen the muscle group, a seated position works best so that resistance can be applied below the foot with sandbags, weights, or surgical tubing (Fig. 6-39). Also, ankle machines are available that allow a full range of dorsiflexion and high-resistance training of this movement. Flexibility of dorsiflexion can also be best achieved in the seated position through maximum plantarflexion activities.

Strength and flexibility of the inverters and everters of the ankle are important for athletes participating in activities in which ankle injuries are common. This includes basketball, volleyball, football, soccer, tennis, and a wide variety of other activities. Stretching and strengthening the inversion and eversion muscles can be done with the foot flat on the floor on a towel or attached to surgical tubing. Weight can be put on the towel, which can then be pulled toward the foot in either inversion or eversion depending on which side of the weights the foot is placed. Circumduction and figure-eight tracing are good flexibility exercises.

The intrinsic muscles of the foot are usually atrophied and weak because we regularly wear shoes. Because the intrinsic muscles support the arch of the foot and stabilize the foot during the propulsive phase of gait, it is worthwhile to give these muscles some conditioning. The best way to exercise the intrinsic muscle group as a whole is to forego shoes and go barefoot. The movement potential of the foot is best illustrated by individuals who have upper extremity disabilities and must use their feet to perform daily functions. These individuals can become very versatile and adept at using the feet to perform a wide range of functions.

During walking or running, impact is the same either with shoes or barefoot; it is the manner in which the forces are absorbed that is different between the two. With a shoe, the foot is more rigid during the shock absorption phase of support and depends on the shoe for support and protection. During shock absorption in barefoot gait, the foot is more mobile, with more arch deflection upon loading (138). This does not necessarily mean that shoes should not be worn–the injury rate in barefoot running would initially be high because of the significant change imposed by removing the shoes. There is also a danger associated with barefoot activity and the possibility of injury from sharp objects. Going barefoot in the summer, however, is one way of improving the condition of the intrinsic muscles.

Attesting to the benefits of barefoot activity is the low injury rate in populations that remain largely barefoot. The incidence of injury to barefoot runners is much lower than among the shod population (138). Finally, the intrinsic musculature in a person with a flat mobile foot is much more developed than in a person with a high-arched, rigid foot because of the difference in movement characteristics in loading of the foot.

Injury Potential of the Ankle and Foot

Injuries to the foot and ankle account for a large portion of the injuries to the lower extremity. In some sports or activities, such as basketball, the ankle joint is the most frequently injured part of the lower extremity. Whereas injuries to the hindfoot usually occur as a result of vertical compression, injuries to the midfoot occur with excessive lateral movement or range of motion in the foot (38). Injuries to the forefoot occur similarly to injuries in long bones elsewhere in the body. In this area of the foot, both compressive and tensile forces create the injury.

Most injuries to the ankle joint and the foot occur as a result of overtraining or an excessive training bout. The ankle joint is injured frequently in activities such as running, during which the foot is loaded suddenly and repeatedly (138). Foot and ankle injuries are also associated with anatomical factors; a greater incidence of injury is seen in individuals who overpronate and in those with cavus alignment in the lower extremity. Functional ankle instability can also be related to a number of factors, including peroneal tendon weakness, rotational talar instability, subtalar instability, tibiofibular instability, or hind-foot misalignment (64).

One of the most common injuries to the foot is ankle sprain. Sprains most commonly occur in the lateral complex of the ankle during inversion. The mechanism of injury is a movement of the tibia laterally, posteriorly, anteriorly, or


rotating while the foot is firmly fixed on the surface. Stepping into a hole in the ground, walking off a curb, or losing one's balance in high heels are other instances in which the ankle can be sprained. The factors associated with ankle sprain differ between men and women. Women with increased tibial varum and calcaneal eversion range of motion and men with increased talar tilt are more susceptible to ankle ligament injury (17).

Most ankle sprains in athletes are seen during the cutting maneuver, when the cut is made with the foot opposite to the direction of the run (50) or when landing on another player's foot. For example, the left foot is sprained as it drives in plantarflexion and inversion to the right. The plantarflexion and inversion action is the cause of sprain to the lateral ligamentous structure, with the anterior talofibular ligament most likely to be sprained (69). If the cut is made with greater foot inversion, the calcaneofibu-lar ligament is the next ligament that may be damaged (69). The injury is created with a talar tilt as the talus moves forward out of the ankle mortise. Any talar tilt greater than 5° will likely cause ligament damage to the lateral ankle (42). With injury to the lateral ankle complex, an anterior subluxation of the talus and talar tilt may occur, creating great instability in the ankle and foot complex.

The medial ligaments of the ankle are not often sprained because of the support of the strong deltoid ligament and the bulwark created by the longer lateral malleolus. The powerful deltoid ligament can be sprained if the foot is planted and pronated and incurs a blow on the lateral side of the leg.

Although not at the ankle, the ligaments holding the tibiofibular joint together can be sprained with a forceful external rotation and dorsiflexion or a forceful inversion or eversion. The talus pushes the tibia and fibula apart, spraining the ligaments.

Many other soft tissue injuries to the foot and ankle are typically associated with overuse or some other functional malalignment. Posterior or medial tibial syndrome, previously referred to as shin splints, generates pain above the medial malleolus (72). This condition usually involves the insertion site of the tibialis posterior and can be tendinitis of the tibialis posterior tendon. It may also be periostitis, in which the insertion of the tibialis posterior pulls on the interosseous membrane and periosteum on the bone, causing an inflammation. This muscle is usually irritated through excessive pronation, which places a great deal of tension and stretch on the muscle. Lateral tibial syndrome causes pain on the anterior lateral aspect of the leg and is an overuse condition similar to that of the tibialis anterior muscle.

The Achilles tendon is another frequently strained area of the foot that can be injured as a result of overtraining. A tight Achilles tendon can also lead to a number of conditions, including pain in the calf, heel, lateral or medial ankle, and plantar surface. Multiple vigorous contractions of the gastrocnemius that overstretch the muscle group, as in hill running or in moving to a low-heel shoe from a higher heel, may strain this tendon (12). The Achilles tendon can also be irritated if there is loss of absorption in the heel pad on the calcaneus. This creates a higher amplitude shock at heel strike during locomotion that is compensated for by an increase in soleus activity. The increased muscle activity produces a corresponding increase in the loading on the Achilles tendon. Achilles tendinitis can be very painful and difficult to heal because immobilization of the area is difficult. The Achilles tendon can also rupture as a result of a vigorous muscle contraction. For example, a vigorous forward push-off after a move backward can rupture a tendon. Another method of rupture is by stepping into a hole or off a curb.

A condition that mimics the pain associated with Achilles tendinitis is retrocalcaneal bursitis. This is an inflammation of the bursae lying superior to the Achilles attachment. It is generally caused by ill-fitting shoes (12).

Plantar fasciitis, an inflammation of the plantar fascia on the underside of the foot, is another common soft tissue injury to the foot (138). Irritation usually develops on the medial plantar fascial attachment to the calcaneus and may be caused by training adjustments that increase hill running or mileage. It may also be caused by stepping into a hole or off a curb. Plantar fasciitis is most prevalent in high-arched foot types and in individuals with a tight Achilles tendon or leg length discrepancy (79). More tension placed on the plantar fascia in pronation predisposes this area to this type of injury. The plantar fascia can rupture with forceful plantarflexion, such as is seen in descending stairs or during rapid acceleration.

At the site of the irritation of the plantar fascia on the calcaneus, adolescents can develop a calcaneal apophysitis, an irritation at the site of the epiphysis of the calcaneus (79). Adults may develop a similar irritation at the same site, where heel bone spurs develop in response to the pull of the plantar fascia.

Although osteoarthritis at the ankle joint occurs at a lower incidence than that seen at the hip or knee, it can be seen in younger patients (161). This is different than the degenerative arthritis commonly seen at the hip and knee joint. Recurring injury to the ankle ligaments or a single severe ankle sprain are predisposing factors for the development of ankle osteoarthritis.

Forefoot pain can be related to conditions such as metatarsal stress fractures, metatarsalgia, and Morton's neuroma. Strain to the metatarsals, referred to as metatarsalgia, creates a dull burning sensation in the forefoot. Morton's neuroma is an inflammation of a nerve, usually between the third and fourth metatarsals at the balls of the feet. Symptoms include sharp pain, burning, or numbness. Irritation to the ligaments or soft tissue in the forefoot is usually associated with running on a hard surface. Injuries to the metatarsal are more prevalent in overpronating feet.

Nerve compression can occur at various sites in the leg and foot. Anterior compartment syndrome is a case in which nerve and vascular compression occur as a


result of hypertrophy in the anterior tibial muscles. The muscles hypertrophy to the point that they impinge on the nerves and blood vessels in the muscle compartment. Impingement can create tingling sensations or atrophy in the foot.

Injury to the osseous components of the foot typically occurs with overuse or pathological function. Metatarsal fractures are typically found in the middle of the shaft of the second or third metatarsal. This fracture is associated with tight dorsiflexor muscles or forefoot varus. A stress fracture can also develop in the metatarsals on the lateral side of the foot as a result of a tight gastrocnemius. The tight gastrocnemius prevents dorsiflexion in gait, creating compensatory pronation, an unlocked subtalar joint, and more flexibility in the first metatarsal, with the lateral metatarsal absorbing the force. A person who lacks sufficient dorsiflexion in gait is almost five times more likely than usual to acquire a stress fracture.

Fractures to the metatarsals occur with a fall on the foot, avulsion by a muscle such as the site of the attachment of the peroneus brevis on the fifth metatarsal, or as a consequence of compression. Fractures have also been associated with loss of heel pad compressive ability, requiring greater force absorption by the foot. An example of a compression injury is a fracture of the tibia or talus on the medial side that accompanies a lateral ankle sprain. This jamming of the inner ankle can also loosen bony fragments, a condition known as osteochondritis dissecans. An osteochondral fracture of the talus is a shearing type of fracture that occurs with a dorsiflexion-eversion action of the foot in which the talus impinges on the fibula during a crouch.

Contribution of Lower Extremity Musculature to Sport Skills or Movements

The lower extremity is involved primarily with weight bearing, walking, posture, and most gross motor activities. This section summarizes the lower extremity muscular contribution to a sample of movements. A more thorough review of muscular activity is provided for walking and cycling. These are examples of a functional anatomy description of a movement derived from electromyographic research.

Very few movements or sport skills do not require the use and contribution of the lower extremity muscles. For example, in landing from a jump or other airborne event, the weight of the body is decelerated over the lower extremity using the trunk, hip, and lower leg muscles (54). In a cut maneuver, the gluteus medius and the sartorius modify the foot position in the air through internal and external rotation of the hip, and in the stance phase of the cutting action, there is increased force from the gastrocnemius and the quadriceps muscles to generate more force for the change in direction (134).

Stair Ascent and Descent

Going up a flight of stairs is first initiated with a limb lift via vigorous contraction of the iliopsoas, which pulls the limb up against gravity to the next stair (99) (Fig. 6-40). The rectus femoris becomes active in this phase as it assists in the thigh flexion and eccentrically slows the knee flexion. Next, the foot is placed on the next step. At this point, there is activity in the hamstrings, primarily working to slow down the extension at the knee joint (99). As the foot makes contact with the next step, weight acceptance involves some activity in the extensors of the thigh. The next phase is pull-up, in which the limb placed on the upper step is extended to bring the body up to that step. Most of the extension is generated at the knee joint by the quadriceps. The lower leg moves posteriorly via plan-tarflexion at the ankle to increase the vertical position and the primary ankle muscle producing this motion is the soleus, with some contribution from the gastrocnemius. There is minimal contribution from the hip other than contraction by the gluteus medius to pull up the trunk over the limb (99). Finally, in the forward propelling stage in which the limb on the lower step pushes up to the next step, there is minimal activity at the hip, with the ankle joint generating the most of the force. The greatest ankle power is generated in this phase as the individual continues on to the next step. At this point, the ankle pushes off, with the plantarflexors active as the body is pushed up to the next step (99).


FIGURE 6-40 In stair ascent with the left limb leading, there is significant contribution from the quadriceps, with assistance from the plantarflexors and the iliopsoas. In descent with the right limb leading, the same muscles control the movement eccentrically. For stair climbing as a whole, there is less contribution from the hip muscles than in walking or running.



Going downstairs, or descent, requires minimal hip muscular activity. In the limb pull phase, the hip flexors are active, followed by hamstring activity in the foot placement phase, when the limb is lowered to the step surface (99). As the limb makes contact with the next step in weight acceptance, the hip is minimally involved because most of the weight is eccentrically absorbed at the knee and ankle joints. The muscles acting at the knee joint are primarily responsible for generating the forces in the forward propelling phase. The plantarflexor muscles act eccentrically to absorb foot-surface contact (52,101). There is also co-contraction of the soleus and the tibialis anterior muscles early in the absorption phase to stabilize the ankle joint. As the person steps down, there is a small eccentric muscular activity in the soleus muscle as it contributes to the controlled drop and forward movement of the body. In the final phase of support, the controlled lowering phase, the body is lowered onto the step primarily through eccentric muscle activity at the knee joint. There is a minimum amount of hip extensor activity at the end of this phase.


Several terms are used in gait studies to describe the timing of the key events. This terminology is necessary to understand the actions of the lower extremity in walking and running. In locomotion studies, a walking or running cycle is generally defined as the period from the contact of one foot on the ground to the next contact of the same foot. A gait cycle is usually broken down into two phases, referred to as the stance or support phase and the swing phase. In the stance or support phase, the foot is in contact with the ground. The support phase can also be broken down into subphases. The first half of the support phase is the braking phase, which starts with a loading or heelstrike phase and ends at midsupport. The second half of the support phase is the propulsion phase, which starts at midstance and continues to terminal stance and then to preswing as the foot prepares to leave the ground. The swing or noncontact phase is the period when the foot is not in contact with the ground, and it can be further subdivided into the initial swing phase, the midswing and the terminal swing subphases. Essentially, this phase represents the recovery of the limb in preparation for the next contact with the ground. These events are illustrated in Figure 6-41 for running and in Figure 6-42 for walking.


There is considerable muscle activity in multiple muscles during running, and the joint motions typically occur over a greater range of motion than in walking. The exception is hyperextension, which is greater in walking because of the increased stance time. The muscular activity in running, however, is similar to that seen in walking. In running, there are 800 to 2000 foot contacts with the ground per mile, and two to three times the body weight is absorbed by the foot, leg, thigh, pelvis, and spine (22).


FIGURE 6-41 In running, there is high level of muscular activity in the hamstrings, gluteus minimus, gluteus maximus, quadriceps femoris group, and intrinsic muscles of the foot during the right support phase of the activity. During the swing phase, there is substantial activity in the iliopsoas and the tensor fascia latae.

At the hip joint, the gluteus maximus controls flexion of the trunk on the stance side and decelerates the swing leg. The stance-side gluteus maximus also eccentrically controls flexion of the hip with the hamstrings (87,95). The gluteus medius and the tensor fascia latae are active in the initial braking portion of the support phase to control the pelvis in the frontal plane to keep it from tilting to the opposite side (95). During the propulsive portion of the support phase in running, the hamstrings are very active as the thigh extends. The gluteus maximus also contributes to extension during late stance while also generating external rotation until toe-off.

At the knee joint, both the quadriceps femoris muscles and the hamstrings are active during various portions of the stance phase (107). At the instant of heel strike in running, a brief concentric contraction of the hamstrings flexes the knee to decrease the horizontal or braking force being absorbed at impact. This is followed by activation of the quadriceps femoris. Initially, the quadriceps femoris act eccentrically to slow the negative vertical of the body velocity. This action lasts until midsupport. The quadriceps femoris then act concentrically to produce positive vertical velocity of the body. The hamstrings are also active with the quadriceps femoris to generate extension at the hip (93). The period from heel strike to midsupport represents more than half of the energy costs in running.

In the propelling portion of support, the quadriceps femoris are eccentrically active as the heel lifts off and then become concentrically active up through toe-off. The hamstrings are also concentrically active at toe-off.

Plantarflexor activity also increases sharply after heel strike and dominates through the total stance period (95). In the braking portion of stance, the plantarflexor muscles work not at the ankle but to eccentrically halt the vertical descent of the body over the foot. This continues into the propelling portion of support, when the plantarflexors shift to a concentric contraction, adding to the driving force of the run (95).




FIGURE 6-42 Lower extremity muscles involved in walking showing the level of muscle activity (low, moderate, high) and the type of muscle action (concentric [CON] and eccentric [ECC]) with the associated purpose.

As soon as the foot leaves the ground to begin the swing phase, the limb is brought forward by the iliopsoas and rectus femoris, slowing the thigh in hyperextension and moving the thigh forward into flexion. The rectus femoris is the most important muscle for forward propulsion of the body because it accounts for the large range of motion in the lower extremity. It initiates the flexion movement so vigorously that the iliopsoas action also contributes to knee extension. The iliopsoas is active for more than 50% of the swing phase in running (95). In the early part of the swing phase, there is activity in the adductors, which, as in walking, are working with the abductors to control the pelvis.

At the end of the swing phase, a great amount of eccentric muscular activity takes place in the gluteus maximus and the hamstrings as they begin to decelerate the rapidly flexing thigh. As the speed of the run increases, the activity of the gluteus maximus increases as it assumes more of the responsibility for slowing the thigh in preparation for foot contact in descent. Also, in the later portion of the swing phase, the abductors become active again as they lower the thigh eccentrically to produce adduction.

During the initial portion of the swing phase, the quadriceps femoris is active eccentrically to slow rapid knee flexion. In the later part of the swing phase, the


hamstrings become active to both limit knee extension and hip flexion (95).

When running at faster speeds, the lower extremity muscles must generate considerable power. If muscles groups are weak, the running stride can be affected. For example, a weak gluteus maximus can slow down the leg transition between recovery and swing. Weak hamstrings can result in a failure to control hip flexion and knee extension in late recovery and weaken the hip extension force in the support phase (20).


During walking, the muscles around the pelvis and the hip joint contribute minimally to the actual propulsion in walking and are more involved with control of the pelvis (90). The muscular contribution of the lower extremity muscles active in walking are summarized in Figure 6-42.

At heel strike, moderate activity in the gluteus medius and minimus of the weight-bearing limb keeps the pelvis balanced against the weight of the trunk. The abduction muscle force balances the trunk and the swing leg about the supporting hip (93). This activity continues until mid-support and then drops off in late stance (143). The adductors also work concurrently with both of these muscles to control the limb during support. The gluteus maximus is active at heel strike to assist with the movement of the body over the leg. Finally, the tensor fascia latae are active from heel strike to midsupport to assist with frontal plane control of the pelvis (143).

The hamstrings reach their peak of muscular activity as they attempt to arrest movement at the hip joint at heel strike. The quadriceps femores then begin to contract to control the load (i.e., weight) being imposed on the knee joint by the body and the reaction force coming up from the ground. The knee also moves into flexion eccentrically controlled by the quadriceps femoris. A co-contraction of the hamstrings and the quadriceps femoris continues until the foot is flat on the ground, at which time the activity of the hamstrings drops off. The activity of the quadriceps femoris diminishes at approximately 30% of stance and is silent through midsupport and into the initial phases of propulsion.

In the propelling portion of the support phase of walking, the quadriceps femoris become active again around 85% to 90% of stance, when they are used to propel the body upward and forward. The hamstrings become active at approximately the same time to add to the forward propulsion.

At the ankle, there is maximum activity in the dorsi-flexor muscles during heelstrike to eccentrically control the lowering of the foot to the ground in plantarflexion. The most muscle activity is seen in the tibialis anterior, extensor digitorum longus, and extensor hallucis longus (148). The activity in this muscle group decreases but maintains activity throughout the total stance phase.

There is little activity in the gastrocnemius and soleus at heel strike. They begin to activate after foot flat and continue into the propulsive phase as they control the movement of the tibia over the foot and generate propelling forces. The intrinsic muscles of the foot are inactive in this portion of stance.

In the propelling portion of support, the dorsiflexor muscles are still active, generating a second peak in the stance phase right before toe-off. The gastrocnemius and soleus reach a peak of muscular activity just before toe-off. The intrinsic muscles of the foot are active in the propelling phase of stance as they work to make the foot rigid and stable and control depression of the arch. Activity in the gastrocnemius, soleus, and intrinsic muscles ceases at toe-off

At the beginning of the swing phase, the limb must be swung forward rapidly. This movement is initiated by a vigorous contraction of the iliopsoas, sartorius, and tensor fascia latae. The thigh adducts in the middle of the swing phase and internally rotates just after toe-off. The adductors are active at the beginning of the swing phase and continue into the stance phase. At the end of the swing phase, activity from the hamstrings and the gluteus maximus decelerates the limb (143).

In the swing phase, the hamstrings are active after toe-off and again at the end of the swing just before foot contact. Similar activity is seen in the quadriceps femoris, which slow knee flexion after toe-off and initiate knee extension prior to heel strike.

During the swing phase, the dorsiflexor muscles generate the only significant muscular activity in the ankle and foot. They hold the foot in a dorsiflexed position so that the foot clears the ground while the limb is swinging through.


In cycling, the key events are determined from the rotation of the crank of the bicycle. The motion of the crank forms a circle. A cycle is one revolution of this circle with 0° at the 12 o'clock position, 90° at 3 o'clock, 180° at 6 o'clock, and 270° at 9 o'clock. The end of the cycle occurs at 360° (or 0°), back at the 12 o'clock position. The 12 o'clock position is also referred to as top dead center, and the 6 o'clock position is referred to as bottom dead center. These events are presented in Figure 6-43.

The direction of the forces applied to the pedal changes during knee leg extension and coactivation of agonists and antagonists occurs throughout the cycle. The quadriceps femoris muscles are the primary force producers with assistance from the other lower extremity muscles. At the hip joint, the gluteus maximus becomes active in the downstroke after about 30° into the cycle and continues through approximately 150° to extend the hip. As the activity from the gluteus maximus begins to decline, the activity of the hamstrings increases in the second quadrant and continues from approximately 130° to 250° as they extend the hip and begin to flex the knee (48). At the top of the crank cycle, from 0 to 90°, the quadriceps femoris is very active. The rectus femoris is active through the arc of 200° to 130° of the next cycle. The vastus medialis is


active from 300 to 135°, and the vastus lateralis is active from 315° through 130° of the next cycle (132).


FIGURE 6-43 Lower extremity muscles involved in cycling showing the level of muscle activity (low, moderate, high) and the type of muscle action (concentric [CON] and eccentric [ECC]) with the associated purpose.

In the middle of the cycle, from 90° to 270°, the hamstrings contribute more to power production, with the biceps femoris active from 5° to 265° and the semimembranosus active from 10° to 265° (132). There is co-contraction of the quadriceps femoris and the hamstrings throughout the entire cycle but in different and changing proportions. In the last portion of the cycle, from 270° to 360°, the rectus femoris is actively involved as the leg is brought back up into the top position.

At the ankle, the gastrocnemius contributes through most of the power portion of the cycle, and is active from 30° to 270° in the revolution. When the activity of the gastrocnemius ceases, the tibialis anterior becomes active from 280° until slightly past top dead center, thus contributing to the lift of the pedal. Again, when the tibialis anterior activity ceases, the gastrocnemius becomes active. Unlike the knee and hip, the ankle does not co-contract.

Forces Acting on Joints in the Lower Extremity

The lower extremity joints can be subjected to high forces generated by muscles, body weight (BW), and ground reaction forces. The ground reaction forces generated in basic activities such as walking or stair climbing are 1.1 to 1.3 BW and 1.2 to 2.0 BW, respectively (153). Landing vertical forces are even higher (2.16 to 2.67 BW), and drop landings have been shown to generate maximum ground reaction forces in the range of 8.5 BW in children (10,76,150,171).

Hip Joint

Even Just Standing On Two Limbs Loads The Hip Joint With A Force Equivalent To 30% of Body Weight (152). This Force Is Generated Primarily By The Body Weight Above The Hip Joint and Is Shared By Right and Left Joints. When A Person Stands On One Limb, The Force Imposed On The Hip Joint Increases Significantly, To Approximately 2.5 To 3 Times Body Weight (143,152). This Is Mainly The Result of the Increase In The Amount of Body Weight Previously Shared With The Other Limb and A Vigorous Muscular Contraction of the Abductors. The Increased Muscular Force of the Abductors Generates High Hip Joint Forces As They Work To Counter The Effects of Gravity and Control The Pelvis.

In stair climbing, hip joint forces can reach levels of 3 times body weight and are on average 23% higher than walking (13); in walking, the forces range from 2.5 to 7


times body weight; and in running, the forces can be as high as 10 times body weight (68,80,119,143,152). In one study, hip joint forces (5.3 BW) were higher in running compared than in skiing on long turns and a flat slope (4.1 BW), but short turns and steep slope skiing generated the highest hip joint forces (7.8 BW) (162). Cross-country skiing loaded the hip joint with 4.6 BW, which was less than walking (162). Fortunately, the hip joint can withstand 12 to 15 times body weight before fracture or breakdown in the osseous component occurs (143).

Knee Joint

The knee is also subject to very high forces during most activities, whether generated in response to gravity, as a result of the absorption of the force coming up from the ground, or as a consequence of muscular contraction. The muscles generate considerable force, with the quadriceps femoris tension force being as high as 1 to 3 times body weight in walking, 4 times body weight in stair climbing, 3.4 times body weight in climbing, and 5 times body weight in a squat (26).

The tibiofemoral compression force can also be quite high in specific activities. For example, in a knee extension exercise, muscle forces applied against a low resistance (40 Nm [newton-meters]) can create tibiofemoral compression forces of 1100 N during knee extension acting through knee angles of 30° to 120°. This force increases to 1230 N when extension occurs from the fully extended position (116). Tibiofemoral compression force in the extended position is greater, partly because the quadriceps femoris group loses mechanical advantage at the terminal range of motion and thus has to exert a greater muscular force to compensate for the loss in leverage.

The tibiofemoral shear force is maximum in the last few degrees of knee extension. The direction of the shear force changes with the amount of flexion in the joint, changing direction between 50° and 90° of flexion. Operating against the same 40-Nm resistance in extension, there is posterior shear of 200 N at 120° of flexion and 600 N of anterior shear in extension (116). This is partially because when nearing extension, the patellar tendon pulls the tibia anteriorly relative to the femur, but in flexion, it pulls the tibia posteriorly. The anterior force in the last 30° of extension places a great deal of stress on the ACL, which takes up 86% of the anterior shear force. By moving the contact pad closer to the knee in an extension exercise, the shear force can be directed posteriorly, taking the strain off of the ACL (116).

Even though tibiofemoral compression forces are greater in the extended position, the contact area is large, which reduces the pressure. There is 50% more contact area at the extended position than in 90° of flexion. Thus, in the extended position, the compression forces are high, but the pressure is less by 25% (116). The forces for women are 20% higher because of a decreased mechanical advantage associated with a shorter moment arm. Because women also have less contact area in the joint, greater pressure is created, accounting for the higher rate of osteoarthritis in the knees of women, an occurrence not seen in the hip.

Tibiofemoral compression forces during isokinetic knee extension (180°/sec) has been found to be very high with a maximum of 6300 N or 9 times body weight (117). During cycling, the tibiofemoral compressive force has been recorded at 1.0 to 1.2 BW (47,114). Whereas tibiofemoral compression forces for walking are in the range of 2.8 to 3.1 body weight (4,108,158), the tibiofemoral shear forces are in the range of 0.6 body weight (158). In stair ascent, tibiofemoral compression and shear forces have been recorded as high as 5.4 and 1.3 body weight, respectively (158).

The patellofemoral compressive force approximates 0.5 to 1.5 times body weight in walking, 3 to 4 times body weight in climbing, and 7 to 8 times body weight in a squat exercise (116). The patellofemoral joint absorbs compressive forces from the femur and transforms them into tensile forces in the quadriceps and patellar tendon. In vigorous activities, in which there are large negative acceleration forces, the patellofemoral force is also large. This force increases with flexion because the angle between the quadriceps femoris and the patella decreases, requiring greater quadriceps femoris force to resist the flexion or produce an extension.

The patellofemoral compressive force is maximum at 50° of flexion and declines at extension, approaching zero as the patella almost comes off the femur. The largest area of contact with the patella is at 60° to 90° of knee flexion. Of the patellar surface, 13% to 38% bears the force in joint loading (116). Fortunately, there is a large contact area when the patellofemoral compressive forces are large, which reduces the pressure. In fact, there is considerable pressure in the extended position even though the patellofemoral force is low because the contact area is small.

Activities using more pronounced knee flexion angles usually involve large patellofemoral compressive forces. These include descending stairs (4000 N), maximal isometric extension (6100 N), kicking (6800 N), the parallel squat (14,900 N), isokinetic knee extension (8300 N), rising from a chair (3800 N), and jogging (5000 N) (67). In activities that use lesser amounts of knee flexion, the force is much less. Examples include ascending stairs (1400 N), walking (840 to 850 N), and bicycling (880 N) (116). The activities with high patellofemoral forces should be limited or avoided by individuals with patellofemoral pain.

The patellofemoral compressive force and the quadriceps femoris force both increase at the same rate with knee flexion in weight bearing. If the leg extends against a resistance, such as in a leg extension machine or weight boot, the quadriceps femoris force increases, but the patellofemoral force decreases from flexion to extension. Because the function in a weight-lifting extension exercise is opposite that in daily activities that use flexion in the


weight-bearing position, the use of a weight-bearing closed kinetic chain activity is preferable. At knee flexion angles greater than 60°, the patellar tendon force is only half to two thirds that of the quadriceps tendon force (116).

Those with pain in the patellar region should avoid exercising at angles greater than 30° to avoid large flexing moments and patellofemoral compression forces. However, in extension, when the patellofemoral force is low, the anterior shear force is high, making terminal extension activities contraindicated for any ACL injury (116). There is a reversal at 50° of flexion, when the shear force is low and the patellofemoral compression force is high.

Ankle and Foot

The ankle and foot are subjected to significant compressive and shear forces in both walking and running. In walking, a vertical force 0.8 to 1.1 times body weight comes at heel strike. The magnitude of this force decreases to about 0.8 times body weight in the midstance to 1.3 times body weight at toe-off (33,140). This force, along with the contraction force of the plantar flexors, creates a compression force in the ankle.

In walking, the compression force in the ankle joint can be as high as 3 times body weight at heel strike and 5 times body weight at toe-off A shear force of 0.45 to 0.8 times body weight is also present, primarily as a result of the shear forces absorbed from the ground and the position of the foot relative to the body (27,33,56). In running, the peak ankle joint forces are predicted to range from 9 to 13.3 times body weight. The peak Achilles tendon force can be in the range of 5.3 to 10 times body weight (27). The ankle joint is subjected to forces similar to those in the hip and knee joints. Amazingly, the ankle joint has very little incidence of osteoarthritis. This may be partly attributable to the large weight-bearing surface in the ankle, which lowers the pressure on the joint.


FIGURE 6-44 A. Forces applied to the plantar surface of the foot during gait normally travel a path from the lateral heel to the cuboid and across to the first and second metatarsal. B. High loading and extreme foot positions have been associated with a variety of injuries.

The subtalar joint is subjected to forces equivalent to 2.4 times body weight, with the anterior articulation between the talus, calcaneus, and navicular recording forces as high as 2.8 times body weight (33,140). Large loads on the talus must be expected because it is the keystone of the foot. Loads travel into the foot from the talus to the calcaneus and then forward to the navicular and cuneiforms.

During locomotion, forces applied to the foot from the ground are usually applied to the lateral aspect of the heel, travel laterally to the cuboid, and then transfer to the second metatarsal and the hallux at toe-off. In Figure 6-44, the path of the forces across the plantar surface of the foot is shown. The greatest percentage of support time is spent in contact with the forefoot and the first and second metatarsal. If the contact time of the second metatarsal is longer than that of the first metatarsal, a condition known as Morton's toe develops, and the pressure on the head of the second metatarsal is greatly increased (140). This pattern of foot strike and transfer of the forces across the foot depends on a variety of factors and can vary with speed, foot type, and the foot contact patterns of individuals.

Forces in running are two times greater than those seen in walking. At foot strike, the forces received from the


ground create a vertical force of 2.2 times body weight and 0.5 times body weight shear force. A vertical force of 2.8 times body weight and a shear force of 0.5 times body weight are produced at toe-off (33,140). With the addition of the muscular forces, the compressive forces can be as high as 8 to 13 times body weight in running. The anterior shear forces can be in the range of 3.3 to 5.5 times body weight, the medial shear force in the range of 0.8 times body weight, and lateral shear force in the range of 0.5 times body weight (33). Forces are large because the foot must transmit them between the body and the foot as well as the ground and the body. Given the injury record for the ankle and the foot, the foot is resilient and adaptable to the forces it must control with each step in walking or running.


The lower extremity absorbs very high forces and supports the body's weight. The lower limbs are connected by the pelvic girdle, making every movement or posture of the lower extremity or trunk interrelated.

The pelvic girdle serves as a base for lower extremity movement and a site for muscular contraction, and it is important in the maintenance of balance and posture. The pelvic girdle consists of three coxal bones (ilium, ischium, pubis) that are joined in the front at the pubic symphysis and connected to the sacrum in the back (sacroiliac joint). The pelvic and sacral movements of flexion, extension, posterior and anterior tilt, and rotation accompany movements of the thigh and the trunk.

The femur articulates at the acetabulum on the anterolateral surface of the pelvis. This ball-and-socket joint is well reinforced by strong ligaments that restrict all movements of the thigh except for flexion. The femoral neck is angled at approximately 125° in the frontal plane, and an increase (coxa valga) or decrease (coxa vara) in this angle influences leg length and lower extremity alignment and function. The angle of anteversion in the transverse plane also influences the rotation characteristics of the lower extremity.

The hip joint allows considerable movement in flexion (120° to 125°) produced by the hip flexors, iliopsoas, rectus femoris, sartorius, pectineus, and tensor fascia latae. The range of hyperextension is 10° to 15°. Hip extension is produced by the hamstrings, semimembranosus, semitendinosus, biceps femoris, and gluteus max-imus. Abduction range of motion is 30° and is produced by the gluteus medius, gluteus minimus, tensor fascia latae, and piriformis. Adduction (30°) is produced by the gracilis, adductor longus, adductor magnus, adductor brevis, and pectineus. Internal rotation through approximately 50° is produced by the gluteus minimus, gluteus medius, gracilis, adductor longus, adductor magnus, tensor fascia latae, semimembranosus, and semitendinosus. External rotation through 50° is produced by the gluteus maximums, obturator externus, quadratus femoris, obturator internus, piriformis, and inferior and superior gemellus.

Movements of the thigh are usually accompanied by a pelvic movement and vice versa. For example, hip flexion in an open chain is accompanied by a posterior tilt of the pelvis. This reverses in a closed-chain weight-bearing position in which hip flexion is accompanied by an anterior movement of the pelvis on the femur.

The hip muscles can produce greater strength in the extension because of the large muscle mass from the hamstrings and the gluteus maximus. Extension strength is maximized from a hip flexion position. Strength output in the other movements can also be maximized with accompanying knee flexion for hip flexion strength facilitation, accompanying thigh flexion for the abduction movement, slight abduction for adduction facilitation, and hip flexion for the internal rotators.

Conditioning exercises for the lower extremity are relatively easy to implement because they include common movements associated with daily living activities. A closed kinetic chain exercise is beneficial for the lower extremity because of the transfer to daily activities. Because of the many two-joint muscles surrounding the hip joint, the position of adjacent joints is important. The hip flexors are best exercised with the person supine or hanging. The extensors are maximally stretched using a hip flexion position with the knees extended. The abductors, adductors, and rotators require creative approaches to conditioning because they are not easy to isolate.

The hip joint is durable and accounts for only a very small percentage of injuries to the lower extremity. Common soft tissue injuries to the region include tendinitis of the gluteus medius; strain to the rectus femoris, hamstrings, iliopsoas, or piriformis; bursitis; and iliotibial band friction syndrome. Stress fractures are also more prevalent at sites such as the anterior iliac spine, pubic rami, ischial tuberosity, greater and lesser trochanters, and femoral neck. Common childhood disorders to the hip joint include congenital hip dislocation and Legg-Calvé-Perthes disease. The hip joint is also a site where osteoarthritis is prevalent in later years.

The knee joint is very complex and is formed by the articulation between the tibia and the femur (tibiofemoral joint) and the patella and the femur (patellofemoral joint). In the tibiofemoral joint, the two condyles of the femur rest on the tibial plateau and rely on the collateral ligaments, cruciate ligaments, menisci, and joint capsule for support. The patellofemoral joint is supported by the quadriceps tendon and the patellar ligament. The patella fits into the trochlear groove of the femur, which also offers stabilization to the patella.

An important alignment feature at the knee joint is the Q-angle, the angle representing the position of the patella with respect to the femur. An increase in this angle increases the valgus stress on the knee joint. High Q-angles are most common in females because of their wider pelvic girdles.



Flexion at the knee joint occurs through approximately 120° to 145° and is produced by the hamstrings, biceps femoris, semimembranosus, and semitendinosus. Accompanying flexion is internal rotation of the tibia, which is produced by the sartorius, popliteus, gracilis, semimembranosus, and semitendinosus. As the knee joint flexes and internally rotates, the patella also moves down in the groove and then moves laterally.

Extension at the knee joint is produced by the powerful quadriceps femoris muscle group, which includes the vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius. When the knee extends, the tibia externally rotates via action by the biceps femoris. At the end of extension, the knee joint locks into the terminal position by a screw-home movement in which the condyles rotate into their final positions. In extension, the patella moves up in the groove and terminates in a resting position that is high and lateral on the femur.

The strength of the muscles around the knee joint is substantial, with the extensors being one of the strongest muscle groups in the body. The extensors are stronger than the flexors in all joint positions but not necessarily at all joint speeds. The flexors should not be significantly weaker than the extensors, or the injury potential around the joint will increase.

Conditioning of the knee extensors is an easy task because these muscles control simple lowering and rising movements. Closed-chain exercises are also very beneficial for the extensors because of their relation to daily living activities. The flexors are also exercised during a squat movement because of their action at the hip joint but can best be isolated and exercised in a seated position.

The knee is the most frequently injured joint in the body. Traumatic injuries damage the ligaments or menisci, and numerous chronic injuries result in tendinitis, iliotib-ial band syndrome, and general knee pain. Muscle strains to the quadriceps femoris and hamstrings are also common. The patella is a site for injuries such as subluxation and dislocation and other patellar pain syndromes, such as chondromalacia patella.

The foot and ankle consist of 26 bones articulating at 30 synovial joints, supported by more than 100 ligaments and 30 muscles. The ankle, or talocrural joint, has two main articulations, the tibiotalar and tibiofibular joints. The tibia and fibula form a mortise over the talus defined on the medial and lateral sides by the malleoli. Both sides of the joint are strongly reinforced by ligaments, making the ankle very stable.

The foot moves at the tibiotalar joint in two directions, plantarflexion and dorsiflexion. Plantarflexion can occur through a range of motion of approximately 50° and is produced by the gastrocnemius and soleus with some assistance from the peroneal muscles and the toe flexors. Dorsiflexion range of motion is approximately 20°, and the movement is created by the tibialis anterior and the toe extensors.

Another important joint in the foot is the subtalar or talocalcaneal joint, in which pronation and supination occur. At this joint, the rotation of the lower extremity and forces of impact are absorbed. Pronation at the subtalar articulation is a triplane movement that consists of calcaneal eversion, abduction, and dorsiflexion with the foot off the ground and calcaneal eversion, talar adduction, and plantarflexion with the foot on the ground in a closed chain. Muscles responsible for creating eversion are the peroneals, consisting of the peroneus longus, peroneus brevis, and per-oneus tertius. Supination, the reverse movement, is created in the open chain through calcaneal inversion, talar adduction, and plantarflexion and in the closed chain through calcaneal inversion, talar abduction, and dorsiflexion. Muscles responsible for producing inversion are the tibialis anterior, tibialis posterior, and hallux flexors and extensors. The range of motion for pronation and supination is 20° to 62°.

The midtarsal joint also contributes to pronation and supination of the foot. These two joints, the calcaneocuboid and the talonavicular, allow the foot great mobility if the axes of the two joints lie parallel to each other. This is beneficial in the early portion of support, when the body is absorbing forces of contact. When these axes are not parallel, the foot becomes rigid. This is beneficial in the later portion of support, when the foot is propelling the body up and forward. Numerous other articulations in the foot, such as the intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal joints, influence both total foot and toe motion.

The foot has two longitudinal arches that provide both shock absorption and support. The medial arch is higher and more dynamic than the lateral arch. The longitudinal arches are supported by the plantar fascia running along the plantar surface of the foot. Transverse arches running across the foot depress and spread in weight bearing. The shape of the arches and the bony arrangement determine foot type, which can be normal, flat, or high arched and flexible or rigid. An extremely flat foot is termed pes planus, and a high-arched foot is called pes cavus. Other foot alignments include forefoot and rear foot varus and valgus, a plantarflexed first ray, and equinus positions that influence function of the foot.

Plantarflexion of the foot is a very strong joint action and is a major contributor to the development of a propulsion force. Dorsiflexion is weak and not capable of generating high muscle forces.

The muscles of the foot and ankle receive a considerable amount of conditioning in daily living activities such as walking. Specific muscles can be isolated through exercises. For example, the gastrocnemius can be strengthened in a standing heel raise and the soleus in a seated heel raise. The intrinsic muscles of the foot can be exercised by drawing the alphabet or drawing figure-eights with the foot or by just going barefoot.

The foot and ankle are frequently injured in sports and physical activity. Common injuries are ankle sprains; Achilles tendinitis; posterior, lateral, or medial tibial syndrome; plantar fasciitis; bursitis; metatarsalgia; and stress fractures.



The muscles of the lower extremity are major contributors to a variety of movements and sport activities. In walking, the hip abductors control the pelvis, the hamstrings control the amount of hip flexion and provide some of the propulsive force, and the hip flexors are active in the swing phase. In running, the hip joint motions and the muscular activity increase, but the same muscles used in walking are also used. At the knee joint, the quadriceps femoris serves as a shock absorption mechanism and a power producer for walking, running, and stair climbing. In cycling, the quadriceps femoris is responsible for a significant amount of power production. Ankle joint muscles such as the gastrocnemius and soleus are also important contributors to walking, running, stair climbing, and cycling.

The lower extremity must handle high loads imposed by muscles, gravity and forces coming up from the ground. Loads absorbed by the hip joint can range from 2 to 10 times body weight in activities such as walking, running, and stair climbing.

The knee joint can handle high loads and commonly absorbs 1 to 5 times body weight in activities such as walking, running, and weight lifting. A maximum flexion position should be evaluated for safety, given the high shear forces that are present in the position. Patellofemoral forces can also be high, in the range of 0.5 to 8 times body weight, in daily living activities. The patellofemoral force is high in positions of maximum knee flexion. The foot and ankle can handle high loads, and the forces in the ankle joint range from 0.5 to 13 times body weight in walking and running. The subtalar joint also handles forces in the magnitude of 2 to 3 times body weight.

Review Questions

True or False

  1. ____The meniscus is an important component of every joint in the body.
  2. ____The ACL is taut in knee extension
  3. ____Knee flexors are best exercised in a standing position
  4. ____The vastus medialis is only active in the last 20° of knee extension
  5. ____The female pelvis is wider than the male pelvis
  6. ____The lesser trochanter is vulnerable to avulsion fractures from the force of the iliopsoas muscle
  7. ____The talus has multiple muscles that attach to it.
  8. ____Forefoot varus occurs when the medial side of the forefoot lifts
  9. ____Plantarflexion strength is greatest with the knees flexed and the foot in a position of slight dorsiflexion
  10. ____The patellofemoral force is higher going up stairs than in coming down stairs.
  11. ____Calcaneal eversion is present in both closed- and open-chain pronation
  12. ____In a weight-bearing position, anterior tilt of the pelvis accompanies hip hyperextension

13.____ Coxa valga can increase the load on the femora head

  1. ____The angle of inclination of the femur is larger at birth and in older adults
  2. ____The hip muscles can generate the greatest strength in extension
  3. ____The pes anserinus is an important ligament inside the hip joint.
  4. ____In a cycling movement, the quadriceps and the hamstrings contract together in varying degrees throughout the whole cycle
  5. ____The load on the hip joint in a single-leg stance is twice that of standing on two legs
  6. ____Internal rotation accompanies flexion at the knee joint.
  7. ____Hip hyperextension is always greater in running than walking
  8. ____The lateral side of the ankle is more susceptible to sprains
  9. ____Hip flexors are best exercised in a hanging position
  10. ____Bowleggedness is also termed genu valgum
  11. ____The hamstring to quadriceps strength ratio is 0.5 across all testing speeds
  12. ____The hip joint has good ligamentous support in all movement directions

Multiple Choice

  1. Most of the injuries to the hip joint occur to the soft tissue as a result of:
  2. running
  3. leg length discrepancy
  4. varum alignment in the lower extremity
  5. All of the above
  6. Pronation is typically higher in individuals with:
  7. high arches
  8. tibial or rearfoot varum
  9. a small Q-angle
  10. rearfoot valgus
  11. The primary internal rotator(s) at the knee is (are):
  12. semimembranosus
  13. semitendinosus
  14. biceps femoris
  15. all of the above
  16. Both A and B
  17. The sacroiliac joint
  18. transmits the weight of the body to the hip
  19. is immobile in males
  20. has stronger and thicker ligaments in males
  21. moves in extension when the as the base moves anteriorly with trunk extension
  22. The sacral movements are
  23. flexion, extension, and rotation
  24. flexion, extension, nutation, and counternutation



  1. flexion, extension, abduction, adduction, and rotation
  2. flexion and extension
  3. Higher quadriceps activity in an open-chain leg extension activity:
  4. is higher with more knee flexion
  5. is higher with more knee extension
  6. is higher in the supine position
  7. is higher with the trunk flexed
  8. The average range of motion for plantarflexion is
  9. 20°
  10. 35°
  11. 50°
  12. 70°
  13. Medial tibial syndrome is usually associated with irritation of:
  14. the insertion of the tibialis posterior
  15. the periosteum
  16. the insertion of the tibialis anterior
  17. All of the above
  18. Both A and B
  19. The muscles that attach into the iliotibial band include the
  20. sartorius
  21. tensor fascia latae
  22. gluteus medius
  23. All of the above
  24. Both A and B
  25. The lateral meniscus
  26. is larger than the medial meniscus
  27. is crescent shaped
  28. connects to the LCL
  29. is wedge shaped
  30. The pubofemoral ligament resists the movements of:
  31. adduction
  32. internal rotation
  33. flexion
  34. abduction
  35. All of the above
  36. Both A and B
  37. Support on the medial side of the knee joint comes from the:
  38. tibial collateral
  39. joint capsule
  40. semimembranosus
  41. All of the above
  42. Both A and B
  43. During the support phase of running,
  44. pronation accompanies internal rotation of the knee
  45. pronation accompanies flexion of the knee
  46. supination accompanies internal rotation of the knee
  47. supination accompanies flexion of the knee
  48. Both A and B
  49. Both A and D
  50. When the Achilles tendon is short,
  51. the heel raises later in the support phase
  52. heel walking is more common
  53. an equinus foot deformity is present
  54. the soleus is more active in the support phase
  55. The pelvis moves
  56. anteriorly with closed-chain hip extension
  57. posteriorly with open-chain hip extension
  58. posteriorly with open-chain hip flexion
  59. anteriorly with closed-chain hip flexion
  60. All of the above
  61. Both A and B
  62. Both C and D
  63. The normal range of motion at the knee joint is:
  64. 5° to 10° of hyperextension
  65. 90° of external rotation
  66. 130° to 145° of flexion
  67. All of the above
  68. Both A and B
  69. During knee flexion, the patella moves
  70. up, laterally, and rotates medially
  71. down, laterally, and rotates externally
  72. up, adducts, and rotates externally
  73. down, adducts and rotates medially
  74. Slipped capital femoral epiphysitis
  75. occurs more often in young girls ages 2 to 4 years
  76. produces a pain in the back of the hip joint
  77. causes an externally rotated gait
  78. is caused by a calcium nutritional deficiency
  79. The soleus
  80. can cause a functional short leg
  81. is active in standing
  82. is best exercised in a seated position
  83. All of the above
  84. Both A and B
  85. The patellofemoral compression force can be as high as ___body weights in a squat exercise
  86. 10
  87. 8
  88. 6
  89. 4
  90. The____are the major power producers in cycling
  91. plantarflexors
  92. quadriceps
  93. hamstrings
  94. gluteal muscles
  95. The knee can flex through a greater range of motion when the
  96. thigh is hyperextended
  97. foot is pronating
  98. thigh is flexed
  99. foot is supinating
  100. All of the above
  101. Both A and B
  102. The knee joint is considered to be a
  103. modified hinge joint
  104. condyloid joint
  105. double condyloid joint
  106. all of the above
  107. The adductor muscles
  108. are important in activities such as soccer and dance
  109. work with the same side abductors to balance the pelvis in the frontal plane during gait
  110. aid in producing lateral rotation of the hip
  111. All of the above
  112. Both A and B



  1. Plantar fascitis is
  2. more predominant in high-arched individuals
  3. more irritated in descending stairs
  4. is usually painful on the underside of the calcaneus
  5. All of the above
  6. Both A and B


  1. Adelaar, R (1986). The practical biomechanics of running. American Journal of Sports Medicine, 14:497-500.
  2. Adkins, S. B., Figler, R A. (2001). Hip pain in athletes. American Family Physician, 61:2109-2118.
  3. Amendola, A., Wolcott, M. (2002). Bony injuries around the hip. Sports Medicine and Arthroscopy Review, 10:163-167.
  4. Anderson, F. C, Pandy, M. G. (2001). Static and dynamic optimization solutions for gait are practically equivalent. Journal of Biomechanics, 34:53-161.
  5. Anderson, K, et al. (2001). Hip and groin injuries in athletes. The American Journal of Sports Medicine, 29:521-533.
  6. Andersson, E.A., et al. (1997). Abdominal and hip flexor muscle activation during various training exercises. European Journal of Applied Physiology, 75:115-123.
  7. Apkarian, J., et al. (1989). Three-dimensional kinematic and dynamic model of the lower limb. Journal of Biomechanics, 22:143-155.
  8. Areblad, M., et al. (1990). Three-dimensional measurement of rear foot motion during running. Journal of Biomechanics, 23:933-940.
  9. Bates, B. (1983). Foot function in running: Researcher to coach. In J. Terauds (Ed.). Biomechanics in Sports.Del Mar, CA: Academic Publishers, 293-303.
  10. Bauer, J. J., et al. (2001). Quantifying force magnitude and loading rate from drop landings that induce osteogenesis. Journal of Applied Biomechanics, 17:142-152.
  11. Baum, B. S., Li, L. (2003). Lower extremity muscle activities during cycling are influenced by load and frequency. Journal of Electromyography and Kinesiology, 13:181-190.
  12. Bazzoli, A., Pollina, F. (1989). Heel pain in recreational runners. Physician and Sportsmedicine, 17:55-56.
  13. Bergmann, G., et al. (2001). Hip contact forces and gait patterns from routine activities. Journal of Biomechanics, 34:859-871.
  14. Besier, T F., et al. (2005). Patellofemoral joint contact area increases with knee flexion and weight bearing. Journal of Orthopaedic Research, 23:345-350.
  15. Beutler, A. I., et al. (2002). Electromyographic analysis of single leg closed chain exercises: implications for rehabilitation after anterior cruciate ligament reconstruction.Journal of Athletic Training, 37:13-18.
  16. Beynnon B. D., et al. (1997). The strain behavior of the anterior cruciate Ligament during squatting and active extension: A comparison of an open- and a closed-kinetic chain exercise. The American Journal of Sports Medicine, 25: 823-829.
  17. Beynnon, B. D., et al. (2001). Ankle ligament injury risk factors: A prospective study of college athletes. Journal of Orthopaedic Research, 19:213-220.
  18. Blackburn, T A., Craig, E. (1980). Knee anatomy: A brief review. Physical Therapy, 60:1556-1560.
  19. Blackburn, T A., et al. (1982). An introduction to the plica. Journal of Orthopaedic and Sports Physical Therapy, 3:171-177.
  20. Blazevich, A. J. (2000). Optimizing hip musculature for greater sprint running speed. NSCA Strength and Conditioning Journal, 22:22-27.
  21. Boyd, K T, et al. (1997). Common hip injuries in sport. Sports Medicine, 24:273-288.
  22. Brody, D. M. (1980). Running injuries. Clinical Symposium, 32:2-36.
  23. Brown, D. A. (1996). Muscle activity patterns altered during pedaling at different body orientations. Journal of Biomechanics, 10:1349-1356.
  24. Brown, L. P., Yavarsky, P. (1987). Locomotor biomechanics and pathomechanics: A review. Journal of Orthopaedic and Sports Physical Therapy, 9:3-10.
  25. Browning, K H. (2001). Hip and pelvis injuries in runners: Careful examination and tailored management. The Physician and Sports Medicine, 29:23-34.
  26. Buchbinder, M. R, et al. (1979). The relationship of abnormal pronation to chondromalacia of the patella in distance runners. Podiatric Sports Medicine, 69:159-162.
  27. Burdett, R G. (1982). Forces predicted at the ankle during running. Medicine and Science in Sports and Exercise, 14:308-316.
  28. Bynum, E. B., et al. (1996). Open versus closed chain kinetic exercises after anterior cruciate ligament reconstruction. A prospective randomized study. The American Journal of Sports Medicine, 23:401-406.
  29. Cerny, K, et al. (1990). Effect of an unrestricted knee-ankle-foot orthosis on the stance phase gait in healthy persons. Orthopedics, 13:1121-1127.
  30. Chesworth, B. M., et al. (1989). Validation of outcome measures in patients with patellofemoral syndrome. Journal of Sports Physical Therapy, 10(8):302-308.
  31. Clark, T E., et al. (1983). The effects of shoe design parameters on rearfoot control in running. Medicine and Science in Sports and Exercise, 5:376-381.
  32. Colby, S. (2000). Electromyographic and kinematic analysis of cutting maneuvers. The American Journal of Sports Medicine, 28:234-240.
  33. Czerniecki, J. M. (1988). Foot and ankle biomechanics in walking and running. American Journal of Physical Medicine and Rehabilitation, 67:246-252.
  34. Davies, G. J., et al. (1980). Knee examination. Physical Therapy, 60:1565-1574.
  35. Davies, G. J., et al. (1980). Mechanism of selected knee injuries. Physical Therapy, 60:1590-1595.
  36. Dewberry, M. J., et al. (2003). Pelvic and femoral contributions to bilateral hip flexion by subjects suspended from a bar. Clinical Biomechanics, 18:494–499.
  37. DeVita, P., Stribling, J. (1991). Lower extremity joint kinetics and energetics during backward running. Medicine and Science in Sports and Exercise, 23:602-610.
  38. DiStefano, V. (1981). Anatomy and biomechanics of the ankle and foot. Athletic Training, 16:43-47.
  39. Donatelli, R (1987). Abnormal biomechanics of the foot and ankle. Journal of Orthopaedic and Sports Physical Therapy, 9:11-15.
  40. DonTigny, R L. (1985). Function and pathomechanics of the sacroiliac joint: A review. Physical Therapy, 65:35–43.



  1. Draganich, L. F., et al. (1989). Coactivation of the hamstrings and quadriceps during extension of the knee. The Journal of Bone and Joint Surgery, 71:1075-1081.
  2. Drez, D. Jr., et al. (1982). Nonoperative treatment of double lateral ligament tears of the ankle. American Journal of Sports Medicine, 10:197-200.
  3. Drysdale, C. L., et al. (2004). Surface electromyographic activity of the abdominal muscles during pelvic-tilt and abdominal-hollowing exercises. Athletic training, 39:32-36.
  4. Earl, J. E. (2005). Gluteus medius activity during 3 variations of isometric single-leg stance. Journal of Sport Rehabilitation, 14:1-11.
  5. Earl, J. E., et al. (2001). Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction. Journal of Electromyography and Kinesiology, 11:381-386.
  6. Engsberg, J. R, Andrews, J. G. (1987). Kinematic analysis of the talocalcaneal/talocrural joint during running support. Medicine and Science in Sports and Exercise, 19:275-284.
  7. Ericson, M. O., Nisell, R (1986). Tibiofemoral joint forces during ergometer cycling. The American Journal of Sports Medicine, 14:285-290.
  8. Erickson, M. O., et al. (1986). Power output and work in different muscle groups during ergometer cycling. European Journal of Applied Physiology, 55:229-235.
  9. Escamilla, R F., et al. (1998). Biomechanics of the knee during closed kinetic and open kinetic chain exercises. Medicine and Science in Sports and Exercise, 30:556-569.
  10. Fiore, R D., Leard, J. S. (1980). A functional approach in the rehabilitation of the ankle and rearfoot. Athletic Training, 15:231-235.
  11. Fleming, B. C., et al.(2005). Open- or closed-kinetic chain exercises after anterior cruciate ligament reconstruction? 33:134-140.
  12. Freedman, W., et al. (1976). EMG patterns and forces developed during step-down. American Journal of Physical Medicine, 55:275-290.
  13. Fukubayashi, T., Kurosawa, H. (1980). The contact area and pressure distribution pattern of the knee: A study of normal and osteoarthritic knee joints. Acta Orthopaedica Scandinavica, 51:871-879.
  14. Garrison, J. G., et al. (2005). Lower extremity EMG in male and female college soccer players during single-leg landing. Journal of sport rehabilitation, 14:48-57.
  15. Gehlsen, G. M ., et al. (1989). Knee kinematics: The effects of running on cambers. Medicine and Science in Sports and Exercise, 21:463-466.
  16. Giddings, V. L., et al.(2000). Calcaneal loading during walking and running. Medicine and Science in Sports and Exercise, 32, 627-634.
  17. Godges, J. J., et al. (1989). The effects of two stretching procedures on hip range of motion and gait economy. Journal of Orthopaedic and Sports Physical Therapy, 10(9):350-357.
  18. Grana, W. A., Coniglione, T C. (1985). Knee disorders in runners. Physician and Sportsmedicine, 13:127-133.
  19. Grelsamer, R P., et al. (2005). Men and women have similar Q angles: A clinical and trigonometric evaluation. Journal of Bone and Joint Surgery. British Volume, 87:1498-1501.
  20. Grieve, G. P. (1976). The sacroiliac joint. Journal of Anatomy, 58:384-399.
  21. Hamilton, J. J., Ziemer, L. K (1981). Functional anatomy of the human ankle and foot. In R H. Kiene, K A. Johnson (Eds.). Proceedings of the AAOS Symposium on the Foot and Ankle.St. Louis: Mosby, 1-14.
  22. Halbach, J. (1981). Pronated foot disorders. Athletic Training, 16:53-55.
  23. Heller, M. O., et al. (2001). Musculoskeletal loading conditions at the hip during walking and stair climbing. Journal of Biomechanics, 34:863-893.
  24. Hintermann, B. (1999). Biomechanics of the unstable ankle joint and clinical implications. Medicine and Science in Sports and Exercise, 31(suppl):459–469.
  25. Hodge, W. A., et al. (1987). The influence of hip arthroplasty on stair climbing and rising from a chair. In J. L. Stein (Ed.). Biomechanics of Normal and Prosthetic Gait.New York: American Society of Mechanical Engineers, 65-67.
  26. Hole, J. W. (1990). Human Anatomy and Physiology(5th Ed.). Dubuque, IA: William C. Brown.
  27. Hunt, G. C. (1985). Examination of lower extremity dysfunction. In J. Gould, G. J. Davies (Eds.). Orthopaedic and Sports Physical Therapy.St. Louis: Mosby, 408–436.
  28. Hurwitz, D.E., et al. (2003). A new parametric approach for modeling hip forces during gait. Journal of Biomechanics, 36:113-119.
  29. Hutson, M. A., Jackson, J. P. (1982). Injuries to the lateral ligament of the ankle: Assessment and treatment. British Journal of Sports Medicine, 4:245-249.
  30. Inman, V. T (1959). The influence of the foot-ankle complex on the proximal skeletal structures. Artificial Limbs, 13:59-65.
  31. Jacobs. C., et al. (2005). Strength and fatigability of the dominant and nondominant hip abductors. Journal of Athletic Training, 40:203-206.
  32. James, S. L., et al. (1978). Injuries to runners. American Journal of Sports Medicine, 6:40-50.
  33. Johnson, M. E., et al. (2004). Age-related changes in hip abductor and adductor joint torques. Archives of Physical Medicine and Rehabilitation, 85:593-597.
  34. Jorge, M., Hull, M. L. (1986). Analysis of EMG measurements during bicycle pedalling. Journal of Biomechanics, 19:683-694.
  35. Kapandji, I. A. (1970). The Physiology of'the Joints(Vol. 2). Edinburgh: Churchill Livingstone.
  36. Kernozek, T W., et al. (2005). Gender differences in frontal and sagittal plane biomechanics during drop landings. Medicine and Science in Sports and Exercise, 37:1003-1012.
  37. Kempson, G. E., et al. (1971). Patterns of cartilage stiffness on the normal and degenerative human femoral head. Journal of Biomechanics, 4:597-609.
  38. Kettlecamp, D. H., et al. (1970). An electrogoniometric study of knee motion in normal gait. Journal of Bone and Joint Surgery, 52(suppl A):775-790.
  39. Kosmahl, E., Kosmahl, H. (1987). Painful plantar heel, plantar fascitis, and calcaneal spur: Etiology and treatment. Journal of Orthopaedic and Sports Physical Therapy, 9:17-24.
  40. Krebs, D.E., et al. (1998) Hip biomechanics during gait. Journal of Sports Physical Therapy, 28:51-59.
  41. Kvist, J., Gillquist, J. (2001). Sagittal plane knee translation and electromyographic activity during closed and open kinetic chain exercises in anterior cruciate ligament-deficient patients and control subjects. The American Journal of Sports Medicine, 29:72-82.



  1. Lafortune, M. A., Cavanagh, P. R (1985). Three-dimensional kinematics of the patella during walking. In B. Jonsson (Ed.). Biomechanics X-A.Champaign, IL: Human Kinetics, 337-341.
  2. Lafortune, M. A., et al. (1992). Three-dimensional kinematics of the human knee during walking. Journal of Biomechanics, 25:347-357.
  3. Larson, R L. (1973). Epiphyseal injuries in the adolescent athlete. Orthopedic Clinics of North America, 4:839-851.
  4. Laubenthal, K. N., et al. (1972). A quantitative analysis of knee motion during activities of daily living. Physical Therapy, 52:34–42.
  5. Leib, F. J., Perry, J. (1971). Quadriceps function: An electromyographic study under isometric conditions. Journal of Bone and Joint Surgery, 53(suppl A):749-758.
  6. Lieberman, D. E., et al. (2006). The human gluteus maximus and its role in running. Journal of Experimental Biology, 209:2143-55.
  7. Lloyd-Smith, R, et al. (1985). A survey of overuse and traumatic hip and pelvic injuries in athletes. Physician and Sports Medicine, 13(10):131-141.
  8. Locke, M., et al. (1984). Ankle and subtalar motion during gait in arthritic patients. Physical Therapy, 64:504-509.
  9. Lovejoy, C. O. (1988). Evolution of human walking. Scientific American, 259(5):118-125.
  10. Lutz, G. E., et al. (1993). Comparison of tibiofemoral joint forces during open-kinetic-chain and closed-kinetic-chain exercises. Journal of Bone and Joint Surgery, 75:732-739.
  11. Lyon, K. K, et al. (1988). Q-angle: A factor in peak torque occurrence in isokinetic knee extension. Journal of Orthopaedic and Sports Physical Therapy, 9:250-253.
  12. MacKinnon, C. D., Winter, D. A. (1993). Control of whole body balance in the frontal plane during human walking. Journal of Biomechanics, 26:633-644.
  13. Majewski, M., Klaus, S. H. (2006). Epidemiology of athletic knee injuries: A 10 year study. Knee, 13:184-188.
  14. Mann, R A., et al. (1986). Comparative electromyography of the lower extremity in jogging, running, and sprinting. American Journal of Sports Medicine, 14:501-510.
  15. Markhede, G., Stener, G. (1981). Function after removal of various hip and thigh muscles for extirpation of tumors. Acta Orthopaedica Scandinavica, 52:373-395.
  16. Markhede, G., Grimby, G. (1980). Measurement of strength of the hip joint muscles. Scandinavian Journal of Rehabilitative Medicine, 12:169-174.
  17. Matheson G. O, et al. (1987). Stress fractures in athletes. A case study of 320 cases. American Journal of Sports Medicine, 15:46-58.
  18. McFadyen, B. J., Winter, D. A. (1988). An integrated biomechanical analysis of normal stair ascent and descent. Journal of Biomechanics, 21:733-744.
  19. McClusky, G. Blackburn, T A. (1980). Classification of knee ligament instabilities. Physical Therapy, 60:1575-1577.
  20. McLeod, W D., Hunter, S. (1980). Biomechanical analysis of the knee: Primary functions as elucidated by anatomy. Physical Therapy, 60:1561-1564.
  21. McPoil, T, Brocato, R S. (1985). The foot and ankle: Biomechanical evaluation and treatment. In J. A. Gould, G. J. Davies (Eds.). Orthopaedic and Sports Physical Therapy.St. Louis: Mosby, 313-341.
  22. McPoil, T, Knecht, H. (1987). Biomechanics of the foot in walking: A functional approach. Journal of Orthopedic and Sports Physical Therapy, 7:69-72.
  23. Metzmaker, J. N., Pappas, A. M. (1985). Avulsion fractures of the pelvis. American Journal of Sports Medicine, 13:349-358.
  24. Milgrom, C, et al. (1985). The normal range of subtalar inversion and eversion in young males as measured by three different techniques. Foot and Ankle International, 6:143-145.
  25. Mital, M. A., et al. (1980). The so-called unresolved OsgoodSchlatter lesion: A concept based on fifteen surgically treated lesions. Journal of Bone and Joint Surgery, 62(suppl A): 732-739.
  26. Montgomery, W H, et al. (1994). Electromyographic analysis of hip and knee musculature during running. The American Journal of Sports Medicine, 22:272-278.
  27. Morrison, J. B. (1968). Bioengineering analysis of force actions transmitted by the knee joint. Journal of Biomedical Engineering, 3:164-170.
  28. Murray, M.P., et al (1964). Walking patterns of normal men. Journal of Bone and Joint Surgery, 46A:335-360.
  29. Murray, R, et al. (2002). Pelvifemoral rhythm during unilateral hip flexion in standing. Clinical Biomechanics, 17:147-151.
  30. Murray, S. M., et al. (1984). Torque-velocity relationships of the knee extensor and flexor muscles in individuals sustaining injuries of the anterior cruciate ligament.American Journal of Sports Medicine, 12:436–439.
  31. Nadler, S. F., et al. (2002). Hip muscle imbalance and low back pain in athletes: Influence of core strengthening. Medicine and Science in Sports and Exercise, 34:9-16.
  32. Nadzadi, M. E., et al. (2003). Kinematics, kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation. Journal of Biomechanics, 36:577-591.
  33. Neptune, R R, Kautz, S. A. (2000). Knee joint loading in forward versus backward pedaling: implications for rehabilitation strategies. Clinical Biomechanics, 15:528-535.
  34. Neumann, D. A., et al. (1988). Comparison of maximal isometric hip abductor muscle torques between hip sides. Physical Therapy, 68:496-502.
  35. Nisell, R (1985). Mechanics of the knee: A study of joint and muscle load with clinical applications. Acta Orthopaedica Scandinavica, 56:1-42.
  36. Nissell, R, et al. (1989). Tibiofemoral joint forces during isokinetic knee extension. The American Journal of Sports Medicine, 17:49-54.
  37. Nissan, M. (1979). Review of some basic assumptions in knee biomechanics. Journal of Biomechanics, 13:375-381.
  38. Nordin, M., Frankel, V. H. (1989). Biomechanics of the hip. In M. Nordin & V. H. Frankel (Eds.). Basic Biomechanics of the Musculoskeletal System.Philadelphia: Lea & Febiger, 135-152.
  39. Noyes, F. R, et al. (1980). Knee ligament tests: What do they really mean? Physical Therapy, 60:1578-1581.
  40. Noyes, F. R, Sonstegard, D. A. (1973). Biomechanical function of the pes anserinus at the knee and the effect of its transplantation. Journal of Bone and Joint Surgery, 35 (suppl A):1225-1240.
  41. Nyland, J., et al. (2004). Femoral anteversion influences vastus medialis and gluteus medius EMG amplitude: Composite hip abductor EMG amplitude ratios during isometric combined hip abduction-external rotation. Journal of Electromyography and Kinesiology, 14:255-261.
  42. O'Brien, M., Delaney, M. (1997) The anatomy of the hip and groin. Sports Medicine and Arthroscopy Review, 5:252-267.



  1. Ono, T., et al. (2005). The boundary of the vastus medialis oblique and the vastus medialis longus. Journal of Physical Therapy Science, 17:1–4.
  2. Oshimo, T. A., et al. (1983). The effect of varied hip angles on the generation of internal tibial rotary torque. Medicine and Science in Sports and Exercise, 15:529-534.
  3. Osternig, L. R, et al. (1979). Knee rotary torque patterns in healthy subjects. In J. Terauds (Ed.). Science in Sports.Del Mar, CA: Academic, 37-43.
  4. Osternig, L. R, et al. (1981). Relationships between tibial rotary torque and knee flexion/extension after tendon transplant surgery. Archives of Physical and Medical Rehabilitation, 62:381-385.
  5. Perry, J. (1992). Gait Analysis: Normal and Pathological Function.Thorofare, NJ: Slack.
  6. Polisson, R P. (1986). Sports medicine for the internist. Medical Clinics of North America, 70:469-474.
  7. Porterfield, J. A. (1985). The sacroiliac joint. In J. A. Gould, G. J. Davies (Eds.). Orthopedic and Sports Physical Therapy.St. Louis: Mosby, 550-579.
  8. Pressel, T, Lengsfeld, M. (1998). Functions of hip joint muscles. Medical Engineering and Physics, 20:50-56.
  9. Radakovich, M., Malone, T (1980). The superior tibiofibular joint: The forgotten joint. Journal of Orthopaedic and Sports Physical Therapy, 3:129-132.
  10. Radin, E. L. (1980). Biomechanics of the human hip. Clinical Orthopaedics, 152:28-34.
  11. Rand, M. K, Ohtsuki, T (2000). EMG analysis of lower limb muscles in humans during quick change in running direction. Gait and Posture, 12:169-183.
  12. Raschke, U. Chaffin, D. B. (1996). Trunk and hip muscle recruitment in response to external anterior lumbosacral shear and moment loads. Clinical Biomechanics, 11:145-152.
  13. Reid, D. C., et al. (1987). Lower extremity flexibility patterns in classical ballet dancers and their correlation to lateral hip and knee injuries. American Journal of Sports Medicine, 15(4):347-352.
  14. Roach, K. E., Miles, T P. (1991). Normal hip and knee active range of motion: The relationship to age. Physical Therapy, 71:656-665.
  15. Robbins, S. E., Hanna, A. M. (1987). Running-related injury prevention through barefoot adaptations. Medicine and Science in Sports and Exercise, 19:148-156.
  16. Robinovitch, S. N., et al. (2000). Prevention of falls and fall-related fractures through biomechanics. Exercise and Sport Science Reviews, 28:74-79.
  17. Rodgers, M. (1988). Dynamic biomechanics of the normal foot and ankle during walking and running. Physical Therapy, 68:1822-1830.
  18. Rubin, G. (1971). Tibial rotation. Bulletin of Prosthetics Research, 10(15):95-101.
  19. Salathe, E. P. Jr., et al. (1990). The foot as a shock absorber. Journal of Biomechanics, 23:655-659.
  20. Saudek, C. E. (1985). The hip. In J. Gould, G. J. Davies (Eds.). Orthopaedic and Sports Physical Therapy.St. Louis: Mosby, 365-407.
  21. Savelberg, H. H., Meijer, K (2004). The effect of age and joint angle on the proportionality of extensor and flexor strength at the knee joint. Journal of Gerontology, 59(suppl A), 1120-1128.
  22. Schache, A. G., et al. (2000). Relation of anterior pelvic tilt during running to clinical and kinematic measures of hip extension. British Journal of Sports Medicine, 34:279-283.
  23. Scott, S. H., Winter, D. A. (1991). Talocrural and talocal-caneal joint kinematics and kinetics during the stance phase of walking. Journal of Biomechanics, 24:734-752.
  24. Scott, S. H., Winter, D. A. (1993). Biomechanical model of the human foot: Kinematics and kinetics during the stance phase of walking. Journal of Biomechanics, 26:1091-1104.
  25. Segal, P., Jacob, M. (1973). The Knee.Chicago: Year Book Medical.
  26. Shaw, J. A., et al. (1973). The longitudinal axis of the knee and the role of the cruciate ligaments in controlling transverse rotation. Journal of Bone and Joint Surgery, 56(suppl A): 1603-1609.
  27. Simpson, K J., Kanter, L. (1997). Jump distance of dance landings influencing internal joint forces: I. axial forces. Medicine and Science in Sports and Exercise, 29:916-927.
  28. Slocum, D. B., Larson, R L. (1963). Pes anserinus transplantation: A surgical procedure for control of rotatory instability of the knee. Journal of Bone and Joint Surgery, 50(suppl A):226-242.
  29. Soderberg, G. L. (1986). Kinesiology: Application to Pathological Motion.Baltimore: Williams & Wilkins, 243-266.
  30. Stacoff, A., et al. (2005). Ground reaction forces on stairs: effects of stair inclination and age. Gait and Posture, 21:24-38.
  31. Stergiou, N., et al. (1999). Asynchrony between subtalar and knee joint function during running. Medicine and Science in Sports and Exercise, 31:1645-1655.
  32. Stergiou, N., et al. (2003). Subtalar and knee joint interaction during running at various stride lengths. Journal of Sports Medicine and Physical Fitness, 43:319-326.
  33. Stormont, D. M., et al. (1985). Stability of the loaded ankle. Relation between articular restraint and primary and secondary static restraints. American Journal of Sports Medicine, 13:295-300.
  34. Taunton, J. E., et al. (1985). A triplanar electrogoniometer investigation of running mechanics in runners with compensatory overpronation. Canadian Journal of Applied Sports Science, 10:104-115.
  35. Taylor, W R, et al. (2004). Tibiofemoral loading during human gait and stair climbing. Journal of Orthopaedic Research, 22:625-632.
  36. Tehranzadeh, J., et al. (1982). Combined pelvic stress fracture and avulsion of the adductor longus in a middle distance runner. American Journal of Sports Medicine, 10:108-111.
  37. Tropp, H. (2002). Commentary: Functional ankle instability revisited. Journal of Athletic Training, 37:512-515.
  38. Valderrabano, V., et al. (2006). Ligamentous posttraumatic ankle osteoarthritis. The American Journal of Sports Medicine, 34:612-620.
  39. VanDenBogert, A. J., et al. (1999). An analysis of hip joint loading during walking, running and skiing. Medicine & Science in Sports & Exercise, 31:131-142.
  40. van Ingen Schenau, G. J., et al. (1995). The control of mono-articular muscles in multijoint leg extensions in man. Journal of Physiology, 484:247-254.
  41. Visser, J. J., et al. (1990). Length and moment arm of human leg muscles as function of knee and hip-joint angles. European Journal of Applied Physiology, 61(5-6): 453-460.



  1. Vleeming, A., et al. (1990). Relation between form and function in the sacroiliac joint: Part I. Clinical anatomical aspects. Spine, 15:130-132.
  2. Wallace, L. A., et al. (1985). The knee. In J. Gould, G. J. Davies (Eds.). Orthopaedic and Sports Physical Therapy.St. Louis: Mosby, 342-364.
  3. Wang, C., et al. (1973). The effects of flexion and rotation on the length patterns of the ligaments of the knee. Journal of Biomechanics, 6:587-596.
  4. Wright, D., et al. (1964). Action of the subtalar and ankle-joint complex during the stance phase of walking. Journal of Bone and Joint Surgery, 46(suppl A):361-383.
  5. Yack, H. J., et al. (1993). Comparison of closed and open kinetic chain exercise in the anterior cruciate ligament-deficient knee. American Journal of Sports Medicine, 21:49.
  6. Yates, J. W, Jackson, D. W. (1984). Current status of meniscus surgery. Physician and Sports Medicine, 12:51-56.
  7. Yu, B., et al. (2006). Lower extremity biomechanics during the landing of a stop-jump task. Clinical Biomechanics, 21:297-305.
  8. Zajac, F. E. (2002). Understanding muscle coordination of the human leg with dynamical simulations. Journal of Biomechanics, 35:1011-1018.




Sideways movement of the segment away from the midline or sagittal plane.

Acetabular Labrum

Rim of fibrocartilage that encircles the acetabulum, deepening the socket.


The concave, cup-shaped cavity on the lateral, inferior, anterior surface of the pelvis.


Sideways movement of a segment toward the midline or sagittal plane.

Angle of Anteversion

Angle of the femoral neck in the transverse plane; anterior inclination of the femoral neck.

Angle of Inclination

Angle formed by the neck of the femur in the frontal plane.

Angle of Retroversion

Reversal of the angle of anteversion in which the femoral neck is angled posteriorly in the transverse plane.

Anterior Compartment Syndrome

Nerve and vascular compression caused by hypertrophy of the anterior tibial muscles in a small muscular compartment.

Anterior Cruciate Ligament

Ligament inserting on the anterior intercondylar area and medial surface of the lateral condyle; prevents anterior displacement of the tibia and restrains knee extension, flexion, and internal rotation.

Anterior Tilt

Pelvic movement; superior portion of the ilium moves anteriorly.


Inflammation of the apophysis, or bony outgrowth.

Arcuate Ligament

Ligament inserting on the lateral condyle of the femur and head of the fibula; reinforces the posterior capsule of the knee.


Inflammation of the bursae.

Calcaneal Apophysitis

Inflammation at the epiphysis on the calcaneus.

Calcaneocuboid Joint

The articulation between the calcaneus and the cuboid bones; part of the midtarsal joint.

Calcaneofibular Ligament

Ligament inserting on the lateral malleolus and outer calcaneus; limits backward movement of the foot and restrains inversion.

Calcaneonavicular Ligament

Ligament inserting on the calcaneus and the navicular; supports the arch and limits abduction of the foot.

Chondromalacia Patellae

Cartilage destruction on the underside of the patella; soft and fibrillated cartilage.


A rounded projection on a bone.

Congenital Hip Dislocation

A condition existing at birth in which the hip joint subluxates or dislocates for no apparent reason.


See Sacral Extension.

Coxa Plana

Degeneration and recalcification (osteochondritis) of the capitular epiphysis (head) of the femur; also called Legg-Calvé-Perthes Disease.

Coxa Valga

An increase in the angle of inclination of the femoral neck (>125°).

Coxa Vara

A decrease in the angle of inclination of the femoral neck (<125°).

Deltoid Ligament

Ligament inserting on the medial malleolus, talus, navicular, and calcaneus; resists valgus forces and restrains plantarflexion, dorsiflexion, eversion, and abduction of the foot.

Distal Femoral Epiphysitis

Inflammation of the epiphysis at the attachment of the collateral ligaments at the knee.


Movement of the foot up in the sagittal plane; movement toward the leg.


Eminence on a bone above the condyle.


A limitation in dorsiflexion caused by a short Achilles tendon or tight gastrocnemius and soleus muscles.


Lifting of the lateral border of the foot.


Movement of a segment away from an adjacent segment so that the angle between the two segments is increased.

External Rotation

Movement of the anterior surface of a segment away from the midline; also termed lateral rotation.


A small plane surface on a bone where it articulates with another structure.


Movement of a segment toward an adjacent segment so that the angle between the two is decreased.




Region of the foot that includes the metatarsals and phalanges.

Forefoot Valgus

Eversion of the forefoot on the rear foot, with the subtalar joint in neutral position.

Forefoot Varus

Inversion of the forefoot on the rear foot with subtalar in the neutral position.

Genu Valgum

A condition in which the knees are abnormally close together with the space between the ankles increased; knock-knees.

Genu Varum

A condition in which the knees are abnormally far apart with the space between the ankles decreased; bowlegs.


A group of muscles on the posterior thigh consisting of the semimembranosus, semitendinosus, and biceps femoris.

Head of Femur

The proximal end of the femur, a large, round structure.


Region of foot that includes the talus and calcaneus; also called the rear foot.


Continuation of extension past the neutral position.

Iliac Apophysitis

Inflammation of the attachment sites of the gluteus medius and tensor fascia latae on the iliac crest.

Iliofemoral Ligament

Ligament inserting on the anterosuperior spine of the ilium and intertrochanteric line of the femur; supports the anterior hip joint and offers restraint in extension and internal and external rotation.

Iliotibial Band

A fibrous band of fascia running from the ilium to the lateral condyle of the tibia.

Iliotibial Band Syndrome

Inflammation of the iliotibial band caused by thigh adduction and internal rotation.


The superior bone of the pelvic girdle.

Infrapatellar Bursa

A bursa between the patellar ligament and the tibia.

Intercondylar Eminence

Ridge of bone on the tibial plateau that separates the surface into medial and lateral compartments.

Intercondylar Notch

Convex surface on the distal posterior surface of the femur.

Internal Rotation

Movement of the anterior surface of a segment toward the midline; also termed medial rotation.

Interosseous Ligament

Ligament connecting adjacent tarsals; supports the arch and the intertarsal joints.

Interphalangeal Joint

Articulation between adjacent phalanges of the fingers and toes.

Intertarsal Joint

Articulation between adjacent tarsal bones.


Lifting of the medial border of the foot.

Ischiofemoral Ligament

Ligament inserting on the posterior acetabulum and iliofemoral ligament; restrains adduction and internal rotation of the thigh.


The inferoposterior bone of the pelvic girdle.

Lateral Collateral Ligament

Ligament inserting on the lateral epicondyle of the femur and head of the fibula; resists varus forces and is taut in extension.

Lateral Tibial Syndrome

Pain on the lateral anterior leg caused by tendinitis of the tibialis anterior or irritation to the interosseous membrane.

Legg-Calvé-Perthes Disease

Degeneration and recalcification (osteochondritis) of the capitular epiphysis (head) of the femur; also called coxa plana.

Longitudinal Arch

Two arches (medial and lateral) formed by the tarsals and metatarsals, which run the length of the foot and participate in both shock absorption and support while the foot is bearing weight.

Medial Collateral Ligament

Ligament inserting on the medial epicondyle of the femur, medial condyle of the tibia, and medial meniscus; resists valgus forces and restrains the knee joint in internal and external rotation; taut in extension.

Medial Tibial Syndrome

Pain above the medial malleolus caused by tendinitis of the tibialis posterior or irritation of the interosseous membrane or periosteum; previously called shin splints.


A crescent-shaped fibrocartilage on the articular surface of the knee joint.


Strain of the ligaments supporting the metatarsals.

Metatarsophalangeal Joints

Articulations between the metatarsals and the phalanges in the foot.


Region of the foot that includes all of the tarsals except the talus and calcaneus.

Midtarsal Joint

Two articulations: the calcaneocuboid and the talonavicular joints; also called the transverse tarsal joint.

Morton's Toe

A condition in which the second metatarsal is longer than the first metatarsal.

Neck of Femur

Column of bone connecting the head of the femur to the shaft.


See Sacral Flexion.

Osgood-Schlatter Disease

Irritation of the epiphysis at the tibial tuberosity caused by overuse of the quadriceps femoris muscle group.


Degenerative joint disease characterized by breakdown in the cartilage and underlying subchondral bone, narrowing of the joint space, and osteophyte formation.

Osteochondral Fracture

Fracture at the bone and cartilage junction.

Osteochondritis Dissecans

Inflammation of bone and cartilage, resulting in splitting of pieces of cartilage into the joint.


Triangular sesamoid bone on the anterior knee joint; encased by the tendons of the quadriceps femoris muscle group.

Patella Alta

Long patellar tendon.

Patella Baja

Short patellar tendon.

Patellar Groove

The convex surface on the distal anterior surface of the femur; accommodates the patella; also called the trochlear groove.



Patellar Ligament

Ligament inserting on the inferior patella and the tibial tuberosity; transfers the quadriceps femoris muscle force to the tibia.

Patellofemoral Joint

Articulation between the posterior surface of the patella and the patellar groove on the femur.

Patellofemoral Pain Syndrome

Pain around the patella.

Pelvic Girdle

A complete ring of bones composed of two coxal bones anteriorly and laterally and the sacrum and coccyx posteriorly.

Pelvifemoral Rhythm

The movement relationship between the pelvis and the femur during thigh movements at the hip.


Inflammation of the periosteum that is marked by tenderness and swelling on the bone.

Pes Anserinus

The combined insertion of the tendinous expansions from the sartorius, gracilis, and semitendinosus muscles.

Pes Cavus

High-arched foot.

Pes Planus

Flat foot.

Plantar Fascia

Fibrous band of fascia running along the plantar surface of the foot from the calcaneus to the metatarsophalangeal articulation.

Plantar Fasciitis

Inflammation of the plantar fascia.

Plantarflexed First Ray

Position of the first metatarsal below the plane of the adjacent metatarsal heads.


Movement of the foot downward in the sagittal plane; movement away from the leg.


Ridge or fold in the synovial membrane.

Posterior Cruciate Ligament

Ligament inserting on the posterior spine of the tibia and the inner condyle of the femur; resists posterior movement of the tibia on the femur and restrains flexion and rotation of the knee.

Posterior Oblique Ligament

Ligament inserting on the semimembranosus muscle; supports the posterior medial capsule of the knee joint.

Posterior Tilt

Pelvic movement designated by posterior movement of the superior portion of the ilium.


A triplanar movement at the subtalar and midtarsal joints that includes calcaneal eversion, abduction, and dorsiflexion.

Pubic Ligament

Ligament inserting on the bodies of the right and left pubic bones; maintains the relationship between right and left pubic bones.

Pubic Symphysis

A cartilaginous joint connecting the pubic bones of the right and left coxal bones of the pelvis.


The anterior inferior bone of the pelvic girdle.

Pubofemoral Ligament

Ligament inserting on the pubic part of the acetabulum, superior rami, and intertrochanteric line; restrains hip abduction and external rotation.


The angle formed by the longitudinal axis of the femur and the line of pull of the patellar ligament.

Quadriceps Femoris

A combination of muscles on the anterior thigh, including the vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris.

Rear Foot

Region of foot that includes the talus and calcaneus; also called the hindfoot.

Rear Foot Varus

Inversion of the calcaneus with deviation of the tibia in the same direction.

Retrocalcaneal Bursitis

Inflammation of the bursa between the Achilles tendon and the calcaneus.

Stress Fracture

Microfracture of the bones developed through repetitive force application exceeding the structural strength of the bone or the rate of remodeling in the body tissue.

Subtalar Joint

The articulation of the talus with the calcaneus; also called the talocalcaneal joint.


Triplane movement at the subtalar and midtarsal joints that includes calcaneal inversion, adduction, and plantarflexion.

Sacral Extension

Posterior movement of the top of the sacrum.

Sacral Flexion

Anterior movement of the top of the sacrum.

Sacral Rotation

Rotation of the sacrum about an axis running diagonally through the bone; right rotation occurs as the anterior surface of the sacrum faces right.

Sacroiliac Joint

A strong synovial joint between the sacrum and the ilium.


Inflammation at the sacroiliac joint.


A triangular bone below the lumbar vertebrae that consists of five fused vertebrae.

Screw-Home Mechanism

The locking action at the end of knee extension; external rotation of the tibia on the femur caused by incongruent joint surfaces.

Slipped Capital Femoral Epiphysitis

Displacement of the capital femoral epiphysis of the femur caused by external forces that drive the femoral head back and medial to tilt the growth plate.

Snapping Hip Syndrome

A clicking sound that accompanies thigh movements; caused by the hip capsule or iliopsoas tendon moving on a bony surface.


An injury to a ligament surrounding a joint; rupture of fibers of a ligament.


Injury to the muscle, tendon, or muscle–tendon junction caused by overstretching or excessive tension on the muscle; tearing and rupture of the muscle or tendon fibers.

Talocalcaneal Ligament

Ligament inserting on the talus and calcaneus; supports the subtalar joint.

Talocrural Joint

The articulation of the tibia and fibula with the talus; the ankle joint.

Talofibular Ligament

Ligament inserting on the lateral malleolus and the posterior talus; limits plantarflexion and inversion; supports the lateral ankle.

Talonavicular Joint

Articulation between the talus and the navicular bones; part of the midtarsal joint.



Talonavicular Ligament

Ligament inserting on the neck of the talus and navicular; limits inversion and stabilizes the talonavicular joint.

Talotibial Ligament

Ligament inserting on the tibia and talus; limits plantarflexion and supports the medial ankle.

Tarsometatarsal Joint

Articulation between the tarsals and metatarsals.

Tarsometatarsal Ligaments

Ligaments inserting on the tarsals and metatarsals; supports the arch and maintains stability between the tarsals and metatarsals.


Inflammation of a tendon.

Tibial Plateau

A level area on the proximal end of the tibia.

Tibiofemoral Joint

Articulation between the tibia and the femur; the knee joint.

Tibiofibular Joint (Inferior)

Articulation between the distal end of the fibula and the distal end of the tibia.

Tibiofibular Joint (Superior)

Articulation between the head of the fibula and the posterolateral inferior aspect of the tibial condyle.

Tibiotalar Joint

Articulation between the tibia and the talus.

Transverse Arch

An arch formed by the tarsals and metatarsals; runs across the foot, contributing to shock absorption in weight bearing.

Transverse Ligament

Ligament inserting on the medial and lateral meniscus; connects the menisci to each other.

Trendelenburg Gait

Alteration in a walking or running gait caused by inefficiency in the abductors of the thigh, causing a drop in the pelvis to the unsupported side.

Trochanteric Bursa

A fibrous, fluid-filled sac between the gluteus maximus and the greater trochanter.


Segment angle bowed medially; medial force.


Segment angle bowed laterally; lateral force.