I. Normal Gait
A. Walking is the process by which the body moves forward while maintaining stance stability. During the gait cycle, agonist and antagonist muscle groups work in concert to advance the limb.
1. Most muscle groups undergo eccentric (lengthening with contraction) contractions.
2. The quadriceps undergoes concentric contraction (muscle shortening) during midstance.
3. Alternatively, some muscle groups undergo isocentric contracture (muscle length stays constant). An example of this is the hip abductors during midstance.
B. The gait cycle, or stride (
Figure 1)
1. The gait cycle is the complete sequence of all of the functions of a single limb during walking, from initial contact to initial contact. The sections of the gait cycle are often expressed as a percentage, beginning with initial contact (0%) and ending with the most terminal portion of swing (100%).
2. The gait cycle comprises two periods: stance and swing.
a. Stance—Period while the foot is in contact with the ground. At normal walking speed, stance constitutes approximately 60% of the gait cycle.
b. Swing—Period when the foot is off the ground and the leg is moving forward. Swing constitutes 40% of the gait cycle.
c. The percentage relationship between stance and swing periods is velocity dependent.
3. The gait cycle also can be described in terms of step and stride.
a. Stride is the distance between consecutive initial contacts of the same foot with the ground.
b. Step is the distance between the initial contacts of alternating feet.
4. Three tasks are required during gait: During stance, the leg must (a) accept body weight and (b) provide single-limb support; (c) during swing, the limb must be advanced.
5. Eight phases of the gait cycle
a. Weight acceptance (stance): initial contact, limb-loading response
b. Single-limb support (stance): midstance, terminal stance, preswing
c. Limb advancement (swing): initial swing, midswing, terminal swing
6. Characteristic joint positions and muscle activity during each phase of gait
a. Initial contact: begins as the foot contacts the ground.
i. In normal gait, the heel is the first part of the foot to touch the ground.
ii. The hip is flexed, the knee is extended, and the ankle is dorsiflexed to neutral.
iii. The hip extensor muscles contract to stabilize the hip because the body's mass is behind the hip joint.
b. Loading response
i. Loading response marks the beginning of the initial double-limb stance period.
ii. It begins when the foot contacts the floor and continues until the opposite foot is lifted for swing.
iii. Body weight is transferred onto the supporting leg.
iv. During the loading response, the knee flexes to 15°, and the ankle plantar flexes to absorb the downward force.
v. The ankle dorsiflexor muscles are active with an eccentric contraction (lengthening contraction) to control the plantar flexion moment.
vi. As the knee flexes and the stance leg accepts the weight of the body, the quadriceps muscle becomes active to counteract the flexion moment and stabilize the knee.
[Figure 1. The gait cycle. An example of gait temporal-spatial data depicting the measurement of symmetry and timing.]
c. Midstance
i. Midstance is the initial period of single-limb support.
ii. Midstance begins with the lifting of the opposite foot and continues until body weight is aligned over the supporting foot.
iii. The supporting leg advances over the supporting foot by ankle dorsiflexion while the hip and knee extend.
iv. The hip extensors and quadriceps undergo concentric contraction (muscle shortening) during midstance.
v. As the body's mass moves ahead of the ankle joint, the calf muscles become active to stabilize the tibia and ankle to allow the heel to rise from the floor.
d. Terminal stance
i. Terminal stance begins when the supporting heel rises from the ground and continues until the heel of the opposite foot contacts the ground.
ii. Body weight progresses beyond the supporting foot as increased hip extension puts the leg in a more trailing position.
iii. The heel leaves the floor, and the knee begins to flex as momentum carries the body forward.
iv. In the final portion of terminal stance, as the body rolls forward over the forefoot, the toes dorsiflex at the metatarsophalangeal joints.
v. The toe flexor muscles are most active at this time.
e. Preswing
i. Preswing marks the second double-limb stance interval in the gait cycle.
ii. This phase begins with the initial contact of the previous swing limb and ends with toe-off of the previously supporting leg.
iii. Ground contact by the opposite leg, making initial contact, causes the knee of the trailing limb to flex to 35° and the ankle to plantar flex to 20°.
iv. Body weight is transferred to the opposite limb.
v. The quadriceps should be inactive at this time to allow the knee to flex.
vi. The hip flexor muscles provide the power for advancing the limb and are active during the initial two thirds of the swing phase.
vii. Forward movement of the leg provides the inertial force for knee flexion.
f. Initial swing
i. Initial swing marks the period of single-limb support for the opposite limb.
ii. This phase begins when the foot is lifted from the floor and ends when the swinging foot is opposite the stance foot.
iii. The swing leg is advanced by concentric contraction of the hip flexor muscles.
iv. The knee flexes in response to forward inertia provided by the hip flexors.
v. The ankle partially dorsiflexes to ensure ground clearance.
g. Midswing
i. Midswing begins when the swinging foot is opposite the stance foot and continues until the swinging limb is in front of the body and the tibia is vertical.
ii. Advancement of the swing leg is accomplished by further hip flexion.
iii. The knee extends with the momentum provided by hip flexion while the ankle continues dorsiflexion to neutral.
iv. The ankle dorsiflexors become active during the latter two thirds of the phase to ensure foot clearance as the knee begins to extend.
h. Terminal swing
i. This phase begins when the tibia is vertical and ends when the foot contacts the floor.
ii. Limb advancement is completed by knee extension.
iii. The hamstring muscles decelerate the forward motion of the thigh during the terminal period of the swing phase.
iv. The hip maintains its flexed position.
v. The ankle dorsiflexors maintain their activity to ensure that the ankle remains dorsiflexed to neutral.
C. Center of mass (COM)
1. The COM is located anterior to the second sacral vertebra, midway between both hip joints (
Figure 2).
2. The body requires the least amount of energy to move along a straight line.
3. During gait, the COM deviates from the straight line in vertical and lateral sinusoidal displacements.
a. The COM displaces vertically in a rhythmic fashion as it moves forward.
[Figure 2. Illustration from a sagittal view of the COM and weight-bearing line in the standing position.]
b. The highest point occurs at midstance, and the lowest point occurs at the time of double-limb support.
c. The mean vertical displacement is 5 cm, and the mean lateral displacement is approximately 5 cm.
d. The speed of movement of the COM decreases at midstance, and the peak of vertical displacement is achieved.
e. The speed of movement of the COM increases as the stance limb is unloaded.
f. The COM displaces laterally with forward movement.
g. As weight is transferred from one leg to the other, the pelvis shifts to the weight-bearing side.
h. The limits of lateral displacement are reached at midstance.
D. Gait analysis—A clinically useful way to assess lower limb function either by visual observation or with quantitative measurements.
1. Visual analysis
a. Visual analysis begins with a general assessment, noting symmetry and smoothness of movements of the various body parts.
b. The cadence (steps per minute), base width, stride length, arm swing, movement of the trunk, and rise of the body should be noted.
c. Because of the speed and the complexity of walking, visual analysis does not supply the observer with enough quantitative information to enable precise diagnosis.
d. Videotaping is useful for supplementing clinical observation.
2. Laboratory gait analysis
a. Kinematics is the analysis of the motion produced during the gait cycle (
Figure 3).
b. Kinetics is the analysis of forces that produce motion (
Figure 4).
c. Dynamic polyelectromyography assesses the activity of multiple muscles during gait (
Figure 5).
3. Stride can be assessed with gait pressure mats or other timing devices. Characteristics include velocity, cadence (steps per minute), stance and swing times, and single- and double-limb support times.
4. Kinematic analysis
a. Videotaping in two planes is useful for recording motion.
b. Electrogoniometers or tensiometers are used to record individual joint movement.
c. Motion analysis uses multiple cameras that detect sensors on a patient. The data from the cameras can be used to recreate a three-dimensional model of the patient's gait pattern.
5. Kinetic analysis
a. Force plate studies measure ground reactive forces and changes in the center of pressure as a patient walks.
b. Pedobaric measurements can be used to determine the magnitude and distribution of forces under the foot.
c. Joint moments and powers can be calculated using movement and force data.
6. Dynamic polyelectromyography measures and records the electrical activity in the multiple muscle groups that work during functional activity.
[Figure 3. Three-dimensional sagittal kinematic data of the normal and hemiparetic limbs in the same patient. Data was obtained with CODA mpx motion tracking system (Charnwood Dynamics, Leicestershire, England). Normalized gait cycle expressed as percent of the gait cycle (x-axis); 0 = initial contact, vertical line indicates the beginning of swing phase, 100 = the next initial contact.]
[Figure 4. Kinetic data. Ankle plantar flexion moments of a normal and hemiparetic limb in the same patient.]
II. Pathologic Gait
A. Antalgic gait—Any gait abnormality resulting from pain. It is a nonspecific term. Different pathologies can result in similar compensations during gait.
1. Hip osteoarthritis
a. Leaning of the trunk laterally over the painful leg during stance brings the COM over the joint.
[Figure 5. Dynamic polyelectromyography of the quadriceps muscles obtained from the hemiparetic limb of a patient with a stiff knee gait.]
b. Compressive forces decrease across the joint as the need for contraction of the hip abductor muscles decreases.
2. Knee pain
a. The knee is maintained in slight flexion throughout the gait cycle, especially if there is an effusion.
[
Figure 6. A knee flexion contracture is often associated with a concurrent hip flexion contracture. A crouched posture results in high energy demands because the hip, knee, and ankle extensors must be continuously active to maintain an upright posture. This limits the time and distance a person is able to walk.]
b. Moderate flexion reduces tension on the knee joint capsule.
c. Compensation for knee flexion involves toe walking on the affected side.
d. The time of weight bearing on the painful leg is also reduced.
3. Foot and ankle pain
a. Patients attempt to limit weight bearing through the affected area.
b. The stride length is shortened.
c. Normal heel-to-toe motion is absent.
4. Forefoot pain
a. Patients have a characteristic flatfoot gait.
b. Patients avoid weight bearing on the metatarsal heads.
5. Ankle or hindfoot pain
a. Patients avoid heel strike at initial contact.
b. Patients ambulate on the toes of the affected side.
B. Joint contractures
1. Flexion contracture of the hip
a. The contracture is compensated for by increased lumbar lordosis.
b. Compensatory knee flexion is required to maintain the COM over the feet for stability.
c. The characteristic crouched posture is energy inefficient and results in shorter overall walking distances.
2. Flexion contracture of the knee
a. Flexion contracture of the knee causes a relative limb-length discrepancy.
b. Contractures of less than 30° become more pronounced with faster walking speeds, whereas those of greater than 30° are apparent at normal walking speeds.
c. Gait is characterized by toe walking on the affected side.
d. Increased hip and knee flexion (steppage gait) of the opposite limb may be required to clear the foot because the affected limb is relatively too long (Figure 6).
3. Plantar flexion contracture of the ankle
a. Results in a knee extension moment (knee extension thrust) at initial contact of the forefoot with the floor.
b. During swing phase, hip and knee flexion of the affected limb (steppage gait) must be increased to clear the foot because the limb is relatively too long.
C. Joint instability
1. Knee instability can result in variable gait presentations depending on the ligament involved.
2. Knee recurvatum
a. Knee recurvatum results from weakness of the ankle plantar flexors and quadriceps.
b. During stance, the patient compensates by leaning the trunk forward to place the COM anterior to the knee.
c. This leads to degenerative changes of the knee joint over time (
Figure 7).
[Figure 7. Weakness of the ankle plantar flexors and quadriceps muscles causes a patient to position the COM anterior to the flexion axis of the knee to prevent the knee from buckling. Over time, this compensation leads to a recurvatum deformity of the knee.]
3. Injuries of the posterolateral corner of the knee (posterior cruciate ligament, lateral collateral ligament, posterior joint capsule, and the popliteus tendon) result in a varus thrust gait pattern during stance.
4. Quadriceps avoidance gait
a. This type of gait occurs in patients with an anterior cruciate ligament (ACL)-deficient knee
b. With an ACL-deficient knee, the tibia is prone to anterior subluxation because the contraction of the quadriceps provides an anterior force to the tibia.
c. Attempts to decrease the load response phase on the affected limb are made by decreasing stride length and avoiding knee flexion during the midportion of stance.
[
Figure 8. Assuming a posture of hip flexion places the hip extensor muscles in a position of greater mechanical advantage. This helps to compensate for moderate weakness of the hip extensor muscles (grade 4) during walking.]
5. Ankle instability
a. Ankle instability results in difficulty with supporting body weight during initial contact.
b. An unstable ankle often buckles, resulting in an antalgic gait that limits the load response phase on the affected side.
D. Muscle weakness
1. Weakness of the hip flexor
a. Limits limb advancement during swing
b. Results in a shortened step length
2. Moderate weakness of the hip extensors
a. Compensated by forward trunk flexion
b. This posture places the hip extensors on stretch and in a position of increased mechanical advantage (Figure 8).
3. Severe weakness of the hip extensors results in the need for upper limb assistive devices to maintain an erect posture.
4. Quadriceps weakness
a. Makes the patient susceptible to falls at initial contact
b. The patient compensates by leaning the trunk forward to keep the COM anterior to the knee joint.
c. The gastrocnemius muscle contracts more vigorously to maintain the knee in extension.
d. At times, patients use the hand to push the knee into extension with initial weight bearing.
5. Ankle plantar flexor weakness
a. Causes instability of the tibia and knee as the COM moves anterior to the knee
b. Quadriceps activity increases to keep the knee extended.
c. This compensation limits step length, which predisposes the patient to painful overuse syndromes of the patella and quadriceps.
6. Combined quadriceps and ankle plantar flexor weakness
a. Causes the patient to hyperextend the knee for stability at initial contact
b. Over time, this compensation results in a genu recurvatum deformity.
Top Testing Facts
1. A gait cycle, also known as a stride, is the complete sequence of all the functions of a single limb during walking, from initial contact to initial contact. The sections of the gait cycle are often expressed as a percentage, beginning with the initial contact of the foot with the floor (0%) and ending with the most terminal portion of swing (100%).
2. The sections of the gait cycle—initial contact, single-limb support, etc.—describe the events that occur. The three tasks required during gait are of more conceptual importance, however. During stance, the leg must (a) accept body weight and (b) provide single-limb support; (c) during swing, the limb must be advanced.
3. The normal gait cycle has two periods (stance and swing), and eight phases (initial contact, limb-loading response, midstance, terminal stance, preswing, initial swing, midswing, terminal swing).
4. The COM is located anterior to the second sacral vertebra, midway between the hip joints.
5. Antalgic gait is a nonspecific term that describes any gait abnormality resulting from pain.
6. Flexion contracture of the hip requires compensatory knee flexion to maintain the COM over the feet for stability, resulting in the characteristic crouched posture.
7. A plantar flexion contracture of the ankle results in a knee extension moment (knee extension thrust) at initial contact of the forefoot with the floor.
8. Weakness of the hip flexor limits limb advancement during swing and results in a shortened step length.
9. With quadriceps weakness, the patient compensates by leaning the trunk forward to keep the COM anterior to the knee joint.
10. Ankle plantar flexor weakness causes increased quadriceps activity, limiting step length and predisposing the patient to painful overuse syndromes of the patella and quadriceps.
Bibliography
Crosbie J, Green T, Refshauge K: Effects of reduced ankle dorsiflexion following lateral ligament sprain on temporal and spatial gait parameters. Gait Posture 1999;9:167-172.
Esquenazi A: Biomechanics of gait, in Vaccaro AR (ed): Orthopaedic Knowledge Update 8. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2005.
Gage JR (ed): The Treatment of Gait Problems in Cerebral Palsy Series: Clinics in Developmental Medicine. Mac Keith Press, No. 164.
Keenan MA, Esquenazi A, Mayer N: The use of laboratory gait analysis for surgical decision making in persons with upper motor neuron syndromes. Phys Med & Rehabil State of the Art Revs2002;16:249-261.
Lim MR, Huang RC, Wu A, Girardi FP, Cammisa FP Jr: Evaluation of the elderly patient with an abnormal gait. J Am Acad Orthop Surg 2007;15:107-117.
Neumann DA: Biomechanical analysis of selected principles of hip joint protection. Arthritis Care Res 1989;2:146-155.
Perry J: Gait Analysis: Normal and Pathological Function. Slack Publishers, 1992.