BODY AND SOUL ARE NOT TWO SUBSTANCES BUT ONE. THEY ARE MAN BECOMING AWARE OF HIMSELF IN TWO DIFFERENT WAYS.
—C. F. VON WEIZSACKER
THE PYRAMID-SHAPED SACRUM is the site where the vertebral column (sacrum) and pelvic girdle (ilium) intersect. This is the site of union between the upper and lower body, and it functions as a large part of the posterior wall of the pelvis. The sacroiliac joint is a frequent site of problems for practitioners of asana. This chapter explains why.
BONES
The sacrum is created by the fusion of five vertebrae (Figure 7.1; see the sagittal view at Figure 3.1). This fusion is not complete until after the twenty-fifth year of life. The degree of curve of the sacrum bone is about the same as that of a saucer, with the concavity facing anteriorly.
The superior sacrum, sometimes called the base of the sacrum, has two oval superior facet surfaces that articulate with the fifth lumbar vertebra facets. These sacral facet surfaces face posteriorly and oppose the lumbar facets, which face anteriorly.
7.1 ANTERIOR SACROILIAC JOINT
The anterior surface of S1, called the sacral promontory, protrudes into the pelvic cavity. One can note as well the existence of transverse ridges on the anterior sacrum, which identify where the five vertebrae were fused together. On the posterior surface of the sacrum are a series of ridges that run vertically. These are called the middle sacral crest, which has tubercles—the intermediate crests and the lateral crests—that are like primitive spinous processes. Lateral to the intermediate crest are openings for the passage of nerves.
At the distal end of the sacrum, which is called the apex, is the coccyx bone. It is made up of three to five bones that are fused together. This bone serves as the site of muscle and ligament attachment.
JOINTS
It would seem that something as concrete as a joint in the human body could not be controversial. However, there has been debate about whether the sacroiliac joint moves at all and, if so, how much. But as many yoga students can testify, this joint definitely moves. Furthermore, yoga students know that if the sacroiliac joint if is not moving according to anatomical principles (discussed later in this chapter), it can cause discomfort not only during asana practice but also during the activities of daily life.
The sacroiliac joint (SI joint) consists of the union of the convex surface of the sacrum and the concave surface of the ilium. Both joint surfaces are covered with a thin plate of cartilage. In later life, the space of the joint is filled with synovial fluid and thus acts as a gliding joint. The joint surfaces join such that the sacrum is at a diagonal angle of approximately 30 degrees from the vertical, with the promontory anterior and coccyx posterior. The neutral position of the sacrum in standing is not vertical. When your student stands with her sacrum vertical, she is not standing in the neutral position for the sacroiliac joint.
The most important thing to remember about the sacroiliac joint is that its major function is stability. There is definitely some movement needed at the sacroiliac joint, but it is quite minimal. When this stability is disturbed, and the bones are no longer in their neutral position but are separating slightly, the ligaments around the joint are stressed, and discomfort or pain can result.
To help create this stability, the sacroiliac joint surfaces are shaped to facilitate the wedging of the sacrum down into the ilia of the pelvis during weight bearing. When standing, the incumbent weight of the trunk forces the sacrum into the pelvis. This pressing down of the sacrum helps to create stability at the joint by keeping the ilia and sacrum in close proximity. This is called a self-locking mechanism.
Thus stability in the joint is greatest when standing. An unlocking motion occurs when one sits down. This occurs in part because the abdominal muscles are less active as support during sitting, and the sacrum is not wedged as firmly down in the pelvis as during standing.
There are significant gender differences in the structure of the SI joint that contribute to a greater instability in the joint for women. These differences are related to the need for an obstetric pelvis in women. The first structural difference is that the female joint generally has a smaller and flatter surface for joint articulation. Second, the female joint often articulates at only two segments with the pelvis, instead of at three for the male. This lesser degree of congruence at the joint surfaces decreases stability. Additionally the female sacral ligaments are subject to softening during the hormonal changes that accompany menstruation, pregnancy, and lactation. Finally there is additional strain on the female sacroiliac joint during walking. Here is how the strain happens.
The female acetabula are wider apart than the male acetabula in a proportional body. The wider the acetabula are apart, the greater the torque across the sacroiliac joint during each step of walking. To visualize this, hold a towel in front of you with your hands wide apart. Now move one hand forward, as if your hand were your acetabulum in walking. Note the torquing and twisting throughout the length of the towel. Now move your hands closer together; when you “walk” this time, there will be less torque. This is exactly what happens in the female pelvis: each step has a greater chance of stress across the SI joint. All of these factors contribute to the more frequent dysfunction of the sacroiliac joint in females.
7.2 ANTERIOR SACROILIAC JOINT, WITH ANTERIOR LIGAMENTS ON ONE SIDE
7.3 POSTERIOR SACROILIAC JOINT, WITH POSTERIOR LIGAMENTS ON ONE SIDE
CONNECTIVE TISSUE
The function of the sacral ligaments, like all other ligaments in the body, is to provide support for joints. It is especially important that the sacroiliac ligaments are not overstretched in the practice of asana. Once these ligaments are overstretched, not only do they no longer provide the support necessary, but the overstretched ligaments never go back to their previous state. Remember that the main function of the sacroiliac joint is one of stability, not mobility.
Three ligaments support the sacroiliac joint:
▶ The anterior sacroiliac ligament connects the anterior sacrum to the medial ilium. It is broad and flat and is stretched on external rotation of the hip joint (Figure 7.2).
▶ The posterior sacroiliac ligament is one of the strongest of the area. One part runs from the dorsum of the sacrum to the tuberosity of the ilium; the other part runs obliquely from the third tubercle of the posterior sacrum to the posterior superior spine of the ilium (Figure 7.3).
▶ The interosseous sacroiliac ligament connects the tuberosity of the sacrum and the ilium.
These ligaments connect the sacrum and ischium:
▶ The sacrotuberous ligament connects the posterior inferior spine of the ilium, the lateral margin of the sacrum, and the coccyx and the tuberosity of the ischium.
▶ The sacrospinous ligament connects the lateral sacrum and coccyx to the spine of the ischium.
NERVES
The sacral plexus is formed by nerve roots from the lumbar, sacral, and coccygeal areas. The first of these nerves is L4 and the last is C1. The L4-S3 nerves converge and exit the pelvis as the sciatic nerve. For more details about the sacral plexus, see chapter 6.
MUSCLES
One of best ways to create stability in a joint is to strengthen the muscles that cross that joint. Unfortunately, there is only one muscle that crosses the sacroiliac joint, the piriformis. While it is technically considered a muscle of the hip joint, it is included here because of its effect on the sacroiliac.
The piriformis originates from the anterior sacrum, between the first four sacral foramina, and it inserts into the top of the greater trochanter. The muscle lies almost horizontal. When it contracts, it acts as an external rotator of the hip and aids in adduction and extension. Additionally it can help to stabilize the pelvis during walking.
Remember that the sciatic nerve passes under the piriformis, or is sometimes intertwined in it, on its way to exit the pelvis. Therefore a tight piriformis muscle can press on the nerve. This pressure can cause pain along the path of the sciatic nerve—sciatica—which is called piriformis syndrome. See chapter 8 for a stretch for this muscle.
KINESIOLOGY
Mechanics of the Sacroiliac Joint. The entire vertebral column is balanced on the sacrum. In fact, the crucial mechanical joint of the spine is L5-S1. Due to the opposite curves of the lumbar spine and the sacrum, there is an increased shearing stress at the lumbo-sacral angle. This is the shearing stress of the incumbent weight of the column pushing anteriorly, due to the angle of L5 as it joins S1.
The facets of L5-S1 are in a weight-bearing position. When standing, L5 would move forward on S1 due to gravity except for the angle of the facets, as detailed in the Bones section of this chapter. The angle of the L5 and S1 facets create a braking effect on the vertebral bodies to keep L5 from sliding forward on S1. This can contribute to a compression of the articular synovial linings at this level.
While the primary function of the sacroiliac joint is stability, some passive joint movements occur there. The first of these movements is nutation, from the Latin nutare, meaning “to nod” (Figure 7.4). Nutation refers to the movement of S1 in relationship to the lumbar spine and the pelvis; it is the anterior movement of S1 that accompanies lumbar extension. This means that when you back bend your lumbar spine, your S1 vertebra passively moves anteriorly. The opposite movement is counternutation, which is the passive movement of S1 posteriorly, when you perform flexion of your lumbar spine (Figure 7.5).
It is important to understand the relationship of the movements of the lumbar spine and the sacrum. When you perform a back bend—perform active spinal extension—your sacrum passively nutates, and S1 moves anteriorly. When you forward bend—perform active spinal flexion—your sacrum passively counternutates, and S1 moves posteriorly. Nutation and counternutation are passive movements only but they must accompany extension and flexion, respectively, for them to be normal, healthy, and complete.
These movements of extension with nutation and flexion with counternutation are called the lumbo-sacral rhythm. To experience this, stand near a chair and put your hand over your sacrum, which is located just below your waist and is hard and curved outward. Now sit down slowly, and notice how your S1 counternutates as you sit. In other words, your S1 moves posteriorly at exactly the same time that your lumbar spine flexes. Once you have sat down, notice that S1 will move back to its more neutral and slightly nutated position if you sit with your spine long and lifted, with neutral spinal curves.
To complete the experiment, keep your hand on your sacrum and stand up. You will notice the rhythm in reverse. As you begin to stand, your sacrum will nutate as you lean forward and then move slightly back toward counternutation as you come to a neutral standing position. This is normal lumbo-sacral rhythm. If you have some form of sacroiliac dysfunction, this rhythm will be disrupted. It is sometimes possible to guess the cause of a student’s back pain: students with discogenic lower back pain will usually prefer standing to sitting, because sitting increases the pressure on the disc. But students with sacroiliac dysfunction will usually have the most trouble during the transitional movements, from sitting to standing, and vice versa.
7.4 (FAR LEFT) NUTATION
7.5 (LEFT) COUNTERNUTATION
Sacroiliac and Iliosacral Dysfunctions. The way to avoid creating dysfunction at the sacroiliac joint is to move in such a way that the sacrum and pelvis always move together. This is true for all asana movements, especially twists and forward bends.
There are two major dysfunctions at the sacroiliac joint. One is the movement of the sacrum in relationship to the ilium, called sacroiliac dysfunction. The second is iliosacral dysfunction, which is the displacement of the ilium in relationship to the sacrum.
Please understand that these are relative terms; nevertheless there is a difference in the two dysfunctions. Sacroiliac dysfunction is related to the spine itself being stuck at the sacrum level in relationship to the pelvis. Iliosacral dysfunction is the pelvis moving in relationship to the sacrum and is more affected by the muscles of the legs and pelvis pulling on one of the ilia. One of the causes of these dysfunctions can be postural habits, which are almost always asymmetrical for the pelvis, either standing, sitting, or sleeping postures.
Sacroiliac dysfunction specifically is a rotation of the sacrum in relationship to the ilium. This is more related to how the spine is used in relationship to the ilium. Once again, sacroiliac dysfunction can be created by asymmetrical postural habits, in this case of the sacrum. Both of these dysfunctions can be created by the way certain asana are performed, especially twists of all kinds and seated forward bends. When you move your spine in a twisting motion, for example, while keeping your pelvis fixed and still, you are creating a stress at the SI joint and can create sacroiliac dysfunction.
Iliosacral dysfunction is either an anterior or posterior positional fault of the ilium in relationship to the sacrum. Thus the ilium can be rotated and stuck either anteriorly or posteriorly in relationship to the sacrum. An anterior rotation is called anterior torsion, and a posterior rotation is called posterior torsion (Figures 7.6 and 7.7). Remember, the term torsion refers specifically to the movement of the ilium in relationship to the sacrum. This usually happens on one side or the other. Because the acetabulum is on the lateral side of each ilium, by the movement of the acetabulum either anteriorly or posteriorly, a torsion can affect the placement of the femur.
If a student complains of a short leg on the right, for example, three different things could be causing it. First, she could actually have an anatomically short leg, which is the least common reason. The next reason could be that she has a posterior torsion on the right side. Remember, this means that her right ilium is rotated posteriorly. As it rotates posteriorly, it draws the acetabulum posteriorly as well, in effect shortening the right leg. The third reason that her right leg could appear short is that the left ilium is rotated anteriorly. In this case, technically she would not have a short leg but rather a long leg, because she has an anterior torsion right, making her left leg appear longer than her right one.
If you ascertain that the short leg is created by the second reason, that is, a torsion of the ilium, you can have her twist in such a way as to bring her ilum back into place. For example, if she has a left posterior torsion, have her twist for twice as long to the right as to the left in a pose like Marichyasana III, thus encouraging her left pelvis to rotate forward.
7.6 (RIGHT) ANTERIOR TORSION OF THE ILIUM
7.7 (FAR RIGHT) POSTERIOR TORSION OF THE ILIUM
EXPERIENTIAL ANATOMY
For Practicing
7.8 DHANURASANA
Applied Practice 1: Dhanurasana
Props: 1 nonskid mat • 1 blanket
Take Care: Do not practice these poses while pregnant, or when diagnosed disc disease, spondylosis, or spondylolisthesis is present.
BEGIN BY LOCATING your sacrum with your hand. When you are ready for back bends in your practice, fold your blanket in half and then in half again, and place it on your mat. Lie on your belly (unless you are pregnant). Take a moment to place your hand over your sacrum again, to be sure of its location.
Stretch out first one leg and then the other to lengthen the abdomen and upper thigh area. Bend your knees one by one and clasp the ankles. With an exhalation, lift up into Dhanurasana (Figure 7.8). Pay attention to what happens to the sacrum as you do this. It will be nutating S1 down toward the mat as your lumbar spine extends. Hold for a few breaths and come down, resting a moment before repeating.
This time, focus your attention on the S1 vertebra. Reach back and place your fingers on S1 to remind yourself exactly where it is in your body. Now, as you exhale and lift up into the pose again, consciously press S1 to the floor and imagine that everything else is lifting upward. With this thought, you are consciously facilitating nutation. Remember, nutation must accompany extension if extension is to be healthy. Try this pose one more time, again focusing on nutation.
When done, rest for a few cycles of breath and proceed to Practice 2.
7.9 URDHVA DHANURASANA
Applied Practice 2: Urdhva Dhanurasana
Prop: 1 nonskid mat
Take Care: Do not practice these poses while pregnant, or when diagnosed disc disease, spondylosis, or spondylolisthesis is present.
AS YOU ARE READY, turn over and lie on your back for Urdhva Dhanurasana (Figure 7.9). Place your feet near your buttocks, with your toes turned inward; place your hands directly beneath the socket of the shoulder joint, with your fingers turned outward. Exhale, and bring your lower back to the floor so you are in flexion and counternutation. With the next exhalation, move your pelvis out and up and over your feet, in a strong and fairly quick movement. Be sure to lead with your tailbone to stretch out, as if moving the tailbone along the inner thighs.
In the first part of coming up into Urdhva Dhanurasana, you will be keeping your spine in flexion, but this will change about halfway up. Pay attention as you go up to the exact point where the lumbar spine begins to extend and your sacrum begins to nutate. As you straighten your arms and legs, consciously lift the pose, but not from the coccyx. If you lift from your coccyx, that would be counternutation and the opposite of the nutation needed for extension. Rather, lift from S1 to facilitate nutation, so your coccyx actually goes down in relationship to your S1 vertebra.
Many yoga students are taught to lift from the tailbone in this pose, but that is kinesiologically illogical. Extension and nutation go together as natural movements in your body. If you want to facilitate extension, you need to nutate as you lift into the last half of the pose.
Hold the pose for several breaths and keep lifting from your S1 vertebra. Visualize connection between your coccyx and your heels as they both move down. Make sure your feet stay parallel and your inner thighs rotate inward and downward. Come down, rest, breathe, and repeat before moving to the next pose in your practice.
For Teaching
7.10 TADASANA
Applied Teaching 1: The SI Joint in Tadasana
Prop: 1 nonskid mat
Take Care: Stand on an even surface.
HAVE YOUR STUDENT stand on his mat in Tadasana (Figure 7.10), and walk all the way around him, observing his pelvic and sacral positions. Remember that a neutral sacrum is diagonal and not vertical.
After asking permission to touch, first place your flat hands on his iliac crests to ascertain if they are level with the floor. The crests are, of course, curved bones, and so your hands will not be resting on completely flat surfaces. Rather, try to imagine a line tangential to the highest point of the crest and guess whether that line is parallel to the floor. Do not be discouraged if this is not easy to discover at first; just keep practicing it with your students or willing family members. This position is the neutral position of the pelvis.
Once you find the neutral position of his pelvis, begin to note the angle of the sacrum. It should be diagonal and not vertical. If the sacrum is vertical, it has become unlocked from the ilia, and this creates a less stable relationship at the bottom of the column. In order to lock the sacrum into the ilia, the student needs to stand with his sacrum in that 30-degree diagonal line; when he does so, the tops of his ilia will be parallel to the floor as well. Note: this is nota movement created by tucking the tailbone, which is sometimes recommended.
7.11 JANU SIR SASANA
Applied Teaching 2: The SI Joint in Janu Sirsasana
Prop: 1 nonskid mat • 1 towel
Take Care: Do not practice this pose if it causes pain in your sacroiliac area.
HAVE YOUR STUDENT practice the seated forward bend, Janu Sirsasana (Figure 7.11). Ask her permission to touch her. Then kneel behind her and feel her ilia and her sacroiliac joint. This pose is an asymmetrical one and therefore can cause torque at the sacroiliac joint. Make sure that she rolls forward into the forward bend, especially from the ilia of the bent knee side. In other words, have her create the forward bend not by bending over her straight leg but rather by reaching and bending forward from the bent knee side ilium, thus reducing the torque over her SI joint.
Many students stretch forward from the spine of the bent knee side, but this tends to separate the vertebral column/sacrum from the pelvis, which is left behind by this focus. Instead, make sure your student bends forward from the pelvis itself around the concavity of the femoral head to move the ilium, sacrum, and column together. To add some extra help, wedge the edge of a folded towel under the upper, outer area of the back thigh of the bent leg.
7.12 MARICHYASANA III
Applied Teaching 3: The SI Joint in Marichyasana III
Prop: 1 nonskid mat
Take Care: Do not practice this pose if it causes pain in your sacroiliac area.
WHEN YOUR STUDENT practices Marichyasana III, make sure that he begins the twist from his pelvis (Figure 7.12). In other words, make sure that he moves his straight leg forward on the floor, so that the hip socket of the straight leg is several inches, maybe even as many as 6 inches, ahead of the hip socket of the bent knee. This action will create the twist at the very base of the pose. Do not allow him to keep his acetabula even. This will cause the twist to come at the SI joint, thus separating or straining the SI joint. Instead, make sure he moves his straight leg forward, thus beginning the twist from the pelvis, not the sacrum.
If he begins the pose by anchoring his pelvis before twisting, he will in effect be pulling his spine and sacroiliac joint into the twist, while turning his pelvis back in the other direction. Remember, when the sacrum and ilia move in separate directions, this is the definition of sacroiliac dysfunction. Be sure that the student moves his pelvis as the basis of this and all twists.
LINK
While it may seem counterintuitive, those suffering with persistent posterior torsion of the ilia often feel relief when they wear shoes with a slight heel. Suggest to students with posterior torsion that they experiment with wearing shoes with heels one to one and a half inches high instead of flat shoes. (Men can wear boots.) This slight lift can help to create a lumbar curve. This curve will help to rotate the posterior ilium anteriorly, thus bringing it into a more normal position.