Protect the Sacroiliac JointsFeeling Out of Place
Many health professionals who have worked with yogis believe that the cause of their sacroiliac pain is excessive movement of the joint, leading to misalignment, ligament strain, and, possibly, eventual deterioration of cartilage and bone on the auricular surfaces. There are a number of theories about the details of the pathology. To understand one hypothesis about what SI misalignment means, imagine a piece of china that has broken in two. The broken edge of each piece has a rough surface, but, because they match one another exactly, you can fit the two pieces back together precisely. The bumps on one surface fit into the depressions on the other, and vice versa. When you glue the two pieces back together, all you see is a tiny hairline where the break was. But if you misalign the two pieces in any direction, the bumps on one will clash with the bumps on the other, and the crack between them will remain wide.
Similarly, the auricular surfaces of the sacrum and ilium have bumps and depressions that fit together beautifully when you align them properly but clash with one another if you shift the bones out of place in any direction. In this hypothesis, the pressure of bump on bump is the source of SI pain. If it continues over a long period of time it may eventually cause the cartilage and then the bone to deteriorate, causing more pain.
Since strong ligaments hold together the SI joint, the only way to move it out of place with yoga is to overstretch those ligaments. So another hypothesis is that the source of SI pain is sprained or torn ligaments, rather than injury to the joint surfaces themselves. Of course, the two hypotheses are not mutually exclusive; on the contrary, it seems likely that an extreme stretch could simultaneously damage ligaments and move the joint out of alignment.
Why would the SI joint move excessively in more experienced yoga practitioners and teachers, but not in most beginners or other people? Obviously more advanced yogis perform more extreme stretches and repeat them over a longer period of time. But self-selection may also be a factor: a lot of people choose to start and stick with yoga because they are already naturally flexible. So, for pre-existing biological reasons (such as genetic or hormonal differences), many dedicated practitioners may have come to yoga with looser ligaments and muscles than other people, putting them at increased risk of SI instability. Similarly, the high proportion of women in yoga could contribute to the high proportion of SI problems. Women are more susceptible to sacroiliac trouble than men for several reasons. For starters, the width and structure of the female pelvis makes the SI joint less stable in women. Next, women (on average) have more flexible ligaments than men. Finally, women who have been through childbirth sometimes have SI damage because a hormone of pregnancy (relaxin) dramatically loosens ligaments all over the body and the process of childbirth puts enormous strain on the SI joints.
But clearly, we can't blame it all on heredity, hormones, and hard labor. Yoga postures do contribute to sacroiliac problems. What causes the trouble, and what can we do about it?
Getting ahead of Yourself
No one knows for sure, but it appears that in yoga, the most common SI problem occurs when the top of the sacrum tilts too far forward on one side of the body relative to the ilium. This may happen, for example, in asymmetrical forward bends like Janu Sirsasana. Your student's bent leg holds one side of her pelvis back while she uses her arms to pull her spine toward her other leg. The spine pulls the top of her sacrum forward on both sides, but the top of the pelvis (the ilium) stays farther back on the bent leg side, so the top of the sacrum separates from the ilium and moves in front of it on that side.
Something similar can happen when students practice two-leg forward bends, like Paschimottanasana (Seated Forward Bend), unevenly. For example, if your student's right hamstring muscles are tighter than her left ones, when she bends forward in Paschimottanasana her right sitting bone will stop lifting before her left. This will cause her right ilium to stop tilting forward before her left. As her spine bends farther forward, it will drag the top of her sacrum along with it. This will pull the right side of her sacrum forward of her ilium, which is tilted to its maximal point, unseating her SI joint on that side and overstretching the surrounding ligaments. Meanwhile, her left ilium will keep moving forward along with the left side of her sacrum, so she won't put undue stress on her left SI joint.
Even if she practices Paschimottanasana perfectly symmetrically, your student's forward bending action will still stretch her SI ligaments (including the sacrotuberous and sacrospinous ligaments, which normally resist the forward tilt of the sacrum by stopping the lower end from lifting up). This will loosen both of her SI joints, making them more vulnerable to displacement in other poses. If she has loose pubococcygeus muscles (the muscles that run between pubic bone and tail bone), this may make the problem worse by making it easier for the tail bone end of the sacrum to lift up.
Once your student tilts one side (or both sides) of her sacrum too far forward, it tends to get stuck there. The sacrum is narrower in the back than in the front, so as it moves forward, the ilium bones move closer to one another. To slide her sacrum back into place, your student has to force her ilium bones apart against the resistance of the ventral, dorsal, and interosseous sacroiliac ligaments. This is especially hard because it also requires that she slide the bumpy joint surfaces of her sacrum and ilium over one another. This may be why backbending postures sometimes hurt when the SI joint is out of place (she presses bump on bump), but also why backends sometimes relieve SI pain (it feels good if she succeeds in getting the sacrum back where it belongs).
So backbends can be good or bad for the SI joints, while forward bends usually spell trouble. Postures that spread the thighs wide apart (into abduction), like Baddha Konasana, Upavistha Konasana, and Virabhadrasana II are also big time troublemakers. These poses all pull on the adductor (inner thigh) muscles, drawing the pubic bones away from one another. This action apparently pulls apart a critical portion of the SI joints (perhaps it opens the front of the joints more than the back, or opens the lower part of the joints more than the upper part). As the joints unlock, it is easier for the sacrum to slip forward out of place. Loose pelvic floor muscles may aggravate this problem because they allow the left and right halves of the lower pelvis to move away from one another more easily than tight muscles do.
If the above reasoning is correct, then combining abduction with forward bending should be especially hard on the SI joints. The evidence seems to bear this out: people with SI problems often find it puts their SI joint "out" if they bend forward in spread-leg poses like Baddha Konasana, Upavistha Konasana, or Prasarita Padottanasana.
Twists and side-bending postures can also cause trouble for people with unstable SI joints. Twists (like Marichyasana III) can pull one side the sacrum forward of the other. Side bends (like Utthita Trikonasana, Utthita Parsvakonasana, and Parivrtta Janu Sirsasana) may create a gap in the joint on one side and jam it on the other. While side bending alone is unlikely put the joint out of place, the gapping it causes can further loosen an already overstretched interosseous ligament, and the jamming it causes can further irritate misaligned auricular surfaces by pressing them harder against one another.
To round out the picture, imbalances in hip flexor muscles may also contribute to SI problems. The two psoas muscles connect the front of the lumbar spine to the upper inner thighbones. If one of them is tighter than the other, it might pull one side of the spine too far forward, pulling that side of the sacrum along with it. The two iliacus muscles connect the front of the ilium bones to the upper inner thighbones. A tight iliacus on one side could cause a different kind of SI problem by pulling the ilium too far forward relative to the sacrum.
Luckily, SI problems can be avoided. Read Practice Tips for the Sacroiliac Joints for specific asana advice that will help keep your teaching safe.
¹Hollinshead, WH. Textbook of Anatomy. Second Edition. New York: Harper and Row, 1967, p. 378.
Roger Cole, Ph.D. is an Iyengar-certified yoga teacher and Stanford-trained scientist. He specializes in human anatomy and in the physiology of relaxation, sleep, and biological rhythms. Find him at rogercoleyoga.com.
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