The SI Joint
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For some specialists, SI pain is a mysterious phenomenon. Learn some theories about its origin as well as practical ways to help your students prevent or treat SI problems.
If you ask a room full of beginning yoga students where their sacroiliac joints are, most will reply with a blank look that says, “I don’t have a clue.” This is a healthy response–if they don’t know where it is, it probably doesn’t hurt. If you ask a room full of more advanced yoga students–or teachers–the same question, many will immediately start rubbing a bony bump on their lower back, a couple of inches below the belt line and two or three inches to the side of the midline. That’s a pathological response; they rub that spot because it aches. And if you ask a room full of orthopedic surgeons what’s going on with these students and teachers, some will say the ache is coming from a sacroiliac injury, while others will pooh-pooh that idea and insist that the pain is from an injured disk or other spinal problem. What’s going on here?
The probable answer is that in most people (such as beginning yoga students and orthopedic surgeons), the sacroiliac joints don’t move much, if at all. Because of this, beginning students never notice them, and some doctors don’t believe that anything short of a train wreck could push them far enough out of place to cause trouble. In more advanced yoga students and teachers, on the other hand, it appears that these joints often move quite a bit, and they frequently get hurt in the process.
While there is no conclusive, scientific proof that this answer is correct, there is ample medical evidence from the non-yoga world that the sacroiliac joints can indeed move and can be a source of back pain. Regardless of the cause of the all-too-familiar “SI joint” ache in asana practice, yoga teachers have discovered some very effective ways to prevent or relieve it. Let’s start from the beginning and explore this SI phenomenon step-by-step so that you can learn to prevent or treat the problem in yourself or your students.
Where Does it Hurt?
First, let’s make sure we’re all talking about the same thing. If you’ve been around the yoga community long enough, you have heard many yoga students complain of what they call “sacroiliac pain” or “SI pain.” If you question them carefully, you’ll find that this pain usually follows a very specific pattern (described below) that sets it apart from other types of back pain. However, you will also find some students who think they have SI pain when their symptoms don’t fit the pattern, and other students whose symptoms fit the SI pattern but who don’t call their problem by that name.
In this article, we’ll assume that pain that fits the specific pattern below originates in the sacroiliac joints or their surrounding ligaments, even though we acknowledge that some reputable people believe the pain originates elsewhere. It’s very important not to confuse what we are calling SI pain with other types of back pain, because, in most cases, the explanations and suggestions in this article simply don’t apply to students with other types of pain.
The cardinal symptom of SI pain is an ache on or around the posterior superior iliac spine (PSIS), on one side of the body only. The PSIS is the rear-most point of bone on the pelvis. In most students you can palpate it by pressing your fingers into the back of the pelvis above the main mass of the buttock, about two or three inches to the side of the center line of the upper sacrum. If you find it, you will feel a distinct, bony prominence beneath your fingers. If your student tells you that that spot, or the depression just to the inside of it, is achy or tender, while the corresponding spot on the other side of her body is not tender, then she probably has the classic SI problem associated with yoga. (Note that, although your student feels SI pain on or very near the PSIS, this bone actually lies a short distance away from the sacroiliac joint. We’ll look at the anatomy of the joint later.)
If your student does not have pain localized over either PSIS, then she probably does not have an SI problem. For example, some students will report pain localized only on the midline of the sacrum or lumbar spine. Others will report only pain that is clearly above, below or far to the outside of the PSIS. None of these pain patterns is the classic sacroiliac pattern. If your student tells you she has pain over both PSIS bones, her problem is probably either (1) not of sacroiliac origin at all (in which case most of the suggestions in this article probably won’t help), or (2) a complicated problem that may involve one or both SI joints along with other structures (in which case the suggestions in this article may or may not help).
When you find a student with classic, one-sided SI pain, she may tell you that the ache she feels over her PSIS also seems to radiate forward over her pelvic rim, possibly as far as her front groin or upper-inner thigh. She may also report pain that runs down the outside of the hip and leg. It is important to distinguish outer hip and leg pain caused by SI problems from sciatica. Sciatica is pain that follows the course of the sciatic nerve, and it is usually caused by a lumbar disk problem (see Protect the Disks in Forward Bends and Twists). Unlike sacroiliac pain, sciatic pain feels like it passes deep through in the fleshy part of the buttock and travels down the back of the thigh (on the outer side). SI pain emanates from above the buttock and travels only down the side of the thigh, not along the back of it. Also, if your student’s pain radiates all the way to her foot, she would feel sciatica between her first and second toes, whereas she would feel SI pain only on the outer edge of her foot or heel.
Most students with SI problems will tell you that long periods of sitting and most types of forward bends aggravate their pain, but this is also true for students with sciatica and other back problems. And, as with other back problems, backbends can either relieve SI symptoms or make them worse. But unlike students with other back problems, those with SI pain are often particularly aggravated by wide-legged (abducted) poses, such as Baddha Konasana (Bound Angle Pose), Upavistha Konasana (Wide-Angle Seated Forward Bend), Prasarita Padottanasana (Wide-Legged Forward Bend),
Utthita Trikonasana (Extended Triangle Pose), Virabhadrasana II (Warrior II Pose), and Utthita Parsvakonasana (Extended Side Angle Pose). They also have trouble with twists, such as Marichyasana III (Pose Dedicated to the Sage Marichi III), and side-bends, such as Parivrtta Janu Sirsasana (Revolved Head-to-Knee Pose). For many, the worst pose is a combination of twisting, abduction, and forward bending, namely Janu Sirsasana (Head-to-Knee Pose).
Let’s look at the anatomy of the sacroiliac joint to see how it can get injured and what we can do to prevent or relieve trouble there.
Sacroiliac Joint Anatomy 101
A joint is where two bones come together. The sacroiliac joint is where the sacrum bone and the ilium bone join one another.
The sacrum is located at the base of your spine. It is composed of five vertebrae that have fused together during development to form a single bone roughly the size of your hand. When you view the sacrum from the front, it looks like a triangle with its point facing down. When you view it from the side, you see that it curves, concave in front, convex behind, and that it tilts, so its top end is well forward of its bottom end. Protruding from the bottom end of the sacrum is the tailbone (coccyx).
Each half of the pelvis is composed of three bones, the ilium, the ischium and the pubic bone, that have fused together during development. The topmost bone (the one that forms the pelvic rim) is the ilium. The sacrum is wedged between the left and right ilium bones. On the upper part of the sacrum, on each side, there is a rough, rather flat surface that abuts a corresponding rough, flat surface on the ilium. These surfaces are called auricular surfaces. The places where the auricular surfaces of the sacrum and ilium come together are the sacroiliac joints.
The sacrum bears the weight of the spine. The SI joints distribute this weight so that half goes to each hip and, from there, to each leg. As gravity wedges the triangular sacrum firmly down between the inclined auricular surfaces of the ilium bones, it tends to force the ilium bones apart, but strong ligaments prevent them from moving. This wedging action and the resistance of the ligaments combine to form a stable joint.
Some of the ligaments that stabilize the SI joints cross directly over the line where the sacrum and ilium meet. Those on the front are called the ventral sacroiliac ligaments, and those on the back are the dorsal sacroiliac ligaments. Other strong ligaments (the interosseous ligaments) fill the space just above the SI joints, holding the ilium bones firmly against the sides of the upper sacrum. The normal, tilted position of the sacrum places its top end forward of the SI joints and its bottom end behind them. This setup means the weight of the spine tends to rotate the sacrum around the axis formed by the SI joints, pushing the top end down and lifting the bottom end up. The sacrotuberous and sacrospinous ligaments are ideally located to oppose this rotation by anchoring the lower end of the sacrum to the lower part of the pelvis (the ischium bones).
The auricular surfaces of the sacrum and ilium are lined by cartilage. The joint space is completely surrounded by connective tissue and is filled with a lubricating fluid called synovial fluid. Like other synovial joints, the SI joints can move; however, their range of motion is very limited. For example, trained chiropractors, physical therapists and other professionals learn to feel the PSIS tilting back slightly relative to the sacrum when a standing person lifts one knee toward the chest as if marching. This rocking action is thought to aid in walking. However, according to one anatomy text,
The sacroiliac synovial joint rather regularly shows pathologic changes in adults, and in many males more than 30 years of age, and in most males after the age of 50, the joint becomes ankylosed (fused, with the disappearance of the joint cavity); this occurs less frequently in females.¹
In other words, with age, the sacrum and the two ilium bones often merge into a single bone. This might explain why some orthopedic surgeons do not believe in SI joint injury. Perhaps they have operated on adults, seen with their own eyes that the sacrum is completely fused to the two ilium bones, and concluded that even the slightest dislocation of this joint is impossible. This may well be true in people whose joints have fused, but that leaves out the rest of us, more women than men, who, through heredity or lifestyle (including yoga), have retained mobility in our SI joints.
Feeling 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 S.I. Joint 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.
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ABOUT OUR EXPERT
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.