by Shari

Nina asked me to expand a bit on Baxter’s previous post on sacroiliac challenges with asana practice (see Friday Q&A: Sacroiliac (SI) Joint Injuries). I wanted to start by giving a little more background on sacroilac anatomy. As Baxter previously stated, the sacrum is nestled in between the two ilia bones that comprise the pelvis. The front of the pelvis is the symphysis pubis and the back is where the sacrum is located.

The sacrum is affected by many different forces. Along with the pelvis, it forms the bridge between your head, spine, torso and arms with your legs and feet. All forces from the top of your body pass through your sacrum and out to your lower limbs, and at least sixty muscles directly or indirectly affect the sacrum.

However, the sacrum does not move on its own but moves only because of the connections it has to the two ilia bones as well as the muscles that either directly insert onto it or cross over it. This means that the sacrum can only be passively moved. The sacrum’s passive motions caused by muscle action directly onto the pelvis and coccyx (think pelvic floor muscles also) include pivoting (forward and backwards motion) and rocking (spinning on a certain axis).

When you go into a yoga pose, how you set your legs and pelvis up is going to directly affect forces on your sacrum. So if you are turning your pelvis to the right, unless your legs are in the same direction as your pelvis, your sacrum will get conflicting forces through it. There are too many muscles to go into in here, but it’s important to understand that the leg muscles that cross from your pelvis to your femur and the abdominal muscles that attach to your pelvis will have a profound affect on the position of your sacrum. The spine also has a direct effect of moving the sacrum, especially L5 (the lowest of the five lumbar vertebrae) as well as the two ilia bones.

Why the sacrum is so important for yoga students is that we put undue strain on the ligaments that are firmly holding the sacrum in place with the two ilia and on the ligaments that hold the sacrum to the L5 vertebra, particularly when doing asymmetrical poses. And one of the main muscles that has a direct affect on the sacrum is the pesky piriformis. Now why, of all the 66 muscles, am I singling out the piriformis? Well it is one muscle that many yoga students have heard about, and it is one of the main muscles that we stretch when we do Thread the Needle or Figure Four pose. The following figure shows the muscle in red (and you can see how it connects the sacrum and to the leg):

That’s it for now! Tomorrow, we’ll look at how the sacrum and sacroiliac joints work in some typical yoga poses (see Keeping Your Sacrum and SI Joints Happy and Healthy). Hopefully this will provide help for people who are already suffering from sacroiliac joint problems as well as for people who would like to avoid developing problems.

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