Untuck Your Tailbone for a Healthy SI Joint

I recently wrote a post on the widespread problem of sacroiliac (SI) joint dysfunction among yoga practitioners. In the post, I outlined several causes I’ve observed over 40 years of teaching and practicing yoga asana. In today’s post, we’ll explore how to prevent the first of these causes of SI joint problems.

There could well be more reasons why SI joint dysfunction is common among yoga practitioners that I haven’t yet encountered. (I welcome your thoughts if you’ve experienced SI joint pain from a movement other than the ones I list below.) 

There are certainly other things we do in our daily lives that may cause problems. For example, improper lifting, shoveling snow, and traumatic injuries can destabilize the joint. However, specific actions we practice regularly in yoga can cause SI joint dysfunction.

Here are the ones I’ve identified so far:

• Tucking the tailbone
• Squaring the hips in asymmetrical standing poses such as Trikonasana (Triangle Pose), warrior poses, and twists.
• Too much focus on hip opening

HEALTHY SI JOINT PRACTICE

Untuck Your Tailbone 

The hip system comprises three joints—the hip joints, the SI joint, and the pubic symphysis. The position of each of these joints affects the integrity of the others. (The pubic symphysis is immobile except during birth, so I will focus on the other two here.)

For the sacrum to seat securely in the ilium, it should sit at approximately a 30-degree angle so that the top tilts forward. This means that the pelvic rim needs to tilt forward with the tailbone pointing back. When the sacrum is seated in the joint, the SI joint can perform its main function of transferring force from the legs to the upper body and vice versa. When we tuck the tailbone, we lose that connection. In addition, over time, tucking the tailbone can destabilize the joint as the ligaments that hold the joint together are overstretched.

The sacral/pelvic position has important implications for the SI joint and for the hip joints, as well as the spine and the knees. When we tuck the tailbone, the heads of the femur push up against the anterior rims of the hip sockets. This can wear down the cartilage and labrum of the hip joints over time. In addition, when we tuck the tailbone and push the thigh bones forward, the knees hyperextend. Finally, tucking the tailbone straightens out the lumbar curve.

How to Determine Your SI Joint Position

The most reliable way to know whether your pelvis and, therefore, your SI joint is in a neutral position is to develop an inner reference for what proper positioning feels like. An outside observer, such as a yoga teacher, can’t necessarily judge your position simply by looking at it. This is because the shape of individual sacrum bones is highly variable. Sacrum bones can be wide or narrow, triangular or relatively straight-sided, and the profile of the bone may be curved or straight. So, for example, someone with a curvy sacrum may look as if she is tilting the sacrum forward but may be tucking the tailbone. Here’s an exploration to try:

1. Stand in Mountain Pose (Tadasana) with your feet hip-width apart.
2. Place your fingertips at the top of your thighs, at the hip crease.
3. Tuck your tailbone and palpate the tissue at the hip crease. Note how this tissue feels. It will likely feel taut and hard.
4. Begin to draw the heads of the thighbones back, guiding them gently with your fingertips. You will likely feel as if you’re sticking your butt out.
5. Now, palpate the tissue. If your pelvis is in a neutral position, you will feel a bit of end spring in the tissues at the hip crease. If you tilt too far forward, the tissues will feel slack. So when the tissues feel not too tight or not too loose, you’re probably in the ballpark.

Wag Your Tail for Happy Hips

Another way of determining your sacral position is to check to see if you can “wag your tail,” moving your buttocks side to side.

1. First, stand in Mountain Pose and tuck your tailbone. Try to wag your tail. Your pelvis will likely stay stationary, and your upper body will move side to side.
2. Then, tilt your pelvic rim forward to the point where the tissues in the hip crease feel springy but not slack. Now, try to wag your tail. If you can wag your pelvis from side to side, your pelvis is likely neutral, and your sacrum can sit securely in the joint.

Stay tuned for the next in my SI joint series, where I’ll discuss why not to square your hips in asymmetrical standing poses.