Today I'd like to offer 5 insights about the SI joint (or sacroiliac joint) that we don't tend to learn about in yoga teacher training, but which definitely have implications for how we teach and practice yoga. Also included are multiple scientific references for each point. I invite you to read these points with an open mind and a willingness to possibly question your own biases (because I know I have had to question my own many times as I continue to study and learn about the body!)
Insight #1: The SI joint is a strong, resilient structure that is supported by thick layers of some of the strongest ligaments and muscles in the body. [Ref, Ref, Ref]
Although the SI joints are some of the strongest joints in the body, we often receive the impression from our yoga teacher trainings that they are actually quite fragile structures that are vulnerable to injury and instability from the slightest misalignments in yoga. For example, we are sometimes taught that if we hold our pelvis "square" when we twist in poses like twisting triangle (parivrtta trikonasana), we can "tweak" our SI joints by pulling them out of alignment, and we should therefore instead always be mindful to let our pelvis turn slightly in the direction we are twisting in these poses. Another example is that we are often instructed in backbends like bridge pose (setu bandha sarvangasana) and locust pose (shalabhasana) to relax our glutes (or to at least soften them somewhat) because if we contract them too hard, this could injure our SI joints.
One reason we tend to believe that our SI joints are vulnerable to damage in yoga is that we generally learn about SI joint anatomy by looking at a skeleton model or a drawing like this one here:
When we see the bones by themselves like this, we can certainly get the impression that the sacrum can "slide around" relative to the pelvis easily, resulting in an SI joint that can be pulled "out of place" or "strained" due to small misalignments in yoga poses.
However, what we rarely see after learning about the bony anatomy of the SI joint's structure is an image like this, which depicts all of the extremely resilient, tough ligaments that surround and support the SI joints from all sides, holding them firmly in place:
A rarely-cited fact is that the ligaments of the SI joint include some of the strongest ligaments in the human body! [Ref]
If after seeing an image of the SI joint's ligamentous support, we were then shown an image like this one below, which depicts all of the thick musculature and fascia on top of all of those ligaments on top of the SI joints (including the powerful gluteus maximus, the largest muscle in the human body), we might have reason to be more confident and less fearful about this naturally strong, sturdy area of our body:
While our SI joint can certainly be injured and we can absolutely experience pain there (more on this in #4), it would take much more force to injure a healthy SI joint than the relatively low loads involved in a yoga practice.
The SI joints serve to transfer the load of the upper body to the lower body, as well as to distribute forces moving up the body from below. Therefore, stability is built into their very design so that these forces can be transferred efficiently through the pelvis.
In fact, the SI joints are so inherently stable that there is only the tiniest amount of movement available at these joints. While some sources state that the amount of motion available at the SI joint is a barely-perceptible 2-4 millimeters, other sources actually state that there is in fact no movement available at these joints at all.
Insight #3: Even if the SI joints could "slip out of place" easily, we don't have a reliable way to assess this in someone's body. [Ref, Ref, Ref, Ref, Ref]
SI joint movement is so minute and difficult to identify with either manual palpation or radiographic imaging that none of the tests traditionally done to assess the SI joint have been shown to be reliable. Without an accurate method for testing the position and movement of an SI joint, how can we definitively know that someone's SI joint is "out of place", "misaligned", or "unstable" in the first place?
Insight #4: SI joint pain is certainly a common experience among yogis and non-yogis alike, but SI joint pain does not necessarily mean that there is an SI joint injury. [Ref]
Thankfully, insights from modern pain science are beginning to become more widely known in the yoga world, but if this topic is new to you, consider taking a look at the introduction to pain science article that I wrote for Yoga International a couple of years ago. It turns out that despite what we have traditionally been taught, pain and tissue damage often do not correlate on a 1:1 basis - especially when pain is experienced in a more persistent or chronic way. Pain is actually a much more complex, multi-factorial phenomenon than simply "I have tissue damage and therefore that is what is creating my pain."
As an example, if someone has SI joint pain and they have experienced a recent blunt force trauma to their pelvis region (think from a car accident or a major fall of some sort), then their pain is very likely due to an actual SI joint injury. Once this injury has healed, this pain should subside. In fact, my husband and I suspect that his SI joint may have been injured many years ago in yoga by a strong adjustment he received. His yoga teacher forcefully pulled both of his legs behind his head in a pose called dwipada sirsasana and he felt a searing pain at his left SI joint in that moment. Thankfully the injury healed, but this type of forceful, deep adjustment seems like it was enough to cause injury to his SI joint (or at least a strong protective output of pain in the area).
But in contrast to those examples of short-term pain associated with acute injury, when someone's SI joint pain is more long-term or chronic in nature (chronic pain is sometimes defined as pain lasting longer than 3 months), it's less likely that this pain is connected to a specific injury or damage to the area, and more likely that the person's nervous system is instead sensitive around that spot. Nervous system sensitivity and an output of pain can be the result of many different factors aside from actual tissue damage. Other influences include emotions, past experiences, stress levels, beliefs - and particularly beliefs about one's body. In fact, the more that someone believes that their SI joints are fragile and vulnerable, the more likely their nervous system is to perceive threat in that area and to output pain there. And conversely, the more someone learns that their SI joints are strong, inherently stable structures well-supported by some of the most durable ligaments and muscles of the body, the less likely their nervous system will be to perceive threat and output pain in this area. [Ref, Ref]
Insight #5: Warnings about protecting the SI joint in yoga are often unnecessary.
As we have seen, the SI joints are held stable by a ligamentous and musculature support structure that is strong and resilient - and the joints themselves have only a tiny amount of movement available (if any) in the first place. With this in mind, whether or not we hold our pelvis square when we twist in yoga is probably not a likely mechanism for SI joint injury either way, given the relatively low loads involved in the pose. And whether or not we squeeze our glutes in backbends in yoga is also unlikely to be a mechanism for SI joint injury; in fact, contrary to the common cautions in yoga, contracting our glutes in backbends has actually been shown to have a positive stabilizing effect on the SI joints. [Ref, Ref]
Additionally, it's common these days to hear warnings about "overstretching" the ligaments of the SI joints in yoga poses, leading to SI joint instability and pain. (I myself used to offer such cautions too - the idea just seems to make sense!) We are learning, however, that this is not actually how ligaments respond to stretching. During a stretch, a ligament lengthens temporarily, but then it returns to its resting length afterward (sometimes after a short recovery period.) Despite popular warnings, passive stretching has not been shown to lengthen and destabilize ligaments and joints. I have personally changed my perspective on this issue due to insights from newer research and teachings from my yoga biomechanics mentor Jules Mitchell.
(For more reading on the fascinating topic of stretching, ligaments, and joint instability with lots of research references cited, I encourage you to read this recent blog post by Greg Lehman, a researcher and clinician whose work I have followed and admired for quite some time now. But fair warning: this post is long and is really territory for the more serious body geeks among us. You can always jump right to "Questionable Assertion #3", which specifically addresses these topics and might offer some new, interesting information for you to ponder.)
In summary, SI joint pain is common among yogis and non-yogis alike and there are many factors that can contribute to it, including physical, psychological, and social ones. How we align our body in yoga is probably not a mechanism for SI joint injury, though (strong, forceful adjustments by yoga teachers excepted!) Rather than worrying too much about alignment for SI joint protection, a more effective means to injury-prevention is to simply strengthen and condition the muscles and connective tissue that support the SI joint, so that their capacity to handle load increases.
Thank you for reading these 5 points with an open mind, and I hope to see you on the mat virtually or in person in the near future!