The SI Joint: Function and Thoughts
A couple of months ago, I met with a woman I will call Meredith. Meredith is in her early fifties, fit, and energetic. She practices yoga, does ballet and Pilates, and lifts weights regularly once or twice a week. At first glance, she looked like the epitome of health.
Meredith made the appointment with me after following my work for a long time because she thought maybe I could help. She struggled with chronic low back pain around the right SI joint. The pain had been persistent for decades, sometimes a dull ache, sometimes more, but always there, hovering in the background.
When she came to see me the second time, her eyes welled with tears for a brief moment as she told me how much better she had been feeling. She felt for the first time like she had tools to help her when her pain began to settle in. She had been paying more attention to her habits and was regaining a sense of control over her body. She was even experiencing moments when the pain was completely gone.
Meredith’s case was unusual in that she was hyper vigilant with exceptional body awareness, but the basic principles surrounding the SI joint, how it functions, and what happens when there is persistent discomfort remain the same. Understanding the basic anatomy is helpful when helping people feel and assess their patterns. Let’s look at this more closely.
Anatomy of the Pelvis (the abbreviated version):
Your pelvis is comprised of two sides, a left side and a right side. Each side of the pelvis (aka hemipelvis) consists of three bones: the ilium, ischium, and pubis. The back of the pelvis is the sacrum which consists of five fused vertebrae, each side of which connects to the pelvis at the ilium, aka the sacroiliac joint. To be clear, you have two ilia and thus, two sacroiliac joints.
The sacrum connects to the rest of the vertebral column at the lumbosacral joint. The lumbar vertebrae are the largest of the segmented vertebrae, designed to withstand load. Due to their shape and structure, they are naturally good at flexion and extension, less good at rotation.
“But wait,” you might be thinking, “the vertebrae have to rotate because the pelvis rotates during walking gait.”
Indeed, the pelvis does rotate when you walk. This is the result of multi-planar movement at a variety of joints. The sacroiliac joints are stable and, with the pubic symphysis (the connection point between the two pubic bones) create a closed chain that results in a small amount of translation and rotation (Lewis et al., 2017). This results in rotation at the lumbosacral joint and translates into small amounts of rotational movement throughout the lumbar spine as load moves up the kinetic chain (Rice et.al, 2004, Feipel et al., 2001). In fact, Rice et al., found most of the movement that occurred during the lumbar spine during normal gait occurred in the transverse plane and Feipel et al., found walking did not exceed 40% of maximal active ROM in the lumbar spine. What this means is rotation at the lumbar spine isn’t bad; in fact, it’s necessary for normal walking. It also means walking is a safe activity that doesn’t stress the neuromuscular system, (usually) making it a good option for people with low back pain.
Unsurprisingly, movement in the lumbar spine appears to increase as walking speed increases. You can try this on yourself. Walk slowly, as though you were walking through a grocery store or museum. How much movement do you feel through your pelvis and spine? Now, walk quickly, as though you were trying to cross the street before the light turns yellow. How much movement do you feel in your spine now?
The rotation that occurs in the pelvis will be predicated on what happens in the hip. The ilium, ischium, and pubis meet to form the acetabulum, the concavity in the pelvis where the femur sits. As the foot comes into contact with the ground during the stance phase of gait, the pelvis rotates over the femur; as the foot leaves the ground, the femur rotates around the pelvis. In order to transfer force from the leg to the spine and bear the weight of the upper body, the SI joints must be able to permit stable, but flexible, support (Vleeming et al., 2012).
The hip, of course, is dependent on how the foot interacts with the ground and the position of the pelvis is dependent on the position of the thorax above it. Like all things concerning movement, when there is pain or discomfort at one area, it’s important to look above (and below) the painful structure for clues regarding how load is being dispersed throughout the body.
When SI Joint Pain is Present: Looking at Two Sides
So what happens when someone has SI joint pain? Assuming they are cleared to exercise, it’s important to assess motor control, pelvic mobility, thoracic spine mobility and coordination, hip mobility, and foot function. On both sides of the body.
Phew. That sounds like a lot. And it is, but once you understand what you’re looking at, it becomes less intimidating.
Let’s take Meredith, for example. By the end of her first session, we identified three areas she needed to bring more awareness. The first was her rib position. She habitually held her ribs up, in an inspiratory position. This created a disconnect between her torso and her pelvis.
Try this:
Come into a standing position. Lift your ribs up high, like you are sticking your chest out. Walk a comfortable pace down the hall and back. Are your arms able to comfortably swing? Do you feel movement through your spine and pelvis?
Now, exhale, let your ribs soften down and back allowing your chest to be soft. Again, walk a comfortable pace down the hall and back. Does that feel different? What happens in your arms? What about in your spine.
The second thing Meredith needed to do was connect her entire right foot with the ground. She tended to roll to the outside of the right foot and not press her right big toe into the floor. Her normal standing position was with her right foot back and her right leg externally rotated. Bringing awareness into her right foot and big toe created a better platform on which her pelvis could rest. It also enabled Meredith to use more of the muscles in the right leg to deal with the force of ground, facilitating co-contraction throughout the lower extremity.
Try this:
Come into a standing position with your right foot slightly back of your left and turned out. Place most of your weight on the outside of your right foot (about seventy percent of the weight will be outside of your right foot and thirty percent will be on your left foot). What happens to your pelvis in this position?
Adjust your feet so they are more even and begin placing weight into your right big toe. How does your pelvis feel now?
The third thing Meredith needed to be aware of was the position of her right foot relative to her left foot and using her left foot more for support. Okay, that’s kind of two things, but they go hand in hand. Like many people with chronic injuries, Meredith was actually heavy on the side that was painful. The right side was bearing all of the load while the left leg felt light, as though it was disconnected from the ground. Creating more of a connection with the left side alleviated the right side from bearing the entire load.
Try this:
Come into a standing position like you did earlier with your right foot back and seventy percent of your weight on the outside of your right foot. Notice the position of the pelvis and what you notice in your legs.
Begin placing more of your weight in your left foot, allowing it to become more connected to the ground. As you do this, step your right foot forward so that it is slightly in front of your left foot and the right big toe is connected to the ground. Notice the position of your pelvis now. What do you feel in your legs? How do your feet feel against the ground?
A Quick Note about SI Joint Instability…
Obviously, there are many, many variations and things you can see when it comes to the SI joint pain and discomfort. This is just one example, but this blog post would explode into 4000 (or more) words if I began to dive into even a handful of other scenarios. However, it’s worth noting that sometimes people will feel like their SI joint isn’t stable.
When people use words like instability, it generally indicates that, for some reason, they don’t trust that specific part of their body to transfer load efficiently. There are a number of muscles that cross the hip joint, providing support to the SI joint. The gluteus maximus, specifically, may play an important role in generating compressive force at the SI joint and assist in transferring load from the lower extremity to the trunk (Added et al., 2018).
The thing about the gluteus maximus is it’s a large muscle, which means it requires large amounts of load to stimulate a change in strength.
What does this mean? Quite simply, that in order to feel more stable through the SI joint, 99.9%* of the time, the person needs to get stronger. One of the easiest ways to do this is to lift external loads during lower body dominant strength based tasks. Deadlifting, front squats, kettlebell squats, lunges, suitcase pick-ups…. Any combination of these movements (or similar movements) done progressively, in a thoughtful way, will increase strength, ultimately facilitating a sense of stability.
Conclusion:
In order for load to be transferred efficiently up (and down) the kinetic chain, both sides of the pelvis need to be able to rotate, both sides of the rib cage need to be able to rotate, the femurs need to be able to adequately rotate, and the feet need to be able to effectively handle the forces from the ground. This means there needs to be coordination between joints, independent joint mobility, and integrated strength throughout the body for each SI joint to efficiently disperse load. Remember that movement is a series of joint rotations and the two sides of the body don’t always share the brunt of the work equally. These two simple facts are often great hints for where to start.
*I totally made this statistic up; anecdotally, I have yet to see progressive strength training NOT create a sense of stability throughout the pelvic region.
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References:
Lewis C.L., Laudicina N.M., Khuu A., & Loverro K.L., (2017). The human pelvis: variation in structure and function during gait. Anatomy Records (Hoboken), 300(4), 633-642. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5545133/pdf/nihms887970.pdf
Rice J., Kaliszer M., Walsh, M., Jenkinson A., & O’Brien T., (2004). Movements at the low back during normal walking. Clinical Anatomy, 17(8), 662-666. https://doi.org/10.1002/ca.20003
Feipel V., De Medmaeker T., Klein P., & Rooze M., (2001). Three-dimensional kinematics of the lumbar spine during treadmill walking at different speeds. European Spine Journal, 10, 16-22. https://doi.org/10.1007/s005860000199
Vleeming A., Schuenke M.D., Masi A.T., Carreiro J.E., Danneels L., & Willard F.H., (2012). Journal of Anatomy, 221(6), 537-567. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3512279/
Added M.A.N., de Freitas D.G., Kasawara K.T., & Fukuda T.Y., (2018). Strengthening the gluteus maximus in subjects with sacroiliac dysfunction. International Journal of Sport Physical Therapy, 13(1), 114-120. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5808006/