The sacroiliac (SI) joint gets blamed for a lot of pain it probably isn’t causing. It’s not that clinicians are acting in bad faith. It’s that once you’re trained to look for something, confirmation bias makes it easy to keep finding it, even when the evidence says it’s uncommon.
A Joint Built Not to Move
The SI joint connects the pelvis (the innominate bones) to the sacrum, and unlike most joints in the body, its job isn’t mobility. It’s stability. Dense bone contact, strong ligament support, and large surrounding muscles all work to keep this joint from moving much at all. Precise imaging studies using stereophotogrammetry have measured just a few degrees of rotation and a fraction of a millimeter of translation under real loading, and that already-small range shrinks further with age: cartilage surfaces gradually turn to bony ridges after the third decade, stiffening the joint further by the time most people reach their 50s and 70s.
That combination, a joint engineered for stability that gets stiffer with age, makes it an inherently unlikely source of ongoing pain, and an even less likely explanation for pain showing up somewhere else entirely, like the hip or lumbar spine.
Why It Gets Blamed Anyway
Low back pain is close to universal. More than 90% of people will experience it at some point, and the large majority of cases are benign and resolve quickly with physical therapy, as we’ve covered elsewhere. Within the smaller population of people with chronic low back pain, only around 13% respond to a diagnostic SI joint injection, which is the closest thing this field has to a reference standard for confirming the joint as the actual pain generator.
That’s a real number, but a small one. A clinician who’s primed to see SI dysfunction everywhere will often find it far more often than that 13% would predict, not because the joint changed, but because the search did.
Why the Old Diagnostic Approach Falls Apart
Early SI examination relied on locating bony landmarks on the pelvis and comparing their position side to side. That approach has real problems: patient tissue can make landmarks hard to palpate precisely in the first place, and asymmetry between landmarks is the norm anatomically, not the exception. A landmark that looks “high” or “rotated” on one side might just be a naturally different size. For more on exactly how unreliable these tests are in practice, see our review of SI joint testing.
Movement-based tests haven’t fared much better. Studies have found abnormal or asymmetric SI movement in people with no symptoms at all, and inconsistently on the involved versus uninvolved side in people who do have symptoms, driving high false-positive and false-negative rates. More recent research suggests a lot of that asymmetry actually reflects weakness or coordination deficits rather than a true difference in joint mobility, which is part of why core and hip strengthening plays a role in treatment even when the SI joint itself isn’t the primary problem.
Given how unreliable any single test is, the better-supported approach is a cluster of three to four provocation tests rather than one static or motion-based test in isolation, and ruling out the lumbar spine first, since it’s a far more likely source of low back pain to begin with.
What This Means for Treatment
None of this means the SI joint can never be the problem. It means it’s overdiagnosed relative to how often it’s genuinely the source. Once it’s identified accurately, through a proper cluster exam rather than landmark palpation, manual therapy and exercise are well-supported treatments. We cover what that evidence actually shows in what the evidence says about PT for SI joint pain, and why manipulation still helps even though it isn’t repositioning anything, in SI joint manipulation works, just not how you think.
If you’ve been told your pain is coming from a misaligned or unstable SI joint and treatment hasn’t helped, it’s worth an evaluation that actually rules the lumbar spine and hip in or out first. Book an SI joint evaluation at Mend’s Boulder or Lafayette clinic.
Browse more of our sacroiliac joint pain coverage, or see the full Orthopedic Care library.
