What's the Difference Between Sacroiliac (SI) Joint Pain and Regular Lower Back Pain?

Sacroiliac, or SI, joint pain and typical lower back pain come from different structures and often feel different. SI joint pain is usually felt lower and off to one side, near the dimples above your buttock, while lumbar facet or disc-related pain tends to sit more centrally at belt level. The SI joint is also responsible for an estimated one in four cases of chronic low back pain, yet it's rarely the primary focus of a standard back pain evaluation.

If you've been treated repeatedly for "lower back pain" in general and never gotten lasting relief, there's a real chance the joint actually involved has never specifically been assessed.

A Different Joint, and a Reason It Gets Overlooked

The sacroiliac joint sits where your sacrum, the triangular bone at the base of your spine, meets your ilium, the wing-shaped bone of your pelvis. Under normal circumstances it has very little motion, just a few degrees, but it's densely innervated and can be a genuine and significant source of pain when irritated. Its referral pattern is fairly characteristic: pain concentrated low and to one side, often near the small dimples above your buttock, that can extend into the buttock, groin, or upper thigh, but rarely travels past the knee the way true nerve root pain often does. This is a meaningfully different pattern than the more central, midline discomfort typical of lumbar facet or disc-related pain.

The second reason this joint gets missed so often connects directly to the rest of this cluster. When the lumbar spine above the SI joint is restricted, from the same facet joint stiffness and multifidus inhibition covered throughout this series, the SI joint, which is built for very limited motion to begin with, can be forced to compensate by moving more than it's designed to. That extra demand leads to irritation and instability at a joint with minimal reserve capacity for it. On top of that, standard lumbar MRI protocols are built around the discs and vertebrae, not the SI joint specifically, so a completely normal-looking lumbar scan doesn't rule out a genuinely painful SI joint sitting just below the area the imaging was focused on.

When It's Something More Serious

Most SI joint pain is mechanical and responds well to targeted treatment. Get evaluated promptly, however, if the pain follows significant trauma like a fall directly onto your buttock or a car accident, or if it's accompanied by fever, since joint infection, while uncommon, requires prompt medical attention.

How This Gets Addressed

Because the SI joint responds to different treatment techniques than the lumbar spine above it, resolving this well starts with correctly identifying that the SI joint is actually involved.

Chiropractic care uses SI joint-specific mobilization and adjustment techniques directly addressing the joint movement itself.

Massage therapy releases the compensating tension in the glute and piriformis muscles that build up around an irritated SI joint, and dry needling reaches that same muscle group with more precision when the tension has become chronic.

Physical therapy addresses this from two directions at once: SI joint-specific stabilization exercises, which are meaningfully different from general core work and target the joint's limited natural stability directly, along with continued lumbar mobility work to reduce how much the SI joint has to compensate for restriction above it.

And because hormonal factors, particularly during and after pregnancy, and general systemic inflammation can both affect SI joint stability and sensitivity, naturopathic medicine evaluates these contributors through targeted lab testing when relevant.

You can learn more about our full approach to low back pain here.

Most patients whose pain has been treated as generic lower back pain without improvement notice a real difference once the SI joint is specifically identified and addressed as its own structure.

Written By:

Dr. Jason Winkelmann

Naturopathic doctor, Chiropractor, Chronic Pain Specialist, and Educator

Frequently Asked Questions

How is SI joint pain diagnosed if it doesn't show up well on standard imaging? 

SI joint involvement is primarily identified through a physical examination using specific provocative tests that stress the joint directly, rather than through imaging alone. This is part of why it's frequently missed in evaluations that rely mainly on an MRI focused on the lumbar spine.

Can SI joint pain happen on both sides at once? 

It can, though it's more commonly one-sided, especially when it's related to a compensation pattern from lumbar restriction above. Bilateral SI joint pain is more often associated with inflammatory or hormonal contributors and is worth a more thorough evaluation.

Is SI joint pain more common after pregnancy? 

Yes. Hormonal changes during pregnancy increase ligament laxity throughout the pelvis, including at the SI joint, which can make it more prone to irritation and instability both during and after pregnancy.