Sacroiliac (SI) Joint Dysfunction
What it is
The sacroiliac joints sit where the base of your spine (the sacrum) meets your pelvis, one on each side. They carry a lot of load and normally move very little. When one becomes irritated or starts moving abnormally, it can produce pain — a common and often under-recognized source of low back and buttock pain that can closely mimic a pinched nerve.
What it feels like
The pain is usually on one side, low and toward the buttock, sometimes spreading into the groin or the back of the thigh — but it typically does not travel below the knee. People often notice it most with transitions: rising from a chair, climbing stairs, rolling over in bed, or standing on one leg to get dressed.
How we diagnose it
I use specific exam maneuvers that load the joint to see whether they reproduce your familiar pain. Imaging often looks normal, which does not rule the joint out. The most reliable test is a numbing injection into the joint under X-ray guidance: if it clearly relieves your pain, the joint is very likely the source.
How we treat it
Most people improve without surgery:
- Physical therapy focused on core and pelvic stability
- Anti-inflammatory medication when appropriate
- A steroid injection into the joint, which can both confirm the diagnosis and relieve pain
- Radiofrequency ablation (quieting the small nerves to the joint) if relief from injections is short-lived
For the smaller number of people whose pain keeps returning despite these steps, a minimally invasive SI joint fusion can be an option. We would get there only after the simpler measures, and after the numbing injection has confirmed the joint is truly the source.
The science — for the curious
Because SI joint pain can spread into the leg, it is frequently mistaken for a disc or sciatica problem — and the treatments for those are completely different. That is exactly why the diagnostic injection is so valuable: confirming whether the pain truly comes from the joint keeps us from treating the wrong thing. Getting the source right is most of the work.
Learn more
OrthoInfo — Spinal Injections: orthoinfo.org
OrthoInfo — Low Back Pain: orthoinfo.aaos.org
This handout is general education about a common condition and does not replace the personalized advice we discuss in clinic. If anything here does not match what we talked about, what we talked about wins — please ask me.