Sacroiliac (SI) Joint Dysfunction

The sacroiliac (SI) joints connect your spine to your pelvis. When one of them becomes inflamed or moves abnormally, it can cause low back and buttock pain that is easy to mistake for a disc problem. SI joint pain accounts for an estimated 15–30% of chronic low back pain.

What's happening in your spine

Your sacrum (the triangular bone at the base of your spine) meets each side of your pelvis at the SI joints. These joints move only a few millimeters but absorb enormous load every time you walk, climb stairs, or get up from a chair. Pregnancy, trauma, leg-length differences, prior lumbar fusion, and arthritis can all upset the way these joints carry load and cause pain.

Common symptoms

• Pain in the lower back, buttock, or back of the upper thigh
• Pain on one side that worsens with prolonged sitting, standing, or stair climbing
• Sharp pain when you stand from a seated position
• A feeling of instability or 'giving way' in the low back or pelvis
• Pain that radiates into the groin but rarely below the knee

Causes & risk factors

Common contributors include pregnancy and postpartum pelvic changes, falls onto the buttock, repetitive heavy lifting, arthritis of the joint, prior lumbar spine fusion (which transfers extra load to the SI joint), and inflammatory conditions such as ankylosing spondylitis.

How it's diagnosed

Diagnosis is built from your history, an exam with specific provocation tests of the SI joint, and imaging to rule out other causes. The most accurate confirmation is a diagnostic image-guided injection of numbing medicine into the joint — if it relieves your typical pain, the SI joint is the source.

Treatment options

Most patients improve with a stepwise non-surgical program.

• Physical therapy targeting the core, hips, and pelvic stabilizers
• Anti-inflammatory medication and activity modification
• SI belt for short-term support, especially in pregnancy-related pain
• Image-guided SI joint steroid injections
• Radiofrequency ablation of the nerves supplying the joint for confirmed, recurrent SI joint pain

When non-surgical care and injections fail and the SI joint has been clearly confirmed as the pain source, a minimally invasive SI joint fusion may be considered. This is a small procedure that stabilizes the joint with implants placed through a tiny incision.

When to see a specialist

See a specialist if buttock or low back pain has not improved after 6–8 weeks of non-surgical care, if pain is interfering with walking or sleep, or if it returns after each round of treatment.