Dr. Zeeshan Sardar, MD, MSc, F.R.C.S.C
Director, Quality & Patient Safety (QPS) – Och Spine Hospital
Medical Director, Spine Unit – Och Spine Hospital
Co-Chief of Spinal Deformity Surgery • NewYork-Presbyterian / Columbia University
Och Spine Hospital • New York, NY
Sacroiliac joint (SIJ) dysfunction is one of the most common and most frequently misdiagnosed causes of lower back and buttock pain. It accounts for an estimated 15–30% of cases of chronic lower back pain — yet it is frequently attributed to lumbar disc disease, facet arthritis, or sciatica without the sacroiliac joint being appropriately evaluated. Understanding the SI joint and its role in spine-related pain is important for patients who have had persistent symptoms despite treatment directed at the lumbar spine.
WHAT IS THE SACROILIAC JOINT?
The sacroiliac joint connects the sacrum (the triangular bone at the base of the spine) to the ilium (the large pelvic bone) on each side. There are two SIJ — one on each side of the pelvis. The joints are relatively stiff and allow only a few degrees of motion, but they bear significant mechanical load and are subject to the same degenerative and inflammatory processes that affect other joints. Pain from the SI joint is typically felt in the lower back, buttock, and posterior thigh — a distribution that overlaps significantly with lumbar disc disease and sciatica, making accurate diagnosis challenging without targeted evaluation.
CAUSES
- Degenerative sacroiliitis — age-related degeneration of the joint surface
- Prior lumbar fusion extending to the sacrum — places increased mechanical stress on the joint and is a well-recognized cause of secondary SIJ pain
- Inflammatory arthritis — ankylosing spondylitis and seronegative spondyloarthropathies frequently involve the SIJ
- Pregnancy-related ligamentous laxity — hormonal changes relax the SIJ ligaments, producing instability and pain that may persist postpartum
- Trauma — falls onto one side or motor vehicle accidents can injure the SIJ
SYMPTOMS
- Lower back and buttock pain, typically one-sided, located just medial to the posterior superior iliac spine
- Pain with prolonged sitting, standing, or transitional movements (getting up from a chair)
- Pain with activities that load one side of the pelvis (climbing stairs, walking on uneven ground)
- Radiation into the posterior thigh, rarely below the knee
- No neurological symptoms — this helps distinguish SIJ pain from lumbar radiculopathy, though the two can coexist
DIAGNOSIS
SIJ dysfunction is primarily a clinical and procedural diagnosis. MRI and CT can identify inflammatory changes or degeneration but are often normal in patients with symptomatic SIJ dysfunction. Provocative physical examination tests (FABER test, thigh thrust, distraction and compression tests) can suggest SIJ involvement. The most reliable diagnostic test is a fluoroscopically guided diagnostic injection of local anesthetic into the joint — significant pain relief (typically ≥50–75% reduction) following the injection confirms the SIJ as a significant pain generator.
TREATMENT
Non-surgical treatment is first-line: SIJ-specific physical therapy targeting the gluteal, hip abductor, and core musculature; activity modification avoiding asymmetric loading; SI belt for support during activity; and fluoroscopically guided corticosteroid injections into the joint for weeks to months of relief. For patients with significant, disabling SIJ pain that has failed conservative measures including repeated injections, minimally invasive SIJ fusion — stabilization of the joint using small titanium implants inserted percutaneously — is an option with a growing evidence base. Dr. Sardar evaluates each patient individually and refers to specialists with specific expertise in SI joint fusion when this option is indicated.
A NOTE FOR PATIENTS AFTER LUMBAR FUSION
Patients who have undergone lumbar spinal fusion — particularly long fusions that cross the lumbosacral junction — are at significantly elevated risk of developing SIJ dysfunction after surgery. The SI joint must absorb increased mechanical load when the lumbar spine above it is fused. Any patient with persistent or new lower back and buttock pain after lumbar fusion should be specifically evaluated for SIJ involvement.
FREQUENTLY ASKED QUESTIONS
Why was my SI joint pain mistaken for a disc problem?
SI joint pain often overlaps in location with lumbar disc and sciatic pain, and imaging frequently appears normal even when the joint is the actual source, making it easy to overlook without targeted testing.
How is SI joint dysfunction actually confirmed?
The most reliable test is a fluoroscopically guided diagnostic injection. Significant pain relief after the injection confirms the joint as a true source of pain.
Can SI joint dysfunction happen after a fusion that didn’t even involve the SI joint?
Yes. Lumbar fusion increases mechanical stress on the SI joint below it, making new SI joint pain a recognized possibility after lumbar fusion surgery.
Will physical therapy actually help?
Yes, SIJ-specific physical therapy targeting the surrounding hip and core muscles is the first-line treatment and helps many patients significantly.
When is SI joint fusion considered?
Only after conservative treatment, including repeated injections, has failed to provide adequate relief for significant, disabling pain confirmed to originate from the joint.
This page is for educational purposes only and does not constitute individualized medical advice.
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