SI Joint Fusion
Minimally invasive stabilization of the sacroiliac joint for refractory SI joint pain
Sacroiliac (SI) joint fusion is a surgical procedure that permanently stabilizes the joint between the sacrum and the iliac bones of the pelvis. It is performed when SI joint dysfunction causes chronic low back, buttock, or leg pain that has not responded to conservative treatments including physical therapy and SI joint injections. Minimally invasive SI joint fusion techniques (such as the iFuse system) involve inserting small titanium implants across the SI joint through a lateral approach, with the procedure typically completed in under an hour.
Who Is a Candidate?
- Chronic SI joint pain confirmed by positive SI joint diagnostic injections (>75% pain relief)
- SI joint dysfunction unresponsive to at least 6 months of conservative care (physical therapy, bracing, injections)
- Sacroiliac joint instability following pelvic trauma or pregnancy-related ligament laxity
- Degenerative sacroiliitis confirmed on CT or MRI
- Failed prior conservative SI joint management in appropriate surgical candidates
What to Expect
1Before Surgery
Accurate diagnosis is critical — a positive response to a diagnostic SI joint injection (>75% pain relief for the duration of the anesthetic) is required before considering surgery. Pre-operative CT imaging maps the anatomy for implant placement. The procedure is performed under general or spinal anesthesia and typically takes 30–60 minutes.
2The Procedure
For minimally invasive SI joint fusion, a small incision (1–2 cm) is made on the side of the buttock. Under fluoroscopic X-ray guidance, 2–3 titanium triangular implants are inserted across the SI joint from the ileum into the sacrum. The implants are designed to allow bone ingrowth, leading to permanent fusion of the SI joint. There is no suturing of the joint itself — the implants mechanically stabilize the joint and the bone fuses over time.
3Recovery
Most patients go home the same day or after one night. Weight-bearing with a cane or walker is allowed immediately, but full weight-bearing is typically permitted within 2–4 weeks. Return to desk work in 2–4 weeks; physical labor in 3–6 months. Physical therapy begins at 4–6 weeks focusing on gait and hip strengthening. Most patients experience progressive pain reduction over 3–6 months as fusion consolidates.
Typical Outcomes
SI joint fusion has demonstrated consistent effectiveness in well-selected patients. Randomized controlled trials show approximately 80% of patients achieve >50% pain reduction at 2 years compared to less than 30% with continued conservative care. Long-term data at 5 years shows maintained benefit for most patients. The key to success is accurate pre-operative diagnosis — patients who respond poorly to diagnostic SI joint injections are unlikely to benefit from surgery.
Risks & Considerations
- Implant malposition — risk reduced with fluoroscopic guidance but carries nerve proximity risk
- Adjacent joint degeneration — the hip and lumbar spine may bear more stress after SI fusion
- Non-fusion (failure of bone ingrowth) — more common with poor bone density
- Wound infection
- Nerve injury (L5 nerve root is proximate to the implant trajectory)
- Failure to achieve pain relief if the SI joint was not the primary pain generator
Frequently Asked Questions
How is minimally invasive SI joint fusion different from open SI joint fusion?
Traditional open SI joint fusion requires a larger incision, more tissue dissection, and longer recovery. Minimally invasive techniques (lateral approach with triangular titanium implants, such as the iFuse procedure) use a 1–2 cm incision, have significantly faster recovery, and have strong Level I clinical evidence supporting their effectiveness.
How do I know if my pain is coming from the SI joint?
SI joint pain is notoriously difficult to diagnose clinically. Symptoms include low back pain, buttock pain, and sometimes groin or posterior thigh pain. The gold standard for diagnosis is a fluoroscopy-guided SI joint injection — if you get >75% relief for the duration of the anesthetic, the SI joint is confirmed as a pain generator. This is required before surgical intervention.
Can SI joint pain come back after fusion?
Once solid fusion is confirmed, the SI joint itself should not cause pain. However, patients may develop adjacent joint pain (the hip or the lumbar spine) over time as those structures absorb the forces the SI joint once distributed. This is why SI joint fusion is reserved for patients who have definitively failed all conservative options.
What is the recovery like compared to lumbar fusion?
SI joint fusion recovery is generally faster than lumbar spinal fusion. Most patients are weight-bearing the same day, return to light activity in 2–4 weeks, and experience meaningful pain reduction within 1–3 months. Lumbar fusion typically has a longer recovery with more post-operative restrictions. However, SI joint fusion recovery varies by individual and depends on pre-operative deconditioning.
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Medical disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions you may have regarding a medical condition or surgical procedure. Last reviewed March 2026. CPT: 27279.