Who is a candidate?
SI joint fusion is considered only at the end of a deliberate sequence: pain localized to the joint, reproduced on examination, relieved by a diagnostic injection, and persisting despite an adequate course of physical therapy, activity modification, and therapeutic injection. Patients who have had a previous lumbar fusion are over-represented, because that alters how load passes through the pelvis.
How the procedure works
Through a small incision on the side of the buttock, and guided by X-ray, implants are passed across the joint from the outer pelvis into the sacrum. They provide immediate stability and a surface for bone to grow across, fusing the joint over the following months. The operation is typically short, and the muscle is spread rather than cut.
Recovery
Most people go home the same day or the next. Weight-bearing is usually protected with crutches or a walker for a period while the implants integrate, after which walking is progressed. Physical therapy resumes once the early healing phase is complete. Bone growth across the joint continues over several months.
Benefits and alternatives
For carefully selected patients the intended benefit is durable relief of a pain source that has already proven responsive to blocking the joint. Alternatives are continued physical therapy targeted at the pelvis and hips, a supportive belt, repeat therapeutic injections, and radiofrequency treatment of the nerves supplying the joint.
Risks
Risks include infection, bleeding, nerve irritation or injury, the nerve roots exiting the sacrum run close to the implant path, implant malposition, failure of the joint to fuse, and continued pain if the joint was not in fact the source. That last risk is precisely why the diagnostic workup carries so much weight.