SI Joint Fusion

Medically reviewed by Joshua L. Hare, DO, Founder & Medical Director

Conditions Treated

Chronic SI joint dysfunction refractory to injections and RF ablation, SI joint instability, sacroiliitis with joint degeneration

SI Joint Fusion at a Glance

How the Diagnosis Is Confirmed Before Fusion

Sacroiliac joint dysfunction is an important and underappreciated cause of chronic low back pain[1] — the joint sits at the junction of spine and pelvis, and pain from it is routinely mistaken for lumbar disc or hip trouble. That is why fusion comes last, after a deliberate sequence of confirmation. Before anyone discusses implants, the diagnosis has to be confirmed: image-guided diagnostic injections that reproduce and then abolish your pain, and usually a course of therapeutic injections and radiofrequency ablation first. Fusion enters the conversation only when the diagnosis is proven and the less invasive options have been used up. That selection discipline is why the trial results below look the way they do.

What Two Years of Trial Data Show

The INSITE trial randomized 148 subjects with SI joint dysfunction to minimally invasive fusion (102) or non-surgical management (46)[1] and followed them for two years.

The comparison arm matters as much as the headline: patients randomized to continue non-surgical care alone — the medications and therapy most people on this page have already tried — reached those improvement thresholds less than 10% of the time.[1]

What the Implants Actually Do

Through an incision of an inch or two in the buttock, guided by fluoroscopy, the surgeon passes rigid triangular titanium implants across the joint from the outer pelvis into the sacrum. Because the profile is triangular, the implants resist rotation as soon as they are seated, controlling the joint’s painful micromotion; over the following months, bone grows onto and across the implants, converting that mechanical stability into biological fusion. The weight-bearing restrictions in the first 4-6 weeks exist to protect exactly that process while it takes hold.

The Procedure, Step by Step

1. Anesthesia is administered at our ambulatory surgery center and you are positioned face down.
2. A small incision is made over the outer buttock.
3. Under fluoroscopic guidance, guide pins establish the trajectory across the SI joint.
4. The triangular implants — typically three — are placed across the joint and their position is confirmed on imaging.
5. The incision is closed; most patients go home the same day with a walker or crutches ready.
6. Weight-bearing advances gradually over 4-6 weeks, with full activity returning over 3-6 months as the fusion matures.

Risks and Side Effects

Every surgery carries risk — infection, bleeding, nerve irritation, anesthesia reactions — and this one adds the specific possibilities of implant malposition and, uncommonly, the need for revision. The trial put numbers on that: adverse events related to the fusion were infrequent, and 3 of 102 surgical patients required revision within two years.[1] Surgical soreness at the incision is expected for the first weeks, and the early weight-bearing limits mean you should plan for help at home. Your surgeon will review your individual risk profile with you — bone quality, medications, and health conditions all factor in.

Common Questions

How do I know my SI joint is really the problem?

By testing it directly. The diagnosis is confirmed with image-guided injections into the joint itself: if numbing the joint reliably switches your pain off, the source is established. Fusion is only discussed once that confirmation exists.

Why must injections and ablation come first?

Because many patients get durable relief from them and never need surgery at all. Fusion is permanent, so it is reserved for patients whose pain has come back after every less invasive option. The trial enrolled its patients through the same kind of screening.

How soon will I walk normally?

You will be up with support almost immediately, but weight-bearing through the fused side stays limited for 4-6 weeks. Most patients then progress steadily, with full, unrestricted activity typically returning over 3-6 months as bone locks the implants in.

Do the implants ever come out?

They are designed to stay for life — bone grows across them, which is the fusion. Revision is uncommon: three patients out of 102 needed one within the trial's two-year window.

References

Clinical sources for this page.

1. Polly DW, Swofford J, Whang PG, et al. Two-year outcomes from a randomized controlled trial of minimally invasive sacroiliac joint fusion vs. non-surgical management for sacroiliac joint dysfunction. International Journal of Spine Surgery. 2016;10:28. Back to first citation ↑