Sacroiliac joint fusion stabilizes a joint that has been proven — not assumed — to be the source of the pain.
It sits at the end of a sequence, not the start
The sacroiliac joint causes a large share of chronic low back pain. It is the most often missed source, because it looks normal on MRI even when it is causing all of the pain.
Fusion is the last step in a set order. Skipping any part of it is how this procedure ends up done on the wrong patient:
- Clinical examination using a group of provocation tests (hands-on tests that try to bring on the pain). No single test is reliable on its own.
- Image-guided diagnostic injection, with contrast dye confirming the medicine is truly inside the joint. A landmark-guided injection (placed by feel, without imaging) that missed proves nothing.
- Repeat confirmation, because a single positive block can give a false positive.
- Conservative treatment — physical therapy, therapeutic injection, and radiofrequency ablation of the lateral branches (the small nerves that carry pain from the joint) where it fits.
- Fusion, only when the joint is confirmed and the relief from the steps above was real but short-lived.
PRP and the other orthobiologics we use for the low back and pelvis are explained on our PRP injections in St. Louis page.
Who is a candidate for SI joint fusion?
- Confirmed sacroiliac joint pain, established by image-guided diagnostic block
- Pain lasting beyond six months despite proper conservative treatment (care without surgery)
- Good but temporary relief from injections or lateral branch ablation
- Often, patients with pain after a lumbar fusion, where load has shifted to the joint below
- Post-traumatic sacroiliac injury that has not settled
How is SI joint fusion done?
It is done through a small incision (opening) at the side of the buttock under fluoroscopic guidance (live X-ray). Implants are placed across the joint to hold it steady and let the two bone surfaces fuse. There are several implant systems. The choice depends on your anatomy and the shape of the joint.
It is a day procedure in most cases. Weight-bearing is restricted for a period afterwards while the fusion consolidates, and physical therapy follows.
Why the diagnostic sequence matters so much here
Fusion cannot be undone. A fused sacroiliac joint stays fused. If the joint was not the pain source, the pain does not go away, but the joint is still fused.
That is the whole case for the confirming blocks. They are not paperwork hoops. They are what separates a patient who will do well from one who will have had a permanent procedure for nothing.
What is recovery like after SI joint fusion?
- Restricted weight-bearing on that side for a defined period, with crutches or a walker initially.
- Physical therapy once the early restrictions lift.
- Improvement over months rather than days, as the fusion consolidates.
- A driver and someone to help at home for the first days.
What is the downside of SI joint fusion?
This is a surgical procedure rather than an injection, and the risks reflect that. They include bleeding, infection, and nerve irritation from where an implant sits. An implant can loosen or sit in the wrong spot. And pain can continue if the joint was not the true source. Recovery involves a period of protected weight bearing. The sacroiliac joint sits close to the L5 and S1 nerve roots, so short-lived nerve irritation afterward is not unusual.
To find out whether this applies to you, call or text us. We are at 12174 Natural Bridge Rd, Suite 110, St. Louis, MO 63044.
How we judge whether it worked
It sits at the end of a diagnostic sequence, never at the start. To confirm the joint, we need repeated image-guided intra-articular blocks (injections inside the joint) that give strong relief every time. One positive injection is not enough. Imaging findings are not enough.
The reason for that care is simple. Fusing a joint that was not causing the pain leaves the patient with the original pain plus a fused joint. Getting the diagnosis right is the whole safeguard.
Before and after your procedure
This is surgery, so there is more to prepare. You will get specific instructions on medicines, fasting and weight bearing after surgery. Arrange help at home for the first week or two. Expect a period of limited activity while the fusion firms up. Expect the rehab afterward to matter as much as the procedure.
Common questions
Will I lose movement in that joint?
The sacroiliac joint has very little movement to begin with, just a few degrees. Fusing it does not cause the loss of motion people expect from fusing a joint with a wide range of motion.
There is more on this in Sacroiliac Joint Pain.
Why did my pain start after a lumbar fusion?
A fused lumbar segment does not move, so load shifts to the joints below it. New one-sided low back pain after a fusion comes from the sacroiliac joint far more often than from a failure of the fusion.
Ablation of the joint’s nerves, the step before fusion, is described in Sacroiliac Joint Radiofrequency Ablation.
Can I have this without the diagnostic injections?
No, and we refuse to do it. The injections are what show that the joint is the source, and the procedure cannot be undone.
The diagnostic injection is described in Sacroiliac Joint Injection.
Is this major surgery?
It is minimally invasive and usually a day procedure. But it is still a fusion with a real recovery. It is not comparable to an injection.
What if the blocks are negative?
Then the joint is not your pain source, and fusing it would do nothing. That is a useful result. It points the search somewhere else.
Can you walk normally after SI joint fusion?
Not right away. Weight-bearing on the treated side is restricted for a defined period while the fusion consolidates, so you start on crutches or a walker. Physical therapy begins once those early restrictions lift, and improvement comes over months rather than days. Arrange a driver and someone to help at home for the first week or two.
Can SI joint fusion be undone?
No. A fused sacroiliac joint stays fused. That is why we fuse only a joint that repeated image-guided blocks have confirmed as the pain source. And only after therapy, injections and nerve ablation gave real but short-lived relief. If the joint was not the source, the pain stays and the joint is still fused. So the diagnosis comes first.
Sources
- Yson SC et al. Sacroiliac Joint Fusion: Approaches and Recent Outcomes. PM & R : the journal of injury, function, and rehabilitation, 2019. PubMed 31169362
- Mehkri Y et al. Outcomes After Minimally Invasive Sacroiliac Joint Fusion: A Scoping Review. World neurosurgery, 2022. PubMed 36174944
- Rainov NG et al. Triangular titanium implants for sacroiliac joint fusion. Acta neurochirurgica, 2024. PubMed 39557713
- Wessell JE et al. Sacroiliac Joint Fusion-A Shift Toward Variant Anatomy and Clinical Implications. World neurosurgery, 2022. PubMed 36202341
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