SI Joint Fusion in St. Louis

The sacroiliac joints sit where the base of the spine meets the pelvis, one on each side. They move very little, and they are built to transfer load rather than to provide range of motion. When one becomes a pain generator, the standard tools of spine care often miss it entirely, because it is not the spine.

Minimally invasive SI joint fusion stabilizes that joint. Through a small incision at the side of the buttock, under live X-ray guidance, implants are placed across the joint to stop the painful micro-motion and allow bone to grow across it. It is a surgical procedure, performed in a single outpatient session.

This is distinct from the sacroiliac joint injection, which is both a diagnostic and a therapeutic tool. The injection tells you whether the joint is the source. Fusion is what you consider when the answer is yes and the relief from injection does not hold.

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The sacroiliac joint is a recognized source of pain in a substantial minority of people with low back pain. Published estimates range from about 10 to 30 percent, and the spread is not sloppiness — it reflects how the diagnosis was made. Studies requiring two confirmatory blocks report different figures from those accepting one, which is the same point made in the diagnosis section below. Either way it is a large share of a very large population, and it is routinely overlooked.

The reason is partly anatomical. SI joint pain sits low and to one side, often over the back of the pelvis, and radiates into the buttock, groin or back of the thigh. It is easily read as a disc problem or as sciatica. Lumbar imaging looks at the lumbar spine, and a joint that is not in the picture cannot be found in it.

Two patterns should raise the question directly: pain that has persisted after a lumbar fusion — where load transfers to the joint below — and pain that began during or after pregnancy, when ligamentous laxity changed how the pelvis handles load.

The diagnosis is not made on imaging alone, because degenerative changes at the SI joint are common in people with no pain at all. It is made by combining examination with a diagnostic block.

Provocative physical examination maneuvers stress the joint in specific directions. Where several are positive together, suspicion rises. Confirmation comes from an image-guided injection of local anesthetic into the joint: if the pain reliably falls while the anesthetic is working and returns as it wears off, the joint has identified itself.

This step is not optional and it is not a formality. Every major trial of SI joint fusion required diagnostic block confirmation before enrolling a patient, and coverage policy generally requires it as well. A fusion performed on a joint that was never proven to be the pain generator is a procedure with no reason to work.

The evidence here is stronger than for many interventional procedures, and it comes from randomized trials rather than case series.

A 2015 multicenter randomized controlled trial in Neurosurgery assigned 148 patients with SI joint dysfunction to either minimally invasive fusion with triangular titanium implants or non-surgical management. At six months, success rates were 81.4 percent in the surgical group against 26.1 percent with non-surgical care. Clinically important improvement in the Oswestry Disability Index — a fall of at least 15 points — occurred in 73.3 percent of the fusion group against 13.6 percent of the non-surgical group. Improvements were sustained at twelve months, and patients who crossed over from non-surgical to surgical care improved similarly.

A 2016 European randomized trial in the European Spine Journal compared fusion against conservative management across nine sites in four countries. At six months, low back pain improved by 43.3 points in the fusion group against 5.7 with conservative care. Disability scores improved by 26 points against 6. Adverse event rates did not differ between the groups.

Both of the trials above compared fusion against non-surgical care. Neither compared it against a sham operation, and that distinction matters more in surgery than in most fields, because the placebo response to an operation is substantial and well documented.

Researchers in Norway and Sweden thought it mattered enough to run a double-blind, sham-controlled trial specifically to find out, writing plainly that it remains unclear how much of the observed benefit reflects the placebo effect. That trial exists because the question is open, not because the procedure is doubted.

It is also worth knowing that the major fusion trials were industry-sponsored, with implant manufacturer involvement in authorship. That does not make the results wrong — they are randomized, multicenter and published in peer-reviewed journals — but you are entitled to know it when weighing them.

What follows from all of this is not skepticism about the procedure. It is that patient selection carries most of the weight. The trials enrolled patients whose SI joint had been confirmed as the pain source and whose conservative care had failed. Outcomes in that population say little about outcomes in a patient who has not been through the same filter.

We implant SI-BONE devices, and which one is used depends on your anatomy and on the surgical approach that fits it.

The iFuse Implant System uses triangular titanium implants placed laterally across the joint. Its triangular profile resists rotation, and its porous surface is designed for bone to grow onto and into. This is the implant used in both randomized trials described above, which means the published outcomes and the device are directly linked rather than extrapolated.

The Catamaran SI Joint Fusion System uses a different trajectory across the joint, designed to place a single larger implant along the axis of the joint rather than several across it. It suits certain pelvic anatomies better than a lateral approach does.

Both are manufactured by SI-BONE, Inc. and cleared for this use. Neither is a brand we are affiliated with commercially — they are the instruments, and the choice between them is a surgical judgment about your pelvis, not a preference.

SI joint fusion is performed as an outpatient procedure under local anesthetic with mild sedation. An IV is placed, a light sedative given, and the surgical site numbed. The implants are placed under live X-ray guidance through a small lateral incision. Most patients go home the same day.

Because mild sedation is used, arrange for someone to drive you home.

Keep the site clean and dry, and plan on a follow-up visit in the clinic within five to ten days so the result can be assessed directly. Do not lift anything over 20 pounds for two weeks.

Most patients are walking the same day, with weight-bearing guided by comfort rather than by a fixed schedule. Pain in the first several days after the procedure is common and expected — it reflects the surgical work rather than a failure of it.

There is no national Medicare coverage determination for SI joint fusion. Coverage is set regionally: in Missouri the Medicare contractor publishes a local coverage determination covering percutaneous minimally invasive fusion of the sacroiliac joint, with specific criteria attached. Commercial policies vary and are checked individually.

Those criteria are consistent in what they ask for, and they align with good practice regardless of who is paying: a documented period of failed conservative care, examination findings pointing at the joint, and confirmation by diagnostic block. This is one of the cases where the payer’s requirements and the clinical requirements point the same direction.

We do not publish prices, because what a given patient needs is established at evaluation. Call (314) 481-5000 and we will check your specific coverage and tell you where you stand before anything is scheduled.

Fusion is not an early step. It is what remains when the joint has been identified, conservative care has genuinely been tried, and the relief from injection is real but temporary.

Before it: activity modification and targeted physical therapy aimed at the pelvis rather than the lumbar spine, and SI joint injection for both diagnosis and treatment. For some patients, radiofrequency ablation of the nerves supplying the joint gives durable relief without fusing anything.

Dr. Gurpreet Singh Padda, MD, MBA, MHP is a licensed physician and surgeon with surgical privileges, and this practice performs SI joint fusion. It leads with the least invasive option that can answer the question, and reserves fusion for when the joint has proven itself the source and nothing short of stabilizing it has held.