Sacroiliac (SI) Joint Injection in St. Louis

The sacroiliac joints are the two joints connecting the sacrum, at the base of the spine, to the iliac bones of the pelvis. They transfer the load of the upper body into the legs and move only a few millimeters. When inflamed or mechanically irritated they produce pain across the lower back, the buttock and sometimes the back of the thigh, a pattern easily mistaken for sciatica or a disc problem.

Under fluoroscopic guidance, contrast is used to confirm the needle has entered the joint before any medication is delivered. A local anesthetic and an anti-inflammatory steroid are then injected into the joint space. The procedure takes roughly fifteen minutes and is performed on an outpatient basis at our St. Louis office.

Because the anesthetic acts immediately, the injection doubles as a diagnostic test. Meaningful relief in the hours that follow confirms the SI joint as the pain generator; little or no change points the search elsewhere. That answer directs what comes next, whether repeat injection, radiofrequency treatment of the nerves supplying the joint, or a different diagnosis altogether.

Most patients return to light activity the same day. The anesthetic wears off within hours and the steroid effect typically builds over several days. We ask patients to record their pain levels across the first twenty-four hours, because that record is what makes the diagnostic part of the test meaningful.

The sacroiliac joint has an unusual innervation. Its posterior aspect receives contributions from the lateral branches of the S1 to S3 dorsal rami, and often from L5 and S4, and that supply varies considerably between individuals. There is no single nerve to test. Pain referred from the joint can appear in the buttock, the groin, the posterior thigh and occasionally below the knee, which is why it is so readily mistaken for a lumbar radiculopathy.

Imaging does not resolve it either. Degenerative change at the SI joint is common in asymptomatic adults, so a finding on CT or MRI does not establish that the joint is the source. No single physical examination maneuver is reliable on its own; the literature supports using a cluster of provocation tests, and even then the result raises or lowers suspicion rather than confirming it.

Because neither imaging nor examination is definitive, a controlled diagnostic block is what the field uses as its reference standard. The logic is simple: anesthetize the joint under fluoroscopic guidance with contrast confirming intra-articular spread, and see whether the pain goes. If it does, within the duration of the anesthetic, the joint is implicated. If it does not, it is not the source and continuing to treat it wastes time.

This is why we ask you to track your pain in the hours afterward, and why blind injection is not acceptable here. Without image guidance and contrast the needle frequently misses the joint capsule, and a missed injection produces a false negative that can send the entire workup in the wrong direction.