Sacroiliac Joint Injection

Overview

A sacroiliac (SI) joint injection places a small amount of medication directly into or around the joint where the base of the spine meets the pelvis. It is one of the few spine-related procedures that does double duty: it can act as a diagnostic test to confirm the SI joint is truly the source of your pain, and it can act as a treatment by calming inflammation inside the joint. Because the SI joint sits so close to the lower lumbar spine and refers pain into similar areas, this injection is often the deciding step that separates an SI joint problem from a disc or nerve problem.

The procedure itself is brief, typically performed in an outpatient clinic or radiology suite, and uses image guidance to make sure the needle reaches the joint accurately rather than nearby nerves, blood vessels, or the pelvis.

When it's recommended

An SI joint injection is usually considered after a course of conservative care, such as activity modification, physical therapy, and anti-inflammatory medication, has not fully resolved one-sided low back, buttock, or groin pain, especially when a cluster of physical exam maneuvers suggests the SI joint rather than the lumbar spine. It is also used earlier in the workup when the diagnosis is unclear and a physician wants an objective answer before recommending further treatment, since imaging alone (MRI or CT) often cannot reliably confirm the SI joint as a pain generator on its own.

The injection is considered diagnostic when only local anesthetic is used and the goal is to see whether numbing the joint reproduces relief of your typical pain. It is considered therapeutic when a corticosteroid is added to reduce inflammation for longer-lasting relief, or when it is repeated after an initial diagnostic response. Many patients receive a combined injection that serves both purposes in a single visit.

How it works

You will lie face down on an imaging table. After the skin is cleaned and numbed, the physician uses fluoroscopy (a live, low-dose X-ray) or ultrasound to guide a thin needle into the SI joint capsule. Contrast dye is often injected first under fluoroscopy to confirm the needle tip is truly inside the joint before any medication is given, since the joint space is narrow and irregularly shaped. Ultrasound guidance is a radiation-free alternative that research shows can achieve comparable accuracy in experienced hands, sometimes paired with fluoroscopic confirmation. Injecting without any imaging guidance, using landmarks alone, is not recommended because of the risk of missing the joint or injecting near a lumbar nerve root, the sacral foramina, or the pelvis.

Once the needle position is confirmed, the physician injects a mixture of local anesthetic, a corticosteroid, or both. The whole procedure usually takes 15 to 30 minutes.

Preparing for the procedure

Before the injection, tell your physician about any blood thinners, aspirin, or supplements you take, since some may need to be paused beforehand per their instructions, as well as any allergies to contrast dye, local anesthetics, or steroids. Most patients do not need general anesthesia, so fasting requirements are minimal or none, though your clinic will give specific instructions. Because you may be asked to walk, climb stairs, or otherwise try to reproduce your usual pain shortly after the injection to test its diagnostic value, wear comfortable clothing and, if possible, arrange a ride home in case of temporary soreness or lightheadedness.

Recovery and aftercare

Most patients go home the same day. You may notice significant, temporary relief within the first hour or two while the local anesthetic is active; this window is when your physician will ask you to test your usual pain-provoking movements to gauge how well the injection worked. Mild soreness at the injection site for a day or two is common and typically responds to ice and over-the-counter pain relievers. If a steroid was included, its anti-inflammatory effect builds over the following days and may last weeks to months. Many clinics recommend limiting strenuous activity for 24 to 48 hours and easing back into normal activity, including physical therapy, as tolerated.

Risks and considerations

Sacroiliac joint injections are generally safe when performed with image guidance. Possible risks include temporary soreness or bruising at the injection site, infection, bleeding, a vasovagal (fainting) reaction, transient leg numbness or weakness if anesthetic spreads near a nearby nerve, and, rarely, an allergic reaction to the contrast dye, anesthetic, or steroid. Repeated steroid injections are generally limited over a given period because of potential effects on nearby bone and soft tissue.

A well-performed diagnostic injection is a key branch point in care. A clear, reproducible reduction in your usual pain supports the SI joint as the pain generator and can guide next steps, which may include a therapeutic injection, radiofrequency ablation of the nerves supplying the joint, or, for carefully selected patients who have exhausted nonoperative options, minimally invasive SI joint fusion. A poor or inconsistent response suggests the pain may be coming from elsewhere and prompts your physician to look again at the lumbar spine or hip as possible sources.