A sacroiliac joint injection is a procedure that delivers medication directly into or around the sacroiliac (SI) joint, one of two joints that connect your lower spine to your pelvis. It serves two purposes: diagnosing whether the SI joint is actually the source of your pain, and treating that pain with anti-inflammatory medication. The total volume injected is small, typically 1.5 to 4 mL, and the procedure itself usually takes only minutes.
Where the Injection Goes
You have two SI joints, one on each side of your body, sitting where the triangular bone at the base of your spine (the sacrum) meets the large pelvic bones. These joints don’t move much, but they bear a significant amount of force when you walk, bend, or shift weight from one leg to the other. Pain-sensing nerve fibers from the lower spine and upper sacral area supply the joint, which is why SI joint problems can produce deep, aching pain in the low back, buttock, or upper leg.
The injection can be placed directly inside the joint capsule (intra-articular) or into the ligaments and tissues surrounding it (peri-articular). Research increasingly shows that intra-articular injections produce better therapeutic results than peri-articular ones, so most practitioners aim to get the needle inside the joint space.
Diagnostic Versus Therapeutic Injections
SI joint pain is notoriously difficult to diagnose. No single physical exam test or imaging scan can reliably confirm it. That’s where diagnostic injections come in. A numbing agent is injected into the joint under image guidance, and if your pain drops significantly within minutes, the SI joint is confirmed as the source.
Most pain management guidelines require at least 75% pain relief from the numbing agent for the injection to count as a positive diagnostic result. However, more recent evidence suggests that patients who experience 50% to 74% relief may still benefit from further SI joint treatments like joint fusion. Insurance coverage typically allows up to two diagnostic injection sessions before moving to a treatment plan.
Therapeutic injections use the same approach but add a corticosteroid, a powerful anti-inflammatory, alongside the numbing agent. The goal shifts from identifying the problem to reducing inflammation and providing longer-lasting pain relief. Current reimbursement guidelines allow up to four therapeutic injection sessions per 12-month period, whether the injections are on one side or both.
What Gets Injected
The medication cocktail is straightforward. A local anesthetic provides immediate numbness, which also serves as the diagnostic test. When the injection is purely diagnostic, the total volume is around 2 mL. When a corticosteroid is added for therapeutic purposes, the volume increases to roughly 3 mL.
The corticosteroid component is what provides weeks of relief by calming inflammation inside and around the joint. Different practitioners use different steroid formulations, but all work on the same principle: suppressing the inflammatory process that irritates the joint’s pain-sensing nerves.
How Imaging Guides the Needle
Because the SI joint is deep, irregularly shaped, and surrounded by dense ligaments, practitioners use real-time imaging to guide the needle into the correct spot. The two most common methods are fluoroscopy (a type of live X-ray) and ultrasound.
A randomized controlled trial comparing the two approaches in 40 patients with chronic low back pain from SI joint arthritis found no significant difference in pain scores at one month or at any other follow-up point. Both groups experienced meaningful pain reduction from baseline. Procedure time, patient discomfort, and satisfaction were also comparable. The practical takeaway: both guidance methods work well, and your provider’s choice often comes down to equipment availability and personal expertise.
How Much Relief to Expect
The numbing agent kicks in within minutes, which is how the diagnostic portion works. The corticosteroid takes longer, typically a few days to reach its full effect.
A study tracking patients after fluoroscopically guided steroid injections found significant pain reduction at both 2 weeks and 8 weeks after the procedure. Patients whose injection reached the upper portion of the joint experienced a greater drop in pain at 2 weeks, though this advantage leveled out by 8 weeks. The relief is real but temporary. SI joint injections are not a cure; they reduce inflammation for a period of weeks to months, buying time for physical therapy or other treatments to address the underlying problem.
Some patients get enough relief from a single injection to complete a rehabilitation program and maintain improvement on their own. Others need repeat injections at intervals throughout the year. The four-session annual limit reflects the goal of providing meaningful relief without overexposing the joint to corticosteroids, which can weaken tissue over time with repeated use.
Risks and Side Effects
Serious complications from SI joint injections are rare. The most commonly reported immediate event is a vasovagal reaction, a brief episode of lightheadedness or fainting triggered by the needle, occurring in about 2% of patients. Transient headache affects roughly 0.8% of people who receive SI joint injections specifically.
Temporary numbness or weakness in the leg can happen if the anesthetic spreads to the nearby sciatic nerve, which runs close to the joint. This occurs in up to 5% of patients and resolves on its own as the numbing agent wears off. It’s uncomfortable and can be alarming, but it’s not a sign of nerve damage. Infection is a possibility with any injection but is exceedingly uncommon with proper sterile technique and image guidance.
What the Procedure Feels Like
You’ll lie face down on a procedure table. After cleaning the skin over the affected joint, the provider numbs the surface with a small injection of local anesthetic. You’ll then feel pressure as the guided needle advances toward the joint. Some people feel a deep ache or brief sharp sensation as the needle enters the joint capsule. The medication injection itself takes only seconds.
Most people spend 15 to 30 minutes in a recovery area afterward. You’ll be asked to move around and rate your pain to assess the diagnostic response. Because of the numbing agent, your leg may feel slightly weak or heavy for a few hours, so having someone drive you home is standard. Activity restrictions after an injection are minimal compared to surgical procedures. Most people return to desk work the same day or the next, with a short period of avoiding heavy lifting or intense exercise for 24 to 48 hours while the steroid begins working.
When Injections Are Not Enough
If steroid injections provide consistent but short-lived relief, your provider may discuss longer-term options. Radiofrequency ablation uses heat to interrupt the nerve signals carrying pain from the joint, offering relief that can last six months to a year or more. SI joint fusion is a surgical option that permanently stabilizes the joint, typically reserved for patients who have confirmed SI joint pain through diagnostic injections but haven’t responded adequately to conservative treatments. The diagnostic injection is often the gateway to these decisions: it establishes the SI joint as the pain generator, which then opens the door to more targeted interventions.