An image-guided injection into the joint between the sacrum and the pelvis. It is often the only way to confirm that joint is the culprit.
What it is
The sacroiliac joint cannot be injected with any confidence without imaging. Blind injections miss the joint a large share of the time. Under fluoroscopy (live X-ray), contrast dye confirms the medicine is really inside the joint.
PRP and the other orthobiologics we use for the low back and pelvis are explained on our PRP injections in St. Louis page.
What is an SI joint injection used for?
- Sacroiliac joint pain
- Low back pain after a fall onto the buttock
- Lasting one-sided low back pain after lumbar fusion
What happens during an SI joint injection?
- You lie face down; the joint is entered under X-ray guidance.
- Takes about 15 minutes.
- It is both a test and a treatment. The pattern of relief tells us a great deal.
- No sedation; most patients drive themselves home.
What are the risks of an SI joint injection?
Risks specific to this joint come first. The sacral nerve roots lie nearby, so short-lived leg numbness or heaviness afterward is possible. Contrast confirms the needle is inside the joint. So a technically unsuccessful injection (a miss) is caught during the procedure, not guessed at later from a poor result. Soreness over the joint for a day or two after the shot is usual.
To talk about whether this is right for you, call us or request an appointment.
How do you know if an SI joint injection worked?
This is one of the few procedures that is truly both test and treatment. No exam test or scan can reliably pin down this joint. So your response to a confirmed intra-articular injection (one inside the joint) is the diagnosis.
Relief that is complete but brief points toward lateral branch blocks and ablation. Relief that is partial but lasting often argues for repeating it, along with exercises to steady the pelvis.
Before and after your procedure
No sedation is used, so most patients drive themselves home. Transient leg heaviness is possible; if a leg feels weak or numb, have someone else drive until that wears off. Keep a note of your pain over the next hours and days. With this joint the response is the diagnosis, so the record matters. Avoid heavy lifting for two days. Soreness over the joint for a day or two is expected.
Related: when injections and ablation stop working for a confirmed joint, sacroiliac joint fusion is the next step to discuss.
How the procedure is actually done
The sacroiliac joint is a true synovial joint (a joint with a lining that makes fluid). It sits at an odd, slanted angle that differs from person to person. That is why blind injection into it is unreliable. Under fluoroscopic guidance, the needle goes into the lower third of the joint, where the capsule can be reached. Contrast confirms it has entered the joint and not the soft tissue behind it.
Who it suits, and who it does not
It suits patients whose exam points to the sacroiliac joint. That means pain over the joint itself, often into the buttock and at times the back of the thigh. Specific provocation tests (moves that stress the joint) bring the pain on. It is not the first step for midline low back pain. It is a test as much as a treatment. What the joint tells us in the hours after the injection guides what comes next.
How success is measured
What you can do is the measure, not a number on a scale. That means distance walked before symptoms, hours slept, tasks taken back up, and medicine needed. We record those before treatment and compare them after. A procedure that moves a pain score for two weeks and changes nothing you can do has not done much. Repeating it is rarely the answer.
Common questions
Why can’t the joint be injected without imaging?
Its angle varies a great deal from person to person. So blind injections often end up outside the joint, and the result cannot be read.
Is sacroiliac pain visible on an MRI?
Usually not. The joint often looks normal on imaging even when it is the whole problem. That is why the injection is the test.
Sacroiliac Joint Pain goes through it in detail.
What if it helps only briefly?
Brief but strong relief is a positive diagnostic result. It points toward ablation of the lateral branches as the longer-lasting option.
Sacroiliac Joint Radiofrequency Ablation goes through it in detail.
Can I drive myself home after an SI joint injection?
Yes, most patients can. No sedation is used, so most patients drive themselves home. The sacral nerve roots lie close to the joint, so temporary leg numbness or heaviness is possible after the injection. If a leg feels weak or numb, have someone else drive until that wears off. Normal activity, including work, resumes within two to four hours.
What should you not do after an SI joint injection?
Avoid heavy lifting for two days. Do not skip the pain record. Note how you feel over the next hours and days, because with this joint the response to the injection is the diagnosis. And do not read brief relief as failure. Brief but strong relief is a positive result. It points toward ablation of the lateral branches as the longer-lasting option.
How long does it take to recover from an SI joint injection?
Recovery is short. The injection takes about 15 minutes. Soreness over the joint for a day or two is usual, and you should avoid heavy lifting for two days. Any leg numbness or heaviness from the nearby sacral nerve roots is temporary. Keep a note of your pain over the following hours and days, because that pattern of relief decides what comes next.
Sources
- McCormick ZL et al. Consensus practice guidelines on sacroiliac joint complex pain from a multispecialty, international working group. Pain medicine (Malden, Mass.), 2025. PubMed 41318933
- Szadek K et al. 5. Sacroiliac joint pain. Pain practice : the official journal of World Institute of Pain, 2024. PubMed 38155419
- Bresnahan JJ et al. Review of Sacroiliac Joint Injection Techniques. Current pain and headache reports, 2022. PubMed 35239155
- Soto Quijano DA et al. Sacroiliac Joint Interventions. Physical medicine and rehabilitation clinics of North America, 2018. PubMed 29173661
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