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Diagnostic Injections
SI Joint Injection
An injection into the joint between the spine and pelvis to test whether it is causing low back or buttock pain.
For information only — not medical advice. The content on this page is patient education to help you understand a condition or treatment. It is not a substitute for personalised assessment by a qualified clinician. Always consult your doctor or specialist about your own symptoms, diagnosis, and treatment decisions.
What it is
A sacroiliac (SI) joint injection places local anaesthetic (often with a steroid) into the joint where the base of the spine meets the pelvis. The SI joint can be a source of low back and buttock pain, but it is difficult to assess by examination alone and frequently looks normal on scans. The injection is used mainly to test whether this joint is responsible for a person's symptoms.
How it works
Because the pain from the SI joint overlaps with other causes of low back pain, numbing the joint directly is one of the more reliable ways to test its involvement: if the pain substantially eases after the joint is anaesthetised, the SI joint is likely to be the source. The joint has an irregular shape and lies deep, so imaging guidance — usually X-ray screening, sometimes ultrasound or CT — is used to place the needle accurately, often with a little contrast dye to confirm it is within the joint.
What to expect
You lie face down while the skin is numbed and the needle is guided into the joint under imaging. You may feel pressure or a brief reproduction of your usual pain. The procedure takes only a few minutes. Afterwards you will be asked to record how your pain responds over the following hours, as this is what gives the test its diagnostic value. The team will provide after-care advice, and you may need to arrange transport home.
Why it matters for spinal investigations
SI joint problems are easily overlooked because they mimic other causes of low back pain and often do not show clearly on standard scans. A diagnostic SI joint injection can confirm the joint as a genuine source of pain when other tests are inconclusive, opening the way to focused treatment. It is a practical way of testing a structure that is otherwise hard to pin down.
References & further reading
- —NICE — Low Back Pain and Sciatica in Over 16s (NG59)
- —Faculty of Pain Medicine, Royal College of Anaesthetists — Standards
- —British Association of Spine Surgeons (BASS)
This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.
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