A sacroiliac (SI) joint injection is a procedure to inject local anaesthetic and corticosteroid into the SI joint under image guidance. It serves both as a diagnostic test (to confirm the SI joint as the source of buttock/low back pain) and as a therapeutic treatment.
Under fluoroscopic (X-ray) or CT guidance, a spinal needle is directed into the lower portion of the SI joint. Contrast dye is injected to confirm intra-articular position (arthrogram). A mixture of local anaesthetic and corticosteroid is then injected. The procedure takes 15–20 minutes. Ultrasound-guided approaches are also used.
Diagnostic: the gold standard for confirming SI joint dysfunction as the pain source. If the injection provides at least 50–75% relief, the SI joint is confirmed as the pain generator. Therapeutic: corticosteroid provides anti-inflammatory relief for SI joint arthritis, sacroiliitis (inflammatory or post-partum), and SI joint dysfunction.
Physiotherapy (SI joint mobilisation, core and pelvic stability exercises), SI joint belt, oral medication, radiofrequency denervation of lateral branch nerves (for longer-lasting relief), and prolotherapy.
Clinical suspicion of SI joint pain — typically one-sided buttock pain that may radiate to the groin or posterior thigh, reproduced by specific provocation tests (FABER, thigh thrust, compression, distraction). Outpatient procedure.
Diagnostic: confirms or excludes the SI joint as the pain source — invaluable for treatment planning. Therapeutic: corticosteroid provides relief lasting weeks to months in approximately 50–70% of patients.
Buttock soreness for a day or two.
Temporary pain increase for 24–48 hours.
Steroid effect may be temporary.
Septic arthritis of the SI joint. Very rare.
If the needle is positioned too anteriorly.
Inadvertent injection into pelvic vessels.
To contrast dye or corticosteroid.
Local anaesthetic at the skin. No sedation needed.
Normal activities immediately. Avoid heavy lifting for 24 hours. Record the pain response carefully — the diagnostic value is maximised by documenting the degree and duration of pain relief.
Record the pain response at the time of injection and over the following 48 hours. Report to the clinical team. If positive, further treatment (SI fusion, radiofrequency denervation) is planned based on the response.
SI joint pain is notoriously difficult to diagnose clinically. The injection is the gold standard — if numbing the joint relieves the pain, the joint is confirmed as the source. This is why diagnostic injection is so valuable.
Most clinicians limit to two to three per year. If injections provide reliable but temporary relief, SI joint fusion or radiofrequency denervation may offer more durable benefit.