Sacroiliac Joint Dysfunction

SI joint pain is characteristically located just below and medial to the posterior superior iliac spine (PSIS). Key clinical features:

• Pain in the low back, buttock, or posterior thigh — typically one-sided
• Fortin finger test: The patient can point with one finger to the area of maximal pain, located within 1 cm below and medial to the PSIS — this is a positive Fortin finger sign, one of the most reliable clinical indicators of SI joint origin
• Pain that may radiate into the groin, posterior thigh, or below the knee (though distal referral is less common than with lumbar disc herniation)
• Aggravation with single-leg stance, prolonged sitting, getting in/out of a car, rolling over in bed, and climbing stairs
• Pain that is often worse on one side, particularly in patients with structural asymmetry

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No single clinical test reliably diagnoses SI joint dysfunction. However, a battery of provocation tests (when three or more are positive) has an 85% sensitivity and 79% specificity for SI joint pain:

• FABER test (Patrick's test): Hip flexion, abduction, external rotation in a figure-of-4 position. Pain in the posterior pelvis is positive for SI joint; groin pain suggests hip pathology
• FADIR test: Hip flexion, adduction, internal rotation, useful to rule out intra-articular hip pathology
• Gaenslen test: One hip in hyperextension with the other in flexion, stressing the SI joint; provocation of posterior pelvic pain is positive
• Compression test: Lateral compression of the iliac wings produces SI joint gapping and pain
• Distraction test: Anterior compression of ASIS produces posterior SI joint tension; posterior pelvic pain is positive
• Thigh thrust test: Posterior-directed force through the femur; one of the most sensitive individual SI joint tests

Imaging:

• Plain radiographs of the pelvis assess for inflammatory arthropathy, fracture, and gross joint changes
• MRI of the pelvis/SI joints identifies sacroiliitis, erosions, and inflammatory changes (important for ruling out ankylosing spondylitis and other spondyloarthropathies)
• CT scan provides superior detail of joint anatomy

Diagnostic SI joint injection under fluoroscopic guidance is the gold standard for confirming the SI joint as the pain source. Injection of local anesthetic into the joint (or periarticular ligamentous structures) with ≥75% concordant pain relief confirms the diagnosis. This diagnostic step also predicts response to subsequent therapeutic interventions.

Most patients with SI joint dysfunction achieve significant improvement with a combination of PT and targeted injections. The multi-modal approach (stabilization exercises, activity modification, and injection therapy) allows the majority of patients to return to full function. Lateral branch RFA provides longer-lasting relief for patients with confirmed joint-mediated pain. Long-term maintenance of hip and core strengthening is the most effective strategy for preventing recurrence.