Lower back pain is one of the most common conditions for which patients present for evaluation in health care. Sacroiliac (SI) joint dysfunction is an often overlooked source of lower back disease. This is especially true with mild or moderate SI joint arthritis because conventional radiographs may be inconclusive.1

The most common symptom of SI joint disease is buttock pain, and patients will often point directly to the SI joint as the point of maximum tenderness. The Fortin finger test is positive when the point of maximum tenderness is consistently within 2 cm inferior medial to the posterior superior iliac spine (PSIS).2

There is no single provocative test that is highly sensitive for diagnosing SI joint inflammation, but multiple positive tests (Table) help make the diagnosis. When more than 3 provocative tests are positive the predictive value approaches 80%.1

Table. Provocative Tests for SI Joint Pain2

FABER test/figure-4 test
Gapping/distraction test
Compression test
Thigh thrust test/femoral shear test
Gaenslen test/pelvic torsion test
Sacral thrust test/sacral base spring test

Computed tomography (CT) is the preferred imaging modality for the diagnosis of SI arthritis. Scan results, however, should be used with caution as 65% of patients with substantial SI joint degeneration will be asymptomatic.3

The best diagnostic modality is a therapeutic injection performed under fluoroscopic guidance.1 The pain generators can be both intra-articular and in the posterior SI joint ligaments. This has proven true as posterior periarticular injections in combination with intra-articular injections provide greater pain relief than intra-articular injections alone.1,3


1. Thawrani DP, Agabegi SS, Asghar F. Diagnosing sacroiliac joint pain. J Am Acad Orthop Surg. 2019;27(3):85-93. doi:10.5435/JAAOS-D-17-00132

2. Fortin JD, Falco FJ. The Fortin finger test: an indicator of sacroiliac pain. Am J Orthoped (Belle Mead, NJ). 1997;26(7):477-480.

3. Eno JJ, Boone CR, Bellino, MJ Bishop JA. The prevalence of sacroiliac joint degeneration in asymptomatic adults. J Bone Joint Surg Am. 2015;97(11):932-936. doi: 10.2106/JBJS.N.01101

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