Pain stemming from the SIJ is a common problem, in some series accounting for up to 30% of chronic low back pain.  Movement at the SIJ is limited except when under the influence of the hormone relaxin during pregnancy or in patients with hypermobility syndromes. 

Injury to the SIJ is usually the result of axial loading through an extended leg, with or without trunk rotation.  Risk factors include leg-length discrepancies, transitional anatomy of the L5 segment, bio-mechanical abnormalities and subsequent altered gait, scoliosis, spine surgery (particularly with fusion to the sacrum), and pregnancy. Pregnancy can predispose to SIJ-mediated pain by weight gain, increased lordosis, hormone-induced ligamentous laxity, and/or repetitive pelvic trauma.  Potential pain-generating structures in the SIJ and surrounding region include the joint capsule, subchondral bone, ligaments, entheses, and muscle.  

The precise innervation that carries these signals from the SIJ is complex and controversial, yet highly relevant to procedures performed to interrupt pain signals from the joint. The posterior aspect of the joint is likely innervated by the primary posterior rami of L5-S4, and the anterior aspect of the joint by the ventral rami of L5-S2. SIJ-mediated pain frequently (40%–50%) has an identifiable mechanical origin, which often distinguishes it from facet- or disc-mediated pain, including motor vehicle accidents, falls, repetitive stress, and pregnancy. The SIJ has variable referral patterns, possibly owing to its large size. The most common is pain in the buttock referring to the lateral thigh.  Radiation to the groin is less common (14%) yet is the most specific historical finding that helps separate SIJ-mediated pain from facets or discs.  Unilateral pain, the absence of lumbar pain, and pain upon rising from a seated position more commonly arise from the SIJ than discs or facet joints. The SIJ is the most likely source of pain when the worst pain is within 10 cm of the posterior superior iliac spine (PSIS).  One study reported that 28% ofpatients had pain from the SIJ that radiated below the knee, mimicking a radiculopathy. There are several physical examination maneuvers commonly used in clinical practice to establish the SIJ as the source of symptoms, including the Patrick, posterior shear, and resisted abduction test, but there is disagreement in the literature regarding their diagnostic utility. The pooled data from the individual studies fails to show any individual or cluster of tests that accurately predict the results of one or two diagnostic SI blocks. Overall, physical examination tests appear more effective at excluding than confirming the SIJ as a source of pain.  Using successful diagnostic blocks as a gold standard, computed tomography is 58% sensitive and 69% specific. A bone scan is less sensitive (13–46%) but more specific (90–100%).

Treatment of SIJ-mediated pain includes oral analgesics, physical therapy, supportive belts, injections in and around the SIJ, and radiofrequency ablations of the nerves innervating the SIJ.  Surgery is sometimes performed, particularly in cases of fracture, instability, and chronic pain.