The sacroiliac joint: anatomy, physiology and clinical significance

The sacroiliac joint (SIJ) is a putative source of low back pain. The objective of this article is to provide clinicians with a concise review of SIJ structure and function, diagnostic indicators of SIJ-mediated pain, and therapeutic considerations. The SIJ is a true diarthrodial joint with unique characteristics not typically found in other diarthrodial joints. The joint differs with others in that it has fibrocartilage in addition to hyaline cartilage, there is discontinuity of the posterior capsule, and articular surfaces have many ridges and depressions. The sacroiliac joint is well innervated. Histological analysis of the sacroiliac joint has verified the presence of nerve fibers within the joint capsule and adjoining ligaments. It has been variously described that the sacroiliac joint receives its innervation from the ventral rami of L4 and L5, the superior gluteal nerve, and the dorsal rami of L5, S1, and S2, or that it is almost exclusively derived from the sacral dorsal rami. Even though the sacroiliac joint is a known putative source of low back and lower extremity pain, there are few findings that are pathognomonic of sacroiliac joint pain. The controlled diagnostic blocks utilizing the International Association for the Study of Pain (IASP) criteria demonstrated the prevalence of pain of sacroiliac joint origin in 19% to 30% of the patients suspected to have sacroiliac joint pain. Conservative management includes manual medicine techniques, pelvic stabilization exercises to allow dynamic postural control, and muscle balancing of the trunk and lower extremities. Interventional treatments include sacroiliac joint, intra-articular joint injections, radiofrequency neurotomy, prolotherapy, cryotherapy, and surgical treatment. The evidence for intra-articular injections and radiofrequency neurotomy has been shown to be limited in managing sacroiliac joint pain.