The sacroiliac joint is a bicondylar synovial joint that is formed by the articulation between the sacrum and ilium (Fig. 133.1). The articular surface of the sacrum is covered with hyaline cartilage, with the articular surface of the ilium covered with fibrocartilage. The articular surfaces are characterized by irregular elevations and depressions that allow the joints to interlock at numerous points along their articular surface contributing to joint strength. The joint’s articular cartilage is susceptible to damage from overuse or misuse, which, if left untreated, will result in arthritis with its associated pain and functional disability. Osteoarthritis of the joint is the most common form of arthritis that results in sacroiliac joint pain and functional disability, with rheumatoid arthritis, spondyloarthropathies, and posttraumatic arthritis also causing arthritis of the sacroiliac joint. Less common causes of arthritis-induced sacroiliac joint pain include the collagen vascular diseases, infection, villonodular synovitis, and Lyme disease. Acute infectious arthritis of the sacroiliac joint is best treated with early diagnosis, with culture and sensitivity of the synovial fluid, and with prompt initiation of antibiotic therapy. The collagen vascular diseases generally manifest as a polyarthropathy rather than a monoarthropathy limited to the sacroiliac joint, although sacroiliac pain secondary to the collagen vascular diseases responds exceedingly well to ultrasound-guided intra-articular injection of the sacroiliac joint. Occasionally, the clinician encounters patients with iatrogenically induced sacroiliac joint dysfunction due to overaggressive bone graft harvesting for spinal fusions.

Patients with sacroiliac joint pain secondary to strain or arthritis-related pain complain of pain that is localized to the sacroiliac and proximal lower extremity. The pain of sacroiliac joint strain or arthritis radiates into the posterior buttocks and the back of the legs (Fig. 133.2). The pain does not radiate below the knees. Activity makes the pain worse, with rest and heat providing some relief. The pain is constant and characterized as aching. Sleep disturbance is common with awakening when the patient rolls over onto the affected sacroiliac joint. Spasm of the lumbar paraspinal musculature often is present,
as is limitation of range of motion of the lumbar spine in the erect position that improves in the sitting position due to relaxation of the hamstring muscles. Patients with pain emanating from the sacroiliac joint exhibit a positive Yeoman test. The Yeoman test is performed by flexing the knee to 90 degrees and then hyperextending the hip, putting stress on the sacroiliac joint (Fig. 133.3). A positive test is indicated by the production of pain around the sacroiliac joint.

Plain radiographs are indicated in all patients who present with sacroiliac pain as not only intrinsic sacroiliac disease, as well as other regional pathology may be perceived as sacroiliac pain by the patient (Fig. 133.4). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound of the sacroiliac is indicated if the diagnosis is in question or infection of the joint is a possibility.

The sacroiliac joint is a bicondylar synovial joint that is formed by the articulation between the sacrum and ilium (see Fig. 133.1). The articular surface of the sacrum is covered with hyaline cartilage, with the articular surface of the ilium covered with fibrocartilage. These articular surfaces have corresponding elevations and depressions, which give the joints their irregular appearance on radiographs (Fig. 133.5). The strength of the sacroiliac joint comes primarily from the posterior and interosseous ligaments, rather than from the bony articulations (Fig. 133.6). The sacroiliac joints bear the weight of the trunk and are thus subject to the development of strain and arthritis. As the joint ages, the intra-articular space narrows, making intra-articular injection more challenging. The ligaments and the sacroiliac joint itself receive their innervation from L3 to S3 nerve roots, with L4 and L5 providing the greatest contribution to the innervation of the joint. This diverse

innervation may explain the ill-defined nature of sacroiliac pain. The sacroiliac joint has a very limited range of motion, and that motion is induced by changes in the forces placed on the joint by shifts in posture and joint loading.