Anatomy and Biomechanics of the Sacroiliac Joint

Sacroiliac (SI) joint pain is a difficult problem that is becoming increasingly recognized for its contribution to low back pain. In certain circumstances it may present independently. However, in many scenarios the SI joint represents one of many factors contributing to axial back pain and its various referral patterns. Low back pain remains a significant burden on the health care system, accounting for ∼12 million physician office visits per year in the United States. It remains among the leading causes of disability, with expenditures in excess of $80 billion dollars every year. Surgical management of low back pain results in variable success rates ranging from 35% to 89%, suggesting that the etiology of back pain is complex, often multifactorial, and frequently not clearly known. Studies have shown that SI joint pathology may present in association with, or contribute directly to, back pain as often as 20% to 45% of the time. Despite this, the SI joint is often overlooked as a contributing source of back pain. It is necessary to maintain an index of suspicion, as well as understand the relevant anatomy, biomechanics, and clinical presentation involved in SI joint mediated pain, to be able to arrive at an appropriate diagnosis. This section presents a review of SI joint anatomy and biomechanics to establish a foundation necessary for understanding the clinical manifestations of SI joint dysfunction and treatment options.