Sacroiliac joint (SI joint)

The sacroiliac joint is a large, strong, amphiarthrodial joint at the base of the spine, where the sacrum meets the ilium of the pelvis. It is reinforced by a complex architecture of ligaments and surrounded by a fibrous capsule, with the joint cavity containing synovial fluid[1][2][4][5]. The joint allows very limited movement—primarily gliding and slight rotational movements—which are essential for stability, shock absorption, and weight distribution during activities such as walking, standing, or running[1][2][3][5]. In women, the joint becomes more flexible during pregnancy to facilitate childbirth[1][5]. Dysfunction or inflammation in the sacroiliac joint can lead to pain syndromes, often mistaken for other lumbar spine or hip issues[1][6]. It is not a molecular or therapeutic target like a receptor or enzyme, but rather an anatomical structure implicated in musculoskeletal disease states.

Other names

SI jointsacroiliac articulation