The anterior sacroiliac ligaments are multiple short flat fibrous bands crossing the anterior surface of the sacroiliac joint, connecting the anterior sacrum to the adjacent ilium. They are the weakest of the sacroiliac ligaments, thinner and less robust than the interosseous and posterior SI ligaments. The lumbosacral trunk and upper sacral nerve roots cross the anterior sacrum immediately medial to the anterior SI ligament.
Provides anterior joint capsular reinforcement to the sacroiliac joint, limiting anterior sacral rotation relative to the ilium, and contributing to anterior pelvic ring stability in conjunction with the symphysis pubis.
Anterior sacroiliac ligament disruption occurs in the Tile type B2 (open-book pelvis injury) where external rotation forces open the anterior pelvis — the symphysis and anterior SI ligaments fail while the posterior ligaments may remain intact. Open-book injuries are treated by external fixation or anterior plating of the symphysis, restoring anterior SI ligament tension and reducing pelvic volume. The anterior SI ligament is accessed in anterior approaches to the sacroiliac joint for SI arthrodesis and for plate fixation of posterior pelvic ring disruption.
External rotation force to the pelvis sequentially disrupts the symphysis pubis and then the anterior sacroiliac ligament, producing an open-book pelvic injury with widened symphysis and anterior SI joint gap on AP pelvis radiograph; emergent pelvic binder and external fixator closure reduce pelvic volume and anterior SI tension while definitive fixation is planned.
