The interosseous sacroiliac ligament is a ligament of the sacroiliac joint that lies deep to the posterior ligament, and consists of a series of short, strong fibers connecting the tuberosities of the sacrum and ilium. It is the strongest ligament in the body. The major function of the interosseous sacroiliac ligament is to keep the sacrum and ilium together and therefore prevent abduction or distraction of the sacroiliac joint.