The posterior connection of the pelvic girdle is a paired articulation called the sacroiliac articulation. It occurs between the auricular surface of the sacrum and the similarly named surface of the ilium, and is only slightly moveable. The rough irregular surfaces of the two bones are scarcely adapted for reciprocal movements, and the strong ligaments surrounding the articulation further insure its immobility. In addition to being connected by the synovial auricular surfaces, the os coxae and the sacrum are also held together by a strong ligament passing between the tuberosities of the two bones, the interosseous sacroiliac ligament. Since this ligament completely fills the space between the tuberosities of the ilium and the sacrum, it may be said that these two bones are connected anteriorly by an synovial joint and posteriorly by a syndesmosis.

Articulatio sacroiliaca

Articulation sacroiliaque