Ligament · Pelvis

Posterior sacroiliac ligament

Ligamentum sacroiliacum posterius

A mass of short and long fibres filling the hollow behind the sacroiliac joint, running from the back of the sacrum outward and upward to the posterior superior iliac spine and the inner lip of the iliac crest. With the interosseous fibres deep to them these are the strongest ligaments in the pelvic ring, and they are the reason movement at the joint they cross is measured in millimetres rather than degrees. The longest fibres run downward and blend into the sacrotuberous ligament, so the two behave partly as one continuous sheet.