The sacroiliac joint

Abstract

Many old editions of Gray’s Anatomy described the sacroiliac joint as diarthrodial but partly united by patches of soft fibrocartilage and fine interosseous fibres. Later editions described it as being a synovial joint marked by a number of irregular elevations and depressions, providing a locking device restricting movement and contributing to the stability of the joint. Only in the elderly, and particularly in the male, is it usual to find that the joint cavity is at least partly obliterated by the presence of fibrous or fibrocartilaginous adhesions. This change of attitude ascribing a certain amount of movement to the joint followed reports in the 1920s which clearly showed movement of a gliding and rotatory nature. By the 1950s Weisl (1955) had investigated the movements of the sacroiliac joint by radio-graphic methods in the living subject. He identified the axis of rotation and showed that its site was variable. Pitkin and Pheasant (1936) described the movement of the ilia about the symphysis pubis causing torsion of the pelvis thought to occur during walking. The innominate on one side is rotated backwards on the sacrum and that on the other side, forwards. In order for this movement to take place, sometwisting must take place atthe symphysis pubis. As the range of movement of the sacroiliac joint is small and varies according to the circumstances and to the subject, it is not surprising that there has been little agreement regarding the function of this joint and the significance of its movement. There is no evolutionary evidence from other species of a tendency towards fusion of these joints. Helfet and Lee (1978) believe that the main function of the joint is probably as a shock-absorber, to prevent reactive forces from the limbs reaching the spinal column.