The sternoclavicular joint is a diarthrodial joint with both surfaces covered by fibrocartilage (Figure 80-1). The intraarticular disk ligament divides the joint into two separate compartments, each of which is lined with synovium.15 This joint is freely movable and functions almost like a ball-and-socket joint in that it has motion, including rotation, in almost all planes.3,6,16 This includes 30° to 35° of upward elevation, 35° of combined forward/backward movement, and 40° to 45° of rotation about its long axis.3,6,16 Less than half of the medial clavicle articulates with the upper angle of the sternum. This gives the sternoclavicular joint the distinction of having the least amount of bony stability of any of the major joints.3 Given this amount of joint incongruity, it is surprising that sternoclavicular joint dislocations are uncommon. However, its stability comes from strong surrounding ligaments (Figure 80-1). These ligaments include the intraarticular disk ligament, the extraarticular costoclavicular ligament (rhomboid ligament), the anterior and posterior sternoclavicular ligaments, and the interclavicular ligament.15