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Sternoclavicular dislocations are uncommon injuries and account for less than 3% of shoulder girdle dislocations.1 The medial clavicle may be displaced anteriorly or posteriorly. Anterior dislocations are more common by a ratio of 3:1 to 20:1.2,3 Case reports of the less common posterior dislocations are more common in the literature due to the higher incidence of associated complications. Posterior sternoclavicular joint dislocations are often seen in younger individuals.2,4

Sternoclavicular dislocations are the result of direct trauma to the sternoclavicular joint or to the glenohumeral joint with the force directed toward the sternoclavicular joint. This injury is usually associated with a tremendous force. The most commonly reported mechanisms of injury are motor vehicle collisions and contact sports.2,5 Anterior dislocations are often due to indirect forces transmitted through the anteromedial shoulder. As the shoulder is externally compressed and rolled backward, the lateral clavicle is pulled back and down beyond its limit of motion. The first rib acts as a fulcrum to spring the sternal end of the clavicle anteriorly from its articulation.2,6

Posterior dislocations may be due to direct or indirect forces.3,4,713 With indirect trauma, the shoulder is externally compressed and rolled forward from a posterolaterally applied force to the shoulder. The costoclavicular ligament acts as a fulcrum that produces displacement of the sternal end of the clavicle posteriorly from its articulation.4,9,11,13 Less commonly, a posterior dislocation may be due to a direct blow to the anteromedial clavicle.

There are reports of spontaneous and nontraumatic sternoclavicular subluxations and dislocations.14 These are usually seen in females less than 20 years of age with sternoclavicular joint laxity. The clavicle dislocates anteriorly during abduction or flexion of the arm to the overhead position. The clavicle reduces spontaneously when the arm is returned to the side. This condition is usually associated with laxity in numerous other joints.

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). ...

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