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Sternoclavicular Joint

The SC joint is the only true joint that connects the upper extremity to the axial skeleton. It is a gliding joint with little inherent bony stability. Substantial incongruity exists between the two articular surfaces, but the interposition of an intra-articular disc compensates for this. This disc has not shown severe degenerative alterations until the seventh decade of life, but even then, the joint seems to be well preserved.

The SC joint is enveloped in a loose, fibrous capsule that blends with the margin of the disc. The stability of the joint, which is provided mainly by the surrounding ligaments, protects the important underlying vasculature, pleural domes, trachea, and esophagus. The SC ligaments consist of the anterior and posterior SC and capsular ligaments, the interclavicular ligaments, and the anterior and posterior costoclavicular ligaments.

These allow motion in all planes, including rotation. The SC ligaments prevent upward displacement of the medial clavicle caused by downward forces on the lateral end of the clavicle. The posterior capsular ligament is the most important stabilizer. These ligaments allow the clavicle to move 30 degrees upward, 30 degrees in an anteroposterior direction, and rotate 45 degrees about its long axis.

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