An anatomic study of the subscapularis tendon and myotendinous junction.

The subscapularis muscle and tendon were studied in 25 cadaveric specimens. The subscaputaris insertion into the proximal humerus and its musculolendinous junction was defined. We found that the subscapularis muscle had a gradual formation of the musculotendinous junction and, in contrast to classical descriptions, inserted into the humerus as both tendon and muscle. The musculotendinous junction was fully formed 2 cm from the lesser tuberosity. The superior 60% of the muscle's insertion inserted into the lesser tuberosity as tendon. The remaining insertion consisted of muscle and was below the lesser tuberosity. The anterior humeral circumflex vessels and the axillary nerve marked the inferior aspect of the subscapularis muscle at the anterior aspect of the quadrangular space. The vessels then coursed laterally and superiorly onto the anterior surface of the muscle insertion coursing over the division between the tendinous and muscular portions. Proper identification of these relationships can prevent complications in shoulder surgery.