Which muscle resides on the anterior surface of the scapula and medially rotates the humerus?

• A. Subscapularis
• B. Infraspinatus
• C. Teres Minor
• D. Supraspinatus

Answer: (A)

The muscle on the anterior surface of the scapula that medially rotates the humerus is the subscapularis. It fills the subscapular fossa on the front of the scapula and inserts onto the lesser tubercle of the humerus, so when it contracts it pulls the humeral head inward, producing internal rotation. It also helps stabilize the shoulder joint as part of the rotator cuff. The other muscles listed sit on the posterior aspect or have different roles: them infraspinatus lies on the back of the shoulder blade and externally rotates the arm; teres minor is also posterior and externally rotates; supraspinatus sits above the spine of the scapula and initiates abduction, not medial rotation.