The teres minor is best described by which action?

• A. Medially rotate the shoulder
• B. Adduct the shoulder
• C. Extend the shoulder
• D. Laterally rotate the shoulder

Answer: (D)

Teres minor mainly enables external (lateral) rotation of the humerus at the shoulder. It sits on the posterior aspect of the scapula and attaches to the greater tubercle of the humerus, working together with the infraspinatus to rotate the arm outward and to help stabilize the humeral head in the glenoid during movement. This external rotation is most evident when the arm is at or above shoulder level, where teres minor contributes to fine control and joint stability.

Medially rotating the shoulder would move the arm inward, which is not the primary action of this muscle. Extending the shoulder involves moving the arm backward and is dominated by other muscles like the posterior deltoid and some back muscles. Adduction toward the midline is primarily handled by muscles such as the teres major and latissimus dorsi; teres minor can assist in some combined motions but is not described as the main action.