Which muscle assists in external rotation and is located on the lateral border of the scapula?

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

Answer: (C)

External rotation of the shoulder is mainly produced by the posterior rotator cuff muscles. The clue about location points to teres minor, which originates along the lateral border of the scapula and inserts on the greater tubercle of the humerus. This positioning lets it help rotate the arm outward while also stabilizing the humeral head in the glenoid. While the infraspinatus also contributes to external rotation, it sits in the infraspinous fossa rather than along the lateral border, and the other two muscles are involved in different actions or locations (subscapularis anteriorly medially rotates; supraspinatus initiates abduction). Therefore, teres minor best fits both the action and the anatomical location described.