Which muscle lies on the scapula below the spine and laterally rotates the humerus, stabilizing the shoulder?

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

Answer: (C)

Lying in the infraspinous fossa just below the spine of the scapula, this muscle is the infraspinatus. Its main job is to externally (laterally) rotate the humerus and to help stabilize the shoulder by keeping the head of the humerus centered in the glenoid during movement. It’s part of the rotator cuff, working with the other cuff muscles to maintain joint stability.

Supraspinatus sits above the spine and mainly initiates arm abduction. Teres minor also contributes to external rotation but runs along the lateral border of the scapula, not in the infraspinous fossa. Subscapularis lies on the anterior surface of the scapula and medially rotates the humerus.