Which muscle is NOT a primary external rotator of the shoulder?

Which muscle is NOT a primary external rotator of the shoulder?

• A. Infraspinatus
• B. Teres Minor
• C. Posterior Deltoid
• D. Subscapularis

Answer: (D)

External rotation of the shoulder is driven mainly by the muscles on the back of the shoulder that pull the humerus outward. The key players are the infraspinatus and teres minor, which attach to the greater tubercle and rotate the arm outward while helping stabilize the joint. The posterior deltoid can assist with external rotation in certain positions, but its primary actions are shoulder extension and horizontal abduction, not a dedicated external rotator. Subscapularis sits on the front of the scapula and mainly internally rotates the humerus and stabilizes the joint, so it is not a primary external rotator.

External rotation of the shoulder is driven mainly by the muscles on the back of the shoulder that pull the humerus outward. The key players are the infraspinatus and teres minor, which attach to the greater tubercle and rotate the arm outward while helping stabilize the joint. The posterior deltoid can assist with external rotation in certain positions, but its primary actions are shoulder extension and horizontal abduction, not a dedicated external rotator. Subscapularis sits on the front of the scapula and mainly internally rotates the humerus and stabilizes the joint, so it is not a primary external rotator.