Which rotator cuff muscle is primarily responsible for externally rotating the arm?

Which rotator cuff muscle is primarily responsible for externally rotating the arm?

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

Answer: (A)

External rotation of the arm is powered mainly by the infraspinatus. This muscle sits on the posterior scapula and attaches to the greater tubercle of the humerus, pulling the humeral head laterally to rotate the arm outward. It provides the strongest external rotation torque across most angles of the shoulder and also helps stabilize the joint. Teres minor also assists with external rotation, especially when the arm is abducted, but it is smaller and contributes less overall. Supraspinatus is primarily involved in initiating abduction and stabilizing the joint, not external rotation, while subscapularis lies on the anterior surface and medially rotates the arm.

External rotation of the arm is powered mainly by the infraspinatus. This muscle sits on the posterior scapula and attaches to the greater tubercle of the humerus, pulling the humeral head laterally to rotate the arm outward. It provides the strongest external rotation torque across most angles of the shoulder and also helps stabilize the joint. Teres minor also assists with external rotation, especially when the arm is abducted, but it is smaller and contributes less overall. Supraspinatus is primarily involved in initiating abduction and stabilizing the joint, not external rotation, while subscapularis lies on the anterior surface and medially rotates the arm.