Which rotator cuff muscle is primarily responsible for external rotation of the arm?

Which rotator cuff muscle is primarily responsible for external rotation of the arm?

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

Answer: (C)

External rotation of the arm is carried out mainly by the external rotators of the rotator cuff. The primary muscle responsible is the infraspinatus. It originates in the infraspinous fossa of the scapula and inserts on the greater tubercle of the humerus, so when it contracts it laterally rotates the humerus and helps keep the humeral head centered in the glenoid. Teres minor also contributes to external rotation, especially with the arm abducted, but it is smaller and acts as a synergist. The subscapularis, on the other hand, internally rotates the arm, and the supraspinatus is mainly involved in initiating abduction and stabilizing the joint rather than driving rotation.

External rotation of the arm is carried out mainly by the external rotators of the rotator cuff. The primary muscle responsible is the infraspinatus. It originates in the infraspinous fossa of the scapula and inserts on the greater tubercle of the humerus, so when it contracts it laterally rotates the humerus and helps keep the humeral head centered in the glenoid. Teres minor also contributes to external rotation, especially with the arm abducted, but it is smaller and acts as a synergist. The subscapularis, on the other hand, internally rotates the arm, and the supraspinatus is mainly involved in initiating abduction and stabilizing the joint rather than driving rotation.