Which muscle is not part of the rotator cuff?

The trapezius muscle is not considered part of the rotator cuff. The rotator cuff is primarily composed of four muscles that are crucial for shoulder stabilization and movement: the supraspinatus, infraspinatus, teres minor, and subscapularis. Each of these muscles originates from the scapula and inserts into the humerus, playing a significant role in maintaining shoulder joint integrity as well as enabling a variety of arm movements.

The trapezius, while important for shoulder function, has a different role; it is responsible for the movement of the scapula and plays a significant part in neck and shoulder movements. Therefore, it is anatomically and functionally distinct from the rotator cuff muscles. Understanding these differences is important in the context of shoulder injuries and rehabilitation, as rotator cuff injuries typically involve the four identified muscles, whereas trapezius-related issues would involve a different approach in assessment and treatment.