Which of the following is NOT a rotator cuff muscle?

The trapezius is not considered a rotator cuff muscle, which makes it the correct choice in this context. The rotator cuff consists of four specific muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles play a critical role in stabilizing the shoulder joint and facilitating shoulder movement. Each of the rotator cuff muscles has its own unique function, contributing to the dynamic stability of the shoulder by working together to hold the humeral head securely within the shallow glenoid cavity of the scapula during arm movements.

The trapezius muscle, on the other hand, is a large muscle that covers the upper back and neck and is primarily involved in movements such as shrugging the shoulders, moving the head, and extending the neck. It does not contribute to the stabilization of the shoulder joint in the same way the rotator cuff muscles do. Understanding the difference between these muscle groups is essential for grasping the mechanics and anatomy related to shoulder movement and injuries.