Which muscle helps stabilize the head of the humerus in the glenoid cavity during movement?

• A. Deltoid
• B. Latissimus dorsi
• C. Supraspinatus
• D. Pectoralis major

Answer: (C)

Pushing the humeral head into the glenoid to keep the ball centered in the socket is a job the rotator cuff does, especially when the arm moves. The supraspinatus sits on top of the shoulder blade and runs under the acromion to the humerus. When you start lifting the arm, it contracts to press the head of the humerus into the glenoid and prevent it from riding upward as the deltoid takes over lifting. This stabilizing squeeze is essential for smooth, safe movement across a range of shoulder activities, making supraspinatus the best choice.

Deltoid mainly lifts the arm and, without the stabilizing action of the rotator cuff, could contribute to upward movement of the head. Latissimus dorsi and pectoralis major move the arm in other directions and don’t provide the key compressive stabilization inside the joint during typical movements.