Which muscle is primarily responsible for abduction of the shoulder?

The muscle primarily responsible for abduction of the shoulder is the supraspinatus. This muscle is part of the rotator cuff group and plays a crucial role in the initial phase of shoulder abduction. Specifically, the supraspinatus initiates the first 15 degrees of motion, after which the deltoid muscle continues the abduction movement.

Understanding the anatomy of the shoulder can provide clarity on the function of the supraspinatus. It originates from the supraspinous fossa of the scapula and inserts onto the greater tubercle of the humerus. When the supraspinatus contracts, it pulls the humeral head upward and outward away from the body, facilitating arm movement away from the midline.

In contrast, the other muscles listed have different primary functions. The infraspinatus and teres minor assist in shoulder external rotation rather than abduction, while the subscapularis is predominantly involved in internal rotation. Thus, the specific role of the supraspinatus in initiating shoulder abduction makes it the correct answer.