Which rotator cuff muscle is an exception and inserts onto the lesser tuberosity?

The rotator cuff is comprised of four muscles that stabilize the shoulder joint: supraspinatus, infraspinatus, teres minor, and subscapularis. Each of these muscles has a specific insertion site on the humerus, with three of them inserting on the greater tuberosity, while one notably differs.

The subscapularis muscle is the exception as it inserts onto the lesser tuberosity of the humerus. This insertion point is critical because the subscapularis plays a vital role in the internal rotation and adduction of the shoulder. Its position allows it to effectively counterbalance the external rotators (infraspinatus and teres minor), thus contributing to the stability and movement of the shoulder joint.

In contrast, the other muscles—supraspinatus, infraspinatus, and teres minor—all insert onto the greater tuberosity. The supraspinatus is primarily responsible for initiating arm abduction, the infraspinatus facilitates external rotation, and the teres minor also assists in external rotation and adduction.

Understanding the unique insertion of the subscapularis helps in recognizing its specific functional contributions to shoulder mechanics and the clinical implications of rotator cuff injuries