The rotator cuff consists of four muscles--the supraspinatus, infraspinatus, subscapularis and teres minor. Each of these four muscles has an attachment from the shoulder blade (scapula) to the upper arm bone (humerus). The rotator cuff muscles function to stabilize the shoulder joint along with other surrounding structures (i.e. ligaments, labrum, and tendons). Additionally, these muscles act to rotate the arm inwardly (internal rotation) and outwardly (external rotation).