The rotator cuff is a group of four tendons and their related muscles that cover the shoulder joint. The rotator cuff helps keep the shoulder stable and allows the arm to rotate or move up, down, in, and out.

Tendons are tough, ropelike fibers that connect muscles to bones. The rotator cuff muscles are called the supraspinatus, infraspinatus, subscapularis, and teres minor. Tendons connect the rotator cuff muscles, which start at the shoulder blade (scapula), to the upper arm bone (humerus).