The rotator cuff is made up of four muscles that help control shoulder motion. Three of the four muscles (supraspinatus, infraspinatus, and teres minor) control external rotation of the shoulder while the subscapularis muscle performs internal rotation. These muscles attach to the bones via tendons that help stabilize the shoulder joint.

This group of muscles can be damaged in many different ways. One common cause is inflammation with tendinitis, bursitis, or arthritis of the shoulder due to degeneration with age. Inflammation of or around the rotator cuff muscles can result in extra stress and pressure on the muscles leading to pain and breakdown. Another common cause of rotator cuff dysfunction is trauma such as from falling, sports, or overuse. Repetitive overhead movements is the most frequent action associated with dysfunction. Rotator cuff symptoms consist of shoulder pain, tenderness with touch, and decreased range of motion for external rotation. Dysfunction can range from mild to severe depending on rotator cuff status and symptoms.

Sources: medicinenet.com