The rotator cuff is a collection of muscles that provide the shoulder joint with stability during rotation. The American Academy of Orthopaedic Surgeons (AAOS) states that rotator cuff injuries are one of the most common causes of shoulder pain, and the incidence of these injuries increases with age. The risk of injury is highest in certain athletes, such as swimmers, baseball pitchers and kayakers. Symptoms of a injury to the rotator cuff may include severe pain in the arm or shoulder, limited movement of the shoulder joint, weakness and pain in the shoulder that becomes worse at night. In most cases, surgery is not necessary, and rotator cuff injuries are treated with rest, ice, and anti-inflammatory medications.