The rotator cuff is composed of the following muscles and their associated tendons: supraspinatus, infraspinatus, teres minor and subscapularis. According to the MayoClinic.com website, rotator cuff injuries irritate or damage the rotator cuff muscles and tendons. One of the most common causes of rotator cuff injuries is repetitive overhead arm motion, such as throwing a baseball. Baseball pitchers are especially susceptible to rotator cuff injuries, and should take the necessary precautions to minimize the likelihood of injury.
Tendinitis & Bursitis
The MayoClinic.com states that the rotator cuff tendons can become inflamed as a result of overuse and overload, especially among athletes, such as baseball players, who perform repetitive overhead activities. According to the Joint Healing website, rotator cuff tendinitis, also known as bursitis or impingement syndrome, may occur when rotator cuff tendons experience irritation on the undersurface of the acromion--a bony outcropping of the shoulder blade that extends laterally over the shoulder joint. It's not entirely clear, though, what causes inflammation of the rotator cuff tendons. The Joint Healing website suggests that certain anatomical features, such as a hooked acromion, may predispose baseball players to rotator cuff tendinitis, or that the humerus or arm bone may ride up and pinch the cuff. In this latter scenario, the bursa--a fluid-filled sac that eases the friction between the rotator cuff and bone during movement--may become inflamed and cause pain.
Shoulder Instability
According to the American Academy of Orthopaedic Surgeons, shoulder instability occurs when the head of the humerus is forced out of the shoulder socket. Shoulder instability can result from a sudden, traumatic injury. It can also result from overuse of the shoulder ligaments, which is a more likely mechanism of injury for baseball players. The Joint Healing website notes that there are two principle classification of shoulder instability: dislocations and subluxations. Shoulder dislocations occur when the entire head of the humerus slips out of the shoulder socket, and usually is the result of significant trauma to the shoulder. Subsequent dislocation tend to occur with less and less force. Shoulder subluxations, states the AAOS, are a partial or incomplete dislocation of the head of the humerus from the shoulder socket. A dislocation of the shoulder's ball and socket or glenohumeral joint may eventually occur if a shoulder subluxation is present. The AAOS notes that even a minor injury may cause a shoulder subluxation injury.
Strain or Tear
According to the Sports Injury Clinic website, a baseball player who sustains an acute rotator cuff injury may feel a sudden tearing sensation in their shoulder, followed by marked pain throughout their arm and limited shoulder range of motion due to pain or muscle spasm. Players suffering a chronic rotator cuff tear, which typically develops over a prolonged period, will experience gradually worsening shoulder pain that's worse at night, and eventually will be unable to lift their arm away from their body without assistance. The Joint Healing website states that rotator cuff tears occur when shoulder tendinitis causes significant wearing of the rotator cuff tendons. Because the tendon is the link between the rotator cuff muscles and the humerus, if the tendon's integrity is compromised, shoulder weakness results. Although tears often occur in baseball players who have a history of shoulder pain, tears can happen to any player, regardless of their injury status.
