Abduction

• The supraspinatus muscle is the major muscle in the rotator cuff. It sits at the top of the scapula -- shoulder blade -- and the tendon travels over the head of the humerus and attaches to the front. It is most frequently torn, and it is prone to tendonitis as well. The supraspinatus muscle is responsible for lifting the arm into abduction -- in a straight plane out to the side. When this tendon is torn, a person will attempt to elevate his arm but will instead shrug up at the shoulder as other muscles try to compensate. If this tendon is not repaired quickly, this altered motion can be difficult to correct because the muscles learn to function improperly.
  
  

External Rotation

• The infraspinatus and teres minor muscles move the shoulder into external rotation -- outward rotation. This motion is necessary for throwing a ball, reaching up for a seat belt, washing your hair and reaching behind your head. The infraspinatus muscle originates on the scapula below the supraspinatus muscle, and the teres minor originates at the outside border of the scapula.Their tendons travel over the top of the humerus and attach to the bone and the joint capsule. These tendons are torn less frequently than the supraspinatus, but they can be torn by traumatic rotator cuff injuries.
  
  

Internal Rotation

• The subscapularis muscle moves the shoulder into internal rotation -- inward rotation. This movement is important for reaching into your back pocket, tucking in your pants, putting on a jacket and sports such as swimming. This muscle originates on the front side of the scapula, and the tendon travels to the front of the humerus. Ruptures of the subscapularis tendon are rare.
  
  

Treatment

• Full-thickness rotator cuff tears require surgical intervention to reattach the tendon to the bone. If a significant amount of time passes between the injury and the surgery, the tendon retracts -- shortens -- and a tendon graft is used. Partial-thickness tears -- incomplete tears -- can heal over time and are frequently treated with physical therapy and cortisone shots.
  
  Rotator cuff rehabilitation includes range-of-motion exercises, strengthening, education about proper workplace ergonomics and body mechanics, and modalities such as heat, ultrasound and electrical stimulation.