Supraspinatus

• The supraspinatus muscle originates on the top of the scapula (shoulder blade), above the spinous process and inserts on the top of the head of the humerus. It is responsible for abduction---raising the arm sideways.
  
  

Infraspinatus

• The infraspinatus originates in the depression, or fossa, in the triangular part of the scapula, below the spinous process and inserts in the middle of the head of the humerus. It is responsible for external rotation, turning the arm away from the body. It also stabilizes the humerus in the shoulder girdle.
  
  

Teres Minor

• The teres minor originates on the lower, exterior border of the scapula and inserts on the bottom of the head of the humerus. Like the infraspinatus it is responsible for external rotation and stabilization.
  
  

Subscapularis

• The subscapularis originates on the interior side of the scapula, next to the rib cage, and inserts on the bottom of the head of the humerus. It is responsible for internal rotation---turning the arm inward, and stabilization.
  
  

Common Rotator Cuff Injuries

• Common rotator cuff injuries include tears, sprains and tendinitis. Due to the specialized function of the rotator cuff muscles, injuries are a serious matter and should be examined to ensure proper function of the shoulder girdle.