A group of four tendons that stabilize the shoulder joint. Each of the four tendons hooks up to a muscle that moves the shoulder in a specific direction. The four muscles whose tendons form the rotator cuff are: • The subscapularis muscle, which moves the arm by turning it inward (internal rotation); • The supraspinatus muscle, which is responsible for elevating the arm and moving it away from the body; • The infraspinatus muscle, which assists the lifting of the arm during turning the arm outward (external rotation); • The teres minor muscle, which (like the infraspinatus) helps in the outward turning (external rotation) of the arm.