The rotator cuff is the group of four muscles and tendons that surround the shoulder joint, providing strength and stability. Above the rotator cuff there is a bursa, or sac of tissue, that covers and protects the rotator cuff as it comes into close contact with bones around the shoulder. When the rotator cuff is injured or damaged, it can lead to inflammation of the bursa, called bursitis, which causes pain and loss of motion.