The rotator cuff is a group of muscles and tendons that surround the shoulder joint, keeping the head of your upper arm bone firmly within the shallow socket of the shoulder. A rotator cuff injury can cause a dull ache in the shoulder, which often worsens when you try to sleep on the involved side.
Rotator cuff injuries occur most often in people who repeatedly perform overhead motions in their jobs or sports. Examples include painters, carpenters, and people who play baseball or tennis. The risk of rotator cuff injury also increases with age.
Many people recover from a rotator cuff injury with physical therapy exercises that improve flexibility and strength of the muscles surrounding the shoulder joint. Severe rotator cuff injuries, involving complete tears of the muscle or tendon, may require surgical repair.