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. It occurs most often in people who repeatedly perform overhead motions in their jobs or sports. Sometimes, rotator cuff tears may occur as a result of a single injury.
