The rotator cuff is a group of muscles and tendons that surround the shoulder joint. 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 and overuse the rotator cuff muscles. Examples include painters, carpenters, and people who play baseball or tennis. The risk of rotator cuff injury also increases with age.
Without treatment, rotator cuff problems may lead to permanent loss of motion or weakness, and may result in progressive degeneration of the shoulder joint. Although resting your shoulder is necessary for your recovery, keeping your shoulder immobilized for a prolonged time can cause the connective tissue enclosing the joint to become thickened and tight (frozen shoulder).
Many people recover from rotator cuff disease with physical therapy exercises that improve flexibility and strength of the muscles surrounding the shoulder joint.