The rotator cuff is a group of tendons that connects the four muscles of the upper shoulder to the bones. The strength of the cuff allows the muscles to lift and rotate the humerus (the bone of the upper arm). The tendons run under the acromion (part of the shoulder blade) where they are very vulnerable to being damaged. This can lead to a tear resulting in a painful, weak shoulder.
The pain is very common at night, often radiating down the arm. As people age, it is normal for the rotator cuff tendon to wear and degrade, however only a small proportion of people develop pain and weakness that requires treatment.
A tear may result suddenly from a single traumatic event or develop gradually. When the tendons or muscles of the rotator cuff tear, the patient is no longer able to lift or rotate his or her arm with the same range of motion as before the injury and/or has significant pain associated with shoulder motion.

Causes

• Injury, especially while trying to lift or catch a heavy object
• Overuse, especially after a period of inactivity
• Poor blood supply to an area of the cuff (increases with age)
• Falling on an outstretched arm
• A gradual weakening of the tendons of the shoulder, often associated with impingement

Prevention

Avoid excessive overhead activities. Strengthen your shoulders and do not try to play or work through the pain.