Rotator Cuff Injuries.
The rotator cuff is a group of muscles and tendons that cover the head of the humerus and hold it in the shoulder socket. When rotator cuff tendons become damaged, the shoulder can become stiff, sore or lose mobility. Injuries are often caused by direct damage, such as a traumatic fall or repetitive overhead motions. It can also develop because of indirect causes such as impingement or shoulder imbalance.