Rotator cuff tendonitis is caused by irritation and swelling of the tendons of the rotator cuff muscles. This may be due to an injury or overuse of the shoulder. It can occur in athletes who take part in throwing sports or in non-athletes who do regular heavy lifting or activities involving repetitive movements of the shoulder.
In rotator cuff impingement syndrome, the rotator cuff tendon becomes trapped and is repeatedly rubbed against the shoulder blade, leading to wear and tear of the tendon.
Rotator cuff tears are tears in the rotator cuff tendon instead of the muscles. It often happens as a result of a fall or an accident in younger people. In older people, tears are usually caused by rotator cuff impingement syndrome.