The rotator cuff muscles hold the head of the long bone of your upper arm tightly in the socket of your shoulder. Sports that require moving the arm over the head repeatedly can cause tearing and swelling of the tendons of these muscles. Baseball pitchers, swimmers, weight lifters and tennis players often suffer this injury. Chronic irritation can cause pain, swelling and tearing of the rotator cuff. If you continue to exercise in spite of the pain, you will tear the tendons from their attachments.
Initially, pain occurs only when you hold your arm over your head and bring it down or forward forcibly. Later, it will hurt when the arm is moved forward for any reason, such as to shake hands. Usually, it hurts when you push things away and does not hurt when you pull objects toward you. A torn rotator cuff will cause tenderness over the tendons, especially when the elbow is raised above the shoulder. It will hurt when you pull your arm across your chest, and you will have difficulty raising your elbow over your shoulder. An arthrogram is often not sensitive enough to diagnose a partial tear of the rotator cuff but can show a complete tear.
The treatment is to avoid any motion that hurts and strengthen the uninjured shoulder muscles. Do weight-lifting exercises that bring the weights toward the body and do not hurt, such as upright rows and downward "lat pulls". You may need surgery if the rotator cuff tendons are torn completely, or if the tendons do not heal within one year.