What most people call the shoulder is actually several joints that combine with tendons and muscles to allow a wide range of motion to the arm from scratching your back to throwing the perfect pitch. However, mobility has its price. It may lead to increasing problems with instability or impingement (ihm-PINJ-ment) of soft tissue, resulting in pain. You may feel pain only when you move your shoulder, or you may have endless discomfort. Sometimes the pain may be temporary and disappear in a short time, or it may continue and require medical diagnosis and treatment. Most shoulder problems involve muscles, ligaments and tendons, rather than bones. These problems fall into three major categories: tendonitis (ten-duh-NYE-tis), injury and arthritis. Tendonitis is a result of the wearing process that takes place over a period of years. Sometimes the bones in one of the shoulder joints move, or in an injury, are forced out of their normal position. This condition can result in the dislocation of one of the joints in your shoulder. There are many types of arthritis that can cause pain, but generally it involves wear and tear changes with inflammation of the joint, causing swelling, pain, and stiffness. Treatment for shoulder pain can involve altering activities, rest, and physical therapy to help you improve shoulder strength and flexibility. Your doctor may prescribe medication to reduce inflammation and pain. In some cases, injections of drugs may be used to treat pain.