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Causes. The shoulder joint is the most frequently dislocated joint of the body. Because it moves in several directions, your shoulder can dislocate forward, backward or downward, completely or partially, though most dislocations occur through the front of the shoulder. dislocated shoulder may be caused by: 1  Sports injuries. 2  Shoulder dislocation is a common injury in contact sports, such as football and hockey, and in sports that may involve falls, such as downhill skiing, gymnastics and volleyball. 3  Trauma not related to sports.
Osteoarthritis (also referred to as degenerative joint disease or wear-and-tear arthritis) is caused by the breakdown of joint cartilage. Cartilage acts as a cushion between the bones that form a joint. Cartilage loss can cause bone to rub on bone in a joint -- a condition that is very painful. Usually osteoarthritis begins in a single joint. Rheumatoid arthritis is a chronic, inflammatory type of arthritis. It is also classified as an autoimmune disease (i.e., immune cells attack the body's own healthy tissues). The synovium (lining of the joint) is primarily affected by rheumatoid arthritis, but organs body-wide can be affected as well.