The shoulder joint is the most frequently dislocated major joint of the body. In a typical case of a dislocated shoulder, either a strong force pulls the shoulder outward (abduction) or extreme rotation of the joint pops the ball of the humerus out of the shoulder socket. Dislocation commonly occurs when there is a backward pull on the arm that either catches the muscles unprepared to resist or overwhelms the muscles. When a shoulder dislocates frequently, the condition is referred to as shoulder instability. A partial dislocation in which the upper arm bone is partially in and partially out of the socket is called a subluxation.

Signs and symptoms: The shoulder can dislocate either forward, backward, or downward. When the shoulder dislocates, the arm appears out of position. Other symptoms include pain, which may be worsened by muscle spasms; swelling; numbness; weakness; and bruising. Problems seen with a dislocated shoulder are tearing of the ligaments or tendons reinforcing the joint capsule and, less commonly, bone and/or nerve damage.

Diagnosis: Doctors usually diagnose a dislocation by a physical examination; x rays may be taken to confirm the diagnosis and to rule out a related fracture.

Treatment: Doctors treat a dislocation by putting the ball of the humerus back into the joint socket, a procedure called a reduction. The arm is then stabilized for several weeks in a sling or a device called a shoulder immobilizer. Usually the doctor recommends resting the shoulder and applying ice three or four times a day. After pain and swelling have been controlled, the patient enters a rehabilitation program that includes exercises. The goal is to restore the range of motion of the shoulder, strengthen the muscles, and prevent future dislocations. These exercises may progress from simple motion to the use of weights.

After treatment and recovery, a previously dislocated shoulder may remain more susceptible to re-injury, especially in young, active individuals. Ligaments may have been stretched or torn, and the shoulder may tend to dislocate again. A shoulder that dislocates severely or often, injuring surrounding tissues or nerves, usually requires surgical repair to tighten stretched ligaments or reattach torn ones.

• Sometimes the doctor performs surgery through a tiny incision into which a small scope (arthroscope) is inserted to observe the inside of the joint. After this procedure, called arthroscopic surgery, the shoulder is generally stabilized for about 6 weeks. Full recovery takes several months. Arthroscopic techniques involving the shoulder are relatively new, and some surgeons prefer to repair a recurrent dislocating shoulder by time-tested open surgery under direct vision. Usually following open surgery there are fewer repeat dislocations, and movement is improved, but there is often some loss of motion.