The shoulder is the most mobile joint in the body. It consists of a ball, the top of the humerus which fits into a socket of the shoulder blade called the glenoid. The socket is quite swallow and as a result the shoulder can turn in many directions.
To help stabilize the shoulder, there is a cartilage rim around the joint socket called the labrum which acts as a bumper to prevent the ball from slipping out of the socket. Also the shoulder contains a number of ligaments which further stabilize the joint and prevent dislocation. Furthermore, four muscles (rotator cuff muscles) surround the shoulder and contract to keep the shoulder joint reduced in its normal position.
Shoulder dislocation is the result of a traumatic injury, caused by extreme forces that stretch muscles, ligaments, and tendons. Sport injuries and vehicle accidents are prime causes of shoulder dislocations. The injury occurs when the top of the humerus is forced out of its socket.
The shoulder can either dislocate to the front (anterior dislocation) or the back (posterior dislocation). As the shoulder dislocates, it may tear a part of the cartilage rim and damage some of the ligaments surrounding the shoulder (often known as a Bankart lesion). In some cases there may be additional injury to the bone on the side of the glenoid, or the side of the humeral head (known as Hill-Sachs lesion).
Initial management of a shoulder rdislocation usually takes place in the Emergency Department. After adequate pain medication the shoulder is gently put back into place. Rarely, in more difficult cases the reduction is performed in the operating theatre under general anaesthetic.
After reduction of the shoulder the arm is placed in a sling for 1 week. Physiotherapy begins to strengthen the muscles and help stabilize the joint.
While physical therapy may help some, a good percentage of patients go on to dislocate their shoulder again.
Arthroscopic (key hole) surgery is used to reattach the torn cartilage rim to the socket and to tighten the ligaments around the shoulder.