Dislocation of the shoulder joint happens when the bones that make up the shoulder joint are moved apart so that the joint no longer functions. The shoulder is made up of two bones: the ball (the end of the arm bone, or humerus) and the socket (part of the shoulder blade, or scapula). When the ball part of the joint is dislocated in front of the socket, it is called an anterior dislocation. When it is dislocated behind the socket, it is called a posterior dislocation. In severe cases, ligaments, tendons, and nerves also can be stretched and injured.

The most common type of dislocation is an anterior dislocation. It can be caused by a fall onto the outstretched hand or shoulder. It may happen if the arm is forced into an awkward position. A posterior dislocation may occur as a result of a powerful direct blow to the front of the shoulder. It may also be caused by a violent twisting of the upper arm, such as that caused by an electric shock or seizure. Dislocated shoulders are common in contact sports such as football, rugby, hockey, etc.

The main symptom is pain in your shoulder and upper arm that is made worse by movement.

If you have an anterior dislocation, you will find yourself holding your arm on the dislocated side slightly away from your body with your opposite hand. This will keep your dislocated shoulder in the least uncomfortable position. Your shoulder will have a large bump rising up under the skin in front of your shoulder. Your shoulder will look square instead of round.

If you have a posterior dislocation, you will hold your arm on the dislocated side tightly against your body. You will have a large bump on the back of your shoulder.

This requires a physical exam to check for:

• shoulder tenderness and weakness
  
• numbness in the shoulder area, arm, or hand
  
• pain when you move your shoulder or loss of normal shoulder movement
  
• shoulder instability and deformity.

The first aid involves putting ice on the shoulder. Cold reduces swelling by controlling internal bleeding and the buildup of fluids in and around the injured area.

Prompt professional medical treatment should be sought for any suspected dislocation injury. A dislocated shoulder should be kept in its current position by use of a splint or sling. A pillow between the arm and torso may provide support and increase comfort. Normally, closed reduction, in which several methods are used to manipulate the bone and joint from the outside, is used. A variety of techniques exist, but some are preferred due to fewer complications or easier execution. In cases where closed reduction is not successful, surgical open reduction may be needed. Following reduction, X-Ray imaging is often used to ensure that the reduction was successful and there are no fractures. The arm should be kept in a sling or immobiliser for several days, preferably until orthopedic consultation.

Surgery: In some cases, surgery may be needed to get the shoulder repositioned correctly or if it continues to dislocate. If the shoulder joint becomes weak because of repeated dislocations, an operation may be recommended to tighten the ligaments that hold the joint together

Everyone recovers from an injury at a different rate. The goal of rehabilitation is to return to normal activities as soon as is safely possible. If the return is too soon one may worsen the injury.
One can safely return to activities when:

The injured shoulder has full range of motion without pain.
The injured shoulder has regained normal strength compared to the uninjured shoulder.