Dislocated Shoulder

Medical Author: Benjamin C. Wedro, MD, FACEP, FAAEM
Medical Editor: Melissa Conrad Stöppler, MD

• What is dislocation of the shoulder? What causes a shoulder dislocation?
• What are the symptoms and signs of a dislocated shoulder?
• How is a dislocated shoulder diagnosed?
• How is a dislocated shoulder treated?
• What happens after reduction of a shoulder dislocation?
• What is appropriate follow-up following a shoulder dislocation?
• What are potential complications of a shoulder dislocation?
• Shoulder Dislocation At A Glance
• Find a local Orthopedic Surgeon in your town

What is dislocation of the shoulder? What causes a shoulder dislocation?

The shoulder joint is the most mobile joint in the body and allows the arm to move in many directions. This ability to move makes the joint inherently unstable and also makes the shoulder the most often dislocated joint in the body.

The head of the humerus (upper arm bone) sits in the glenoid fossa, an extension of the scapula, or shoulder blade. Because the glenoid fossa (fossa = shallow depression) is so shallow, other structures within and surrounding the shoulder joint are needed to maintain its stability. Within the joint, the labrum (a fibrous ring of cartilage) extends from the glenoid fossa and provides a deeper receptacle for the humeral head. The capsule tissue that surrounds the joint also helps maintain stability. The rotator cuff muscles that move the shoulder also provide a significant amount of protection for the shoulder joint.

Dislocations of the shoulder occur when the head of the humerus is dislocated from its socket. These are described by the location of the humeral head after it has been dislocated. Ninety percent or more of shoulder dislocations are anterior dislocations, meaning that the humeral head has been moved to a position in front of the joint. Posterior dislocations are those in which the humeral head has moved backward toward the shoulder blade. Other rare types of dislocations include luxatio erecta, an inferior dislocation below the joint, and intrathoracic, in which the humeral head gets stuck between the ribs.

Dislocations in younger people tend to arise from trauma and are often associated with sports or falls. Older patients are prone to dislocations because of gradually weakening of the ligaments and cartilage that supports the shoulder.

Anterior dislocations often occur when the shoulder is in a vulnerable position. A common example is when the arm is held over the head with the elbow bent, and a force is applied that pushes the elbow backward and levers the humeral head out of the glenoid fossa. This scenario can occur with throwing a ball or hitting a volleyball. Anterior dislocations also occur during falls on an outstretched hand. An anterior dislocation involves external rotation of the shoulder; that is, the shoulder rotates away from the body.

Posterior dislocations are uncommon and are often associated with specific injuries like lightning strikes, electrical injuries, and seizures. On occasion, this type of dislocation can occur with minimal injury in the elderly, and often the diagnosis is missed in this case.