Separated Shoulder

Overview

Shoulder instability is a condition in which one of the bones in the shoulder joint slides partially or completely out of place.

Normally, the head of the humerus, the upper arm bone, moves within the confines of the shoulder socket. Instability occurs when the head of the humerus slips outside its normal position. The head of the humerus may move in one or more directions. The disorder is classified by how much this bone moves and by the direction it moves:

• subluxation
  When the humeral head moves part way out of the shoulder socket.
  
  
• dislocation
  When the humeral head moves completely out of the socket.
  
  
• anterior
  When the humeral head moves toward the front. This is the most common form. It typically occurs in young men. Athletes with great shoulder flexibility are more prone to the disorder. Reinjury is more common in teens and young adults, because they have more elasticity in their shoulder capsule and ligaments. This can lead to later chronic instability.
  
  
• posterior
  When the humeral head moves toward the back. This is often caused by a severe muscle spasm during an electric shock or seizure. It less commonly happens as a consequence of direct trauma, which can lead to later chronic instability.
  
  
• multidirectional
  This usually occurs in athletes born with very loose joints. Certain sports that require great shoulder range of motion such as swimming may lead to multidirectional instability. In some instances, patients purposely contract or relax muscles to create an instability episode. This is sometimes associated with psychological problems.  
  

Shoulder instability often results from an initial acute injury producing a dislocation that, even with healing, leads to stretching of the shoulder capsule and ligaments. Such an injury could be due to falls or direct hits to the area. More rarely, shoulder instability develops slowly without any history of previous injury. In some cases, the shoulder may slip out of place at predictable times, such as when lifting a suitcase or even when shaving.

Risk factors for shoulder instability include:

• athletic activity, especially:
  

  baseball — pitching
  football — blocking
  gymnastics
  weight lifting
  tennis
  any contact sport
  volleyball
  swimming, especially backstroke or butterfly

• congenital collagen disorders, such as:
  

Marfan syndrome — a connective tissue condition
Ehlers-Danlos syndrome — a condition in which patients have loose joints

• family members with shoulder instability