Shoulder Instability


Shoulder instability occurs when the upper-end of the arm bone, known as the humerus, slides partially or completely out of the shoulder socket.The disorder is classified by how much the humerus moves and the direction of the movement:
  • Subluxation—The humeral head moves partially out of the shoulder socket.
  • Dislocation—The humeral head moves completely out of the socket.
  • Anterior—The humeral head moves toward the front.
  • Posterior—The humeral head moves toward the back.
  • Inferior—The humeral head drops downward.
  • Multidirectional—The humeral head moves toward difference places.
Shoulder Instability
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Shoulder instability often results from injury.

Risk Factors

Factors that may increase your chance of shoulder instability include:
  • Trauma, such as a fall with an outstretched arm or a direct blow to the shoulder
  • Previous shoulder dislocation
  • Athletic activity, especially:
    • Baseball—pitching
    • Football—tackling
    • Tennis
    • Gymnastics
    • Weight-lifting
    • Any collision or contact sport
    • Volleyball
    • Swimming, especially backstroke or butterfly
  • Congenital collagen disorders, such as:
  • Family members with shoulder instability


Symptoms may come on suddenly or develop over time. Shoulder instability may cause:
  • Pain in the shoulder area
  • Shoulder or arm weakness
  • Shoulder may feel loose
  • Shoulder may slip out of place
  • Numb feeling down the arm

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