Shoulder instability can be a common problem following a shoulder dislocation. After the first violent injury that causes the shoulder to dislocate, the joint may remain unstable. This can result in repeated episodes of dislocation, even during normal activities.  The risk of repeated dislocation is much higher in people aged under 25.

Sometimes the shoulder does not come completely out of the socket but slips partially out and then returns to its normal position. This is called subluxation. In some cases, instability may be present without an initial dislocation. The initial injury may not have been sufficiently severe to cause a dislocation or all the joints may be hyper-lax due to a genetic problem with the connective tissue of the body.

97% of dislocations are anterior, meaning that the humerus slips out of the front of the shoulder socket.  Only 3% dislocate posteriorly, or out the back.

A shoulder dislocation  is usually very obvious. The injury is usually very painful and the shoulder looks abnormal. A dislocated shoulder may cause damage to the nerves around the shoulder joint; this is usually temporary. Subluxation of the shoulder usually causes a quick feeling of pain, like something is slipping, or pinching, in the shoulder.

The diagnosis of shoulder instability relies on the history and physical examination. For the dislocated shoulder, x-rays are also necessary to rule out a fracture of the shoulder. X-rays are usually done after the shoulder is relocated as well, to make sure it is back in place and no fractures are present.