There are two major categories of shoulder instability; Traumatic & Multidirectional. The commonest instability pattern is Traumatic Anterior Dislocation. It is seen in patients who suffer an injury to their shoulder and dislocate out the front of the shoulder. These patients are often young males engaged in high impact sports. If they are young and remain active they will almost always redislocate their shoulders and usually they are troubled with recurrent dislocations. Modern treatment involves surgery to stabilise the shoulder and will usually be recommended after the very first dislocation.
Multidirectional instability is usually seen in people who are naturally very flexible. These people have what orthopaedic surgeons call ligamentous laxity, a condition in which the collagen is more stretchy than normal. The shoulder may dislocate out the back or the front and has often done so since the first dislocation.