[Pathomorphology of shoulder instability]

In cases of a traumatic anterior first-time dislocation of the shoulder, pathomorphological changes may initially occur at three different sites: at the capsule itself, at its origin or at its insertion. The typical injury is an avulsion of the labrum and the capsule from the glenoid and is called a Bankart lesion. There is a tendency to underestimate the amount of plastic deformation of the capsule and alternative injuries, such as avulsion of the capsule from the humeral head (HAGL lesion). Bony deformities at the humeral head or at the glenoid are of utmost importance for the prognosis of shoulder instability. In the dislocated position the anterior glenoid rim may notch the posterior surface of the humeral head (Hill-Sachs lesion). Bony defects of the glenoid may be caused by a fracture or due to chronic wear (fracture or erosion type). If bony defects exceed a certain size, isolated reconstruction of soft tissues does not guarantee stability of the shoulder.