The shoulder is the most commonly dislocated joint. It accounts for approximately half (54.9%) of sports-related dislocations in high school athletes. The shoulder has the greatest range of motion of any joint in the body, placing it at risk for dislocation. The majority of shoulder dislocations (>95%) occur in an anterior and inferior direction.
Anterior dislocations commonly occur as a result of forceful abduction and external rotation. Posterior dislocations are less common and result from forceful internal rotation and adduction.
Source: Sports Health: A Multidisciplinary Approach May 2014