Shoulder dislocation classification

Anterior dislocation is usually the result of direct or indirect trauma, with the arm forced into abduction and external rotation. It is the most frequent type of shoulder dislocation (represents more than 90% of injuries).

In posterior dislocation, the humeral head is forced posteriorly in internal rotation. Posterior dislocations account for 2%–4% of all shoulder dislocations. In adults, convulsive disorder is the most common cause. Electrocution is a classic but uncommon cause of posterior shoulder dislocation. Bilateral dislocations are not infrequent.