Anterior dislocation of the shoulder cup is the most common type of shoulder dislocation. In anterior dislocation, the ball of the shoulder moves to the front of the cup of the shoulder. The next common shoulder dislocation is posterior dislocation in which the ball goes behind the cup and is followed by a rare form of inferior dislocation in which the ball is under the cup. The anterior dislocation usually happens following a fall on an outstretched hand or if the arm is in an outward rotation. Posterior dislocation is rare but may happen in patients with seizure activity or electric shocks.