Loss of normal half-moon overlap sign (shoulder)

Loss of half-moon overlap sign, which does not really roll off the tongue, is a sign of posterior shoulder dislocation on AP radiographs.

On a normal true anteroposterior image, there is a half-moon overlap between the humeral head and the glenoid. In a posteriorly dislocated shoulder, there is lateral displacement of the humeral head with respect to the glenoid (losing the half-moon overlap).