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Loss of normal half moon overlap sign

Dr Andrew Dixon and Radswiki et al.

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

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).