The metaphyseal blanch sign of slipped capital femoral epiphysis.

In the early stage of slipping of the capital femoral epiphysis, the epiphysis slips posteriorly in relation to the neck of the femur. When this occurs, the posterior portion of the femoral head is seen on the anteroposterior radiograph as a crescent-shaped area of increased density overlying the metaphysis adjacent to the epiphyseal plate. This metaphyseal blanch sign suggests that slipping of the capital femoral epiphysis has occurred and that a lateral radiograph should be made to confirm or exclude the diagnosis.