The femoral head notch.
A notch-like defect at the vertex of the proximal femoral ossification center is a normal variant in children. This has often been mistaken for Legg-Perthes disease. This sharply defined defect is distinct from the irregular epiphyseal ossification patterns common in other areas.
D002648:Child; D002675:Child, Preschool; D005270:Femur Head / Q000000981:diagnostic imaging*; D006801:Humans; D007873:Legg-Calve-Perthes Disease / Q000000981:diagnostic imaging; D008297:Male; D010012:Osteogenesis; D011859:Radiography