Fig. 1

a Hilgenreiner-epiphyseal angle is the angle between the Hilgenreiner line and a line connecting the medial and lateral end of the proximal femoral physis on the hip anteroposterior radiograph. Head-shaft angle is the angle between the proximal femoral shaft axis and a line which is drawn though the center of the proximal femoral epiphysis and perpendicular to the proximal femoral growth plate. Hilgenreiner-epiphyseal angle of the right hip is 6 degrees, and head-shaft angle of the left hip is 152 degrees on this radiograph. b Neck-shaft angle is the angle between the axis of the proximal femoral shaft and the axis of the femoral neck, which links the midpoints of neck diameter at both levels of the subcapital and the base of neck areas. Neck-shaft angle of the left hip is 140.5 degrees in this radiograph