Fig. 4

Measurement of the vertical-center-anterior margin (VCA) angle on the sagittal plane. The VCA angle is measured according to the method of Needell et al. [14]. a Reference standard axial plane for measuring the VCA angle. Solid line is drawn 25° obliquely from the most anterior lateral margin of the acetabulum, which is identified on the axial plane at the opening of the acetabulum. b Reconstructed 25° oblique sagittal plane (solid line in a). θ6 is the VCA angle, which is measured between the line joining the anterior aspect of the weight-bearing zone and the hip center and the perpendicular line from the femoral head center