Measurement of the angle α.

Paraaxial (parallel to the axis of the femoral neck) reformation CT image in case 3. The angle α was defined by a line between the centre of the femoral head and the anterior point, where the distance of the centre of the femoral head exceeds the radius of the surface of the femoral head and a second line between the centre of the femoral head and the centre of the femoral neck at its narrowest point.