Anteroposterior radiographs of the pelvis were used to measure the lateral centre-edge-angle (LCA) and the acetabular angle of Hilgenreiner (AA). To measure the LCA, a best fitting circle inside the femoral head was drawn. The angle was then measured between two lines from the centre of this circle, one vertically and the other one to the lateral acetabular edge. The AA was measured by using the angle between the Hilgenreiner’s line (line through both triradiate cartilage) and the acetabular roof.