Fig. 2A–H.

Our method of measuring femoral head roundness is shown. (A) The most superolateral and inferomedial points of the femoral head (a’ and a) in the coronal MR image were located where a line parallel to the femoral neck axis would be tangential to the femoral head. A base line was created by connecting these two points and divided into thirds. We then drew lines parallel to the femoral neck axis which ran through the 1/3 and 2/3 points on the baseline, and drew the best-fitting circles for the lateral third of the femoral head passing through points a′ and b′ (the point where the upper line parallel to the femoral neck axis meets the articular cartilage of the femoral head). The same approach was used for the medial third of the femoral head (not shown here). The length of the radius (r) for the best-fitting circle of the lateral third is termed the lateral head roundness (LHR), and the corresponding radius for the medial circle is the medial head roundness (MHR). (B) The same measurement methods were used to measure the radius (R) of the lateral third on the AP radiograph (using A and A’, and B and B’). (C) In the middle third, since any circle approximating it would be very large and subject to error, we defined central head height (CHH) as the height from the baseline, measured from its midpoint (m). (D) The same measurement method was used to measure CHH on the radiograph (M). (E) On the sagittal MR image, the anterior head roundness (AHR) and posterior head roundness (PHR) were measured using the same methods that were used in the coronal MR image. (F) On the lateral radiograph, AHR and PHR also were measured with the same methods that were used for the AP radiograph. (G) The CHH on the sagittal MR image was measured with the same method that was used for the coronal MR image. (H) The CHH on the lateral radiograph was measured with the same method that was used for the AP radiograph.