Figure 2: Femoral head appearance and image measurement. Note: (A) Appearance of intraoperatively-resected femoral head; (B) The center of the femoral head was incised longitudinally along the coronal plane with an electric pendulum saw to identify the central point of the femoral head. A line from the longitudinal axis of the femoral neck to the apex of the femoral head passes through the central point (X); the line (Y) perpendicular to X also passes through the central point. (C–F) X-ray film, computed tomography image, design sketch, and Digimizer® software image of the femoral head. b: distance between the central point along the X-axis and the apex of the femoral head; c: distance between the central point on the Y-axis and the apex of the lateral femoral head; a is finally identified based on b and c measurements. The angles between a and b, as well as a and c are 45°. a, b, c: the actual heights of the middle, medial, and lateral femoral heads after collapse, respectively.