Establishment of the 3D femoral head weight-bearing area based on 2D X-ray radiograph

The setting of the weight-bearing area was based on the specific anatomical parameters of the X-ray AP view of the pelvis. Firstly, we calculated the magnification of the X-ray film by reference to standard marker (a coin), restored the actual size, and then identified 19 landmark points which included the following (Fig. ​(Fig.2):2): (1) point in the most lateral of the greater trochanter, (2) point in the top margin of the greater trochanter, (3) point in the most lateral of the femoral head, (4) point in the most lateral of the acetabulum, (5) point in the medial margin of sourcil line, (6) point in the most medial of the femoral head, (7) point in the inferior margin of the teardrop line, (8) midpoint of the line connecting the bilateral teardrop, (9) point in the center of pubic symphysis, (10) point in the inferior margin of the ischium, (11) point in the intersection between the posterior acetabular margin and inferior margin of the femoral head, (12) point in the most lateral of the ilium, (13) point in the inferior margin of the ilium, (14) point in the center of the fifth lumber vertebrae, (15) point in the inner margin of the ilium nearest to point 12, (16) point in the top margin of the femoral head, (17) point in the acetabular contour relative to point 16, (18) point in the lateral margin of teardrop relative to point 6, and (19) center of the femoral head. The calculation of anatomic parameters was referred to Genda et al., which based on the above landmark points: (a) lateral margin of the weight-bearing area (line 4–M): bisecting the angle 7–4–11 and (b) medial margin of the weight-bearing area (line 5-W): connecting point 5 and W (midpoint between points 6 and 18).

Identification of the anatomical landmarks on the AP radiograph to define the inner and outer edge of the weight-bearing area