The image shows how to calculate the acetabular cartilage degeneration. The acetabular bony margin was used instead of the acetabular cup of total hip arthroplasty. Because the shape of the acetabulum is not spherical, three points that could be observed through the AP x-ray findings were selected: the acetabular superior-outer margin, inferior-inner margin and the point where the line that vertically bisects the line that connects the acetabular superior-outer and inferior-inner margin meets the acetabular bony margin. The wear program calculated the circle that passes through these three points.