Fig. 1.

The method for determining the rotational center of a severely defective acetabulum is shown. A single plane is drawn containing three points: the mid-point of the line connecting the anterosuperior iliac spines, the center of the pubic symphysis, and the mid-point of the fifth lumbar vertebra. Then, a line perpendicular to the plane is drawn starting from the geometric center of the healthy femoral head and extended isometrically, allowing identification of the center of the diseased femoral head.