Fig. 1.

The patient was diagnosed with osteoarthritis in the right hip, and featured a normal left hip. Firstly, depending on the shape of femoral head surface, we fitted the most suitable sphere whose center was considered as the center of normal femoral head. With the aid of a symmetrical osseous symbol, such as anterior superior iliac spine, anterior inferior iliac spine and ischial tuberosity, we ascertained the mirror image plane according to the midpoints of three lines between symmetrical points. The center of abnormal femoral head was determined by the plane