Fig. 3

Measurements of the degree of joint motion of the bipolar prosthesis. According to the method described by Drinker and Murray (1979), the anteroposterior view was used to evaluate the abduction-adduction motion (a) and the lateral view was used to evaluate the flexion-extension motion (b): line 1 is parallel to the straight lateral edge of the outer cup, line 2 passes through the middle of the neck of the prosthesis, and line 3 is the acetabular index in the anteroposterior view and an extension of the upper margin of the sacrum in the lateral view. Angle 1–2 = inner motion; angle 1–3 = outer motion; angle 2–3 = total motion