Fig. 1A–B.

(A) The THA model, which can be moved in six dimensions (flexion, extension, abduction, adduction, internal rotation, and external rotation), allows observation of bone-bone impingement and implant impingement. (B) A goniometer was set to this apparatus with the precision of ± 1° in each measurement. In all measurements, a femoral head with a 28-mm diameter and +3 mm neck length was used. Springs were placed at the femoral installation site with a force of 20 N to keep the acetabular and femoral components attached. A 52-mm acetabular component was fixed at 45° abduction.