Effect of cup abduction angle and head lateral microseparation on contact stresses in ceramic-on-ceramic total hip arthroplasty

A finite elements model was developed in order to evaluate the combined influence of the head lateral microseparation and the cup abduction angle on the contact pressure in Ceramic-on-Ceramic Total Hip Arthroplasty. The model's parameters were those used on the Leeds II hip simulator. A 32 mm head diameter and a 30 μm radial clearance was used. The cup was positioned with an abduction angle ranging from 45° to 90°. The medio-lateral microseparation varied from 0 to 500 μm. A load of 2500 N was applied through the head centre. For 45° abduction angle, edge loading appeared above a medial-lateral separation of 30 μm. Complete edge loading was obtained for a 60 μm medial-lateral separation. Under edge loading conditions, the contact area was found to be elliptical. For 45° abduction angle, as the head lateral separation increased, the maximal contact pressure increased from 66 MPa and converged to an asymptotic value of 205 MPa. Both cup abduction and lateral microseparation displacement induced a large increase in the stresses in Ceramic-on-Ceramic THA. However, this increase in contact pressure induced by higher abduction angle, became negligible as the lateral separation increased.