The influence of metallic shell deformation on the contact mechanics of a ceramic-on-ceramic total hip arthroplasty

Total hip arthroplasty of ceramic-on-ceramic bearing combinations is increasingly used clinically. The majority of these implants are used with cementless fixation that a metal-backing shell is press-fitted into the pelvic bone. This usually results in the deformation of the metallic shell, which may also influence the ceramic liner deformation and consequently the contact mechanics between the liner and the femoral head under loading. The explicit dynamic finite element method was applied to model the implantation of a cementless ceramic-on-ceramic with a titanium shell and subsequently to investigate the effect of the metallic shell deformation on the contact mechanics. A total of three impacts were found to be necessary to seat the titanium alloy shell into the pelvic bone cavity with a 1 mm diameter interference and a 1.3 kg impactor at 4500 mm s^-1 velocity. The maximum deformation of the metallic shell was found to be 160 μm in the antero-superior and postero-inferior direction and 97 μm in the antero-inferior and postero-superior direction after the press-fit. The corresponding values were slightly reduced to 67 and 45 μm after the ceramic liner was inserted and then modified to 74 and 43 μm under loading, respectively. The maximum deformation and the maximum principal stress of the ceramic liner were 31 μm and 144 MPa (tensile stress), respectively, after it was inserted into the shell and further increased to 52 μm and 245 MPa under loading. This research highlights the importance of the press-fit of the metallic shell on the contact mechanics of the ceramic liner for ceramic-on-ceramic total hip arthroplasties and potential clinical performances.