Computer-based motion simulation of total hip prostheses with ceramic-on-ceramic wear couple. Analysis of implant design and orientation as influence parameters

Objective: In THA, ceramic-on-ceramic wear couples are increasingly used. A restricted range of motion (ROM) due to unfavourable implant design or positioning may cause impingement or dislocation, which can result in failure of ceramic inserts. Methods: By means of a 3-D CAD program different hip joint movements were simulated and the effects of ceramic hip implant design and position on the range of motion were analysed. Results: To offer sufficient ROM and to minimise risk of impingement and dislocation, inclination angle of the acetabular cup should be 45, cup anteversion 15 and stem antetorsion 0degrees to 10degrees. In regard to implant design, acetabular cups with slightly-recessed ceramic inserts should be used. Prosthetic systems with an elevated liner or with a mushroom-shaped femoral head are associated with limited ROM and increased risk of mechanical failure. The ratio of head to neck diameter should never be less than 2:1. Larger heads not only increase ROM, but also the stability of the prosthesis against dislocation. Thereby, the wear rate of ceramic-on-ceramic couples is not increased, in contrast to polyethylene. Conclusion: Considering certain criteria for ceramic hip implants regarding implant positioning, design and handling, ceramic-on-ceramic couples can be used with low risk of revision surgery and they can also reduce the prosthesis loosening associated with wear in young and active patients.