Differential hardness bearings in hip arthroplasty.

Second-generation metal-on-metal (MOM) bearing couples produce less wear debris than first-generation implants due to a better understanding of design parameters coupled with improved manufacturing processes. Wear debris generated by MOM bearings is extremely small compared with that from conventional metal-on-polyethylene bearings and can potentially be larger in number. Reductions in metal wear debris may be achieved by the use of differential hardness (DH) bearings for use with surface or total hip replacement implants. Laboratory testing has demonstrated that DH bearings exhibited less abrasive, adhesive, and surface fatigue damage than previous-generation MOM bearing couples. In addition, recent clinical trials have demonstrated a reduction in metal ion levels in patients who were implanted with a differential hardness bearing system. DH bearings may represent a third generation of hard bearing implants for use in hip replacement surgery that may potentially result in less complications and better success rates.