20 Year Experience of Zirconia Total Hip Replacements

Total hip replacements have used zirconia balls with polyethylene (PE) cups from the 1st generation, pioneering era (1985-1995), the 2nd generation HIPed and proof-tested product (1995-2001) and the 3rd generation alumina-doped zirconia (2000-). The yttria-stabilized zirconia (Y-TZP) has shown controversial performance in both laboratory and clinical studies. The zirconia combination alone (Zr/Zr) and combined with alumina ceramic (Zr/Al) has rarely been used due to concerns of degradation with long-term use. In the laboratory the Zr/PE combinations generally showed the least wear compared to CoCr/PE and Al/PE. However the greatly differing thermal conductivity between such ball materials may have had a major effect in-vitro, with serum-lubricated wear studies. It is likely that the 1st generation, non-HIPed zirconia balls have predominated in Zr/PE results reported to date. Clinical studies with Zr/PE bearings have shown mixed results. Generally speaking the wear rates, osteolysis and revision rates for Zr/PE combinations have been adversely higher compared to conventional CoCr/PE and Al/PE series. Retrieval studies also showed many variations with increased roughness of Zr-balls from 10nm to 250nm and monoclinic transformation detected from 10% to 85%. Revision rates have varied from zero to 70% with long-term follow-up, although there were many confounding differences in implant design and quality of PE cups. There do not appear to be studies detailing the performance with the 2nd generation HIPed zirconia ball, or the 3rd generation, alumina-doped zirconia ball that is reputed to have overcome the risk of metastability challenges. Introduction