Metastable Nature of Zirconia Femoral Heads From a 20-Year Perspective Of Clinical and Simulator Wear Studies

Clinical reports for zirconia-polyethylene total-hip replacements have been contradictory, and only a handful of retrieval studies have been performed. We review zirconia's mechanical properties, relevant clinical and retrieval studies, and discuss the "metastable" nature of the articular and taper-bore surfaces. Current limitations of wear-simulator studies are detailed. While some known parameters of phase transformation have been described, we lack understanding of how the different zirconia brand names, era of manufacture, ball diameters, clinical parameters, and exposure times in vivo will contribute to more or less phase transformation. As noted in recent clinical studies, patients with zirconia/polyethylene hip joint replacements may have to be monitored closely for adverse changes that have potential to occur 10 to 15 years post-operatively.