In Vivo Wear Performance of Total Hip Replacements with Oxinium Femoral Heads: A Retrieval Perspective

Introduction: Oxinium (OxZr) heads consist of zirconium with 2.5% niobium, and undergo a heat-treatment to obtain a 5μm-thick zirconia (ZrO2) layer. Most available data are based on in vitro tests while data on the in vivo performance are limited. The purpose of this study was to compare retrieved OxZr, ceramic and metal heads, considering their in vivo wear and corrosion behavior. Methods: This study included 35 OxZr heads with a short time in situ and roughly time-matched groups of 23 ceramic and 26 CoCrMo heads. All available stems and PE liners with minimal surgical damage were also examined. An optical coordinate-measuring machine was used to analyze the head bearing surfaces, liners and head and stem tapers. The liner damage was scored from 1-4 under a light-microscope based on the presence and severity of grooves/scratches, pitting/embedded debris, and polishing for a total possible score of 12. Selected OxZr heads’ areas and a cross-section of the ZrO2 layer were analyzed in a Scanning electron microscope (SEM). Retrieved capsule tissues of three patients with a damaged OxZr head were examined histologically and with SEM. Roughness measurements of heads and tapers were performed using a 3D Laser Confocal Scanning Microscope. Results: OxZr heads exhibited higher shape deviation compared to ceramic and metal. Despite extensive volume loss was not observed in most heads, tapers and liners, OxZr heads exhibited significantly higher volume loss compared to ceramic and metal. OxZr heads displayed pits on the bearing surfaces, while indents and cracking of the layer, associated with material transfer, were found on both bearing surfaces and head tapers. All tissues showed a benign response to OxZr debris, suggesting early-stage tolerance. The PE damage score was not different among head materials. Also, OxZr heads had proximal engagement, with minimal head taper damage compared to CoCrMo. Finally, OxZr heads had a significantly higher surface area roughness and presented Nb-rich regions in the substrate, in the ZrO2 layer and at their interface. Conclusion: OxZr heads seemed to outperform metal heads in corrosion resistance but appeared less favorable with respect to bearing surface wear performance compared to both metals and ceramics.