Metal ion release of a polished hip stem coated with a zirconium nitride multilayer in comparison with an uncoated hip stem - an in vitro study in a completely cemented as well as in a severe debonding condition.

Metal ion and particle release from cobalt-chromium alloys in total hip arthroplasty has been shown to induce metal hypersensitivity, adverse local tissue reactions and systemic ion-related diseases. The purpose of this study was to analyze the metal-ion-release barrier function of a cemented zirconium nitride (ZrN) multilayer-coated hip stem subjected to an axial sinusoidal load of 3.875 kN for 10 million cycles in a completely cemented and well-settled condition. An uncoated cobalt-chromium alloy stem was tested in the tribo-system with the surrounding bone cement mantle to provide reference values of a clinically established material. Moreover, the ZrN coated hip stems were also tested under a worst-case scenario, involving debonding from the bone cement mantle and high micromotions due to toggling against the cement mantle, to challenge the ZrN multilayer coating. Comparative analysis of ion concentration demonstrated a substantial reduction in the release of cobalt, chromium and molybdenum in the ZrN-coated stems against the uncoated version, even under the worst-case scenario of high micromotion by a severe implant debonding from the cement mantle.