REDUCTION OF METAL ION RELEASE IN DUAL MOBILITY AND IN CEMENTED TOTAL HIP ARTHROPLASTY

Zirconium nitride (ZrN)-multilayer coating is clinically well established in total knee arthroplasty [1–5] and has demonstrated significant reduction in polyethylene wear and metal-ion release [4–5]. However, its introduction to total hip arthroplasty (THA) has to be investigated, as in this articulation the multilayer coating has micromotions against hard materials such as bone cement or titanium. The objective was to analyse the biotribological behaviour and metal-ion release of a ZrN-multilayer coating on CoCr28Mo6 alloy dual-mobility inserts and polished CoCr28Mo6 cemented hip stems, designed for patients with suspected metal-ion hypersensitivity. CoCr28Mo6 alloy dual-mobility inserts (Plasmafit ® DM) and hip stems with ZrN-multilayer coating (CoreHip ® AS) were tested versus uncoated versions. The dual-mobility THA articulation system was tested in bovine serum in a test set-up consisting of a titanium alloy cup, dual-mobility insert, vitamin E stabilized polyethylene and ceramic head. The test set-up was positioned under steep cup (55° inclination) and acetabular bone defect condition and tested with a cyclic load of 5,340 N for 10 million cycles. Metal-ion concentration of Co, Cr, Mo was measured by inductively-coupled-plasma mass-spectroscopy (ICP-MS) after 1,3&10 million cycles. The coated hip stems were tested in a worst-case-scenario with ceramic heads in bovine serum in a severe cement interface debonding condition under a cyclic load of 3,875 N for 15 million cycles. After 1,3,5,10&15 million cycles the surface texture was analysed by scanning-electron-microscopy (SEM) and energy-dispersive x-ray (EDX). Metal-ion concentration of Co, Cr, Mo was measured by ICP-MS after each test interval. Results. Based on SEM/EDX-analysis, it has been demonstrated that the ZrN-multilayer coating keeps its integrity over 15 million cycles of severe stem cemented interface debonding without any exposure of the CoCr28Mo6-substrate. For the ZrN-multilayer coated dual-mobility inserts and hip stems, the cobalt-ion concentration released by diffusion through the porosity of the multilayer-coating was two orders of magnitude lower in comparison to their uncoated versions. The ZrN-multilayer coated CoCr28Mo6 alloy dual-mobility inserts and the polished cobalt-chromium cemented hip stem have a significant reduction of cobalt-ions, even under severe stem debonding and high interface micromotion conditions. ZrN-multilayer coating on cobalt-chromium hip implants might be a suitable option for further minimization of metal-ion release in THA.