The Use of Europiumstearate to Trace Polyethylene Wear Debris in Joint Fluid after Prosthetic Joint Replacement - A Feasibility Study.

Ultra-high molecular weight polyethylene (UHMWPE) is the most common counterface material against metals or ceramics in artificial hip or knee joints. Wear and the resulting particulate debris, however, limit the life span of the implant. In this study, the general feasibility of using Europium (Eu) as tracer material to quantify UHMWPE wear in joint fluid is investigated. Using Inductively Coupled Mass Spectrometry (ICP-MS), recovery experiments of Eu in artificial joint fluid were performed. In order to dope polyethylene with 50 ppm Eu, nascent UHMWPE powder was mixed with a solution of Eu-stearate. The heterogeneity of the mixture was assessed by determining the coefficient of variation (CV) of the Eu content in various weighted samples. After molding of the UHMWPE powder mixture, cylindrical pins of 10 mm diameter were machined and worn against cobalt-chromium metal disks submersed in artificial joint fluid. The Eu-content of fluid samples taken at certain time intervals was measured and compared with UHMWPE weight loss of the pins. A satisfactory homogenization of Eu in the UHMWPE powder was achieved. Tracer-based and weight-loss determined wear rates were highly correlated (Pearson correlation coefficients > 0.991). Also the detection bias was within acceptable limits. Thus both methods demonstrated good agreement.