Demonstration of a new technique using radioisotope tracers to measure the backside wear rate on tibial inserts

Local backside wear measurements on ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts in LCS mobile bearing knee prostheses have been performed using a new radioisotope tracing technique. The radioisotope tracers ⁹⁷Ru and ^101mRh were synthesized via a fusion evaporation reaction and recoilimplanted into cylindrical plugs of UHMWPE. The labelled plugs were carefully fitted into tibial inserts at two relevant locations. With bovine serum acting as a lubricant, the tibial inserts were then worn in vitro for 500,000 and 780,000 cycles, respectively, in a pneumatic knee motion simulator. Results reflect the non-linear change of wear during the wear-in phase and its evolution to a long-term steady-state rate. This new technique shows potential for extracting localized wear rates across the backside of a tibial insert in order to develop a comprehensive backside wear model.