an orthopedic implant with a diffusion - hardened surface on non - load bearing areas of the implant for interaction with non - load bearing surfaces of a polymeric bio - compatible material , such as uhmwpe . the orthopedic implant is a mobile - bearing knee prosthetic and system where a coating of oxidized zirconium is formed on the post of the tibial tray of the prosthetic for interaction with an opening of a polymeric tibial insert . the diffusion - hardened surface of the orthopedic implant provides a strengthened post and reduction in wear in the opening of the polymeric insert .