The cobalt-chromium-molybdenum alloy designated standard specification F- 75 by the American Society for Testing and Materials (ASTM) is the most commonly used alloy in orthopedic prostheses for total and partial joint replacement. The F-75 alloy is hard, stable, and corrosion resistant. Its wear in joint replacement prostheses is not a problem per se. However, wear of the mating ultrahigh molecular weight polyethylene (UHMWPE) on which the metallic part articulates is a well documented chronic problem. A number of recent publications (1,2) have reported that UMHWPE wear debris is observed in the interface between the hip stem and femor in cemented total hip replacement. The UHMWPE wear debris is, therefore, partially blamed for bone desorption and eventual loosening of the F-75 alloy femoral component. Ion implantation is an innovative surface process modification process that can readily be applied to finished F-75 alloy prostheses. Preliminary research at Spire Corporation has shown that ion implantation of biologically inert species such as nitrogen and carbon increases hardness and reduces the friction of F-75 alloy. The harder, more lubricous F-75 alloy is expected to significantly reduce wear of the UHMWPE component.
