INTRAARTICULAR CARCINOGENESIS BIOASSAYS OF COCRMO AND TIALV ALLOYS INRATS

Wear-debris powders of cobalt-chromium-molybdenum (CoCrMo) and titaniu m-aluminum-vanadium (TiAlV) alloys, which are widely used for orthoped ic implants leg, hip and knee prostheses), were tested for carcinogeni c activity following intraarticular administration (20 mg/rat) to grou ps of 44 male Fischer-344 rats (Charles River Breeding Laboratories, N orth Wilmington, MA). Control groups received similar intraarticular i njections of either a noncarcinogen (manganese powder, negative contro l rats) or a potent carcinogen (nickel subsulfide powder, positive con trol rats). The experimental groups of 8-12 rats were observed for 24 months after injection. No local tumors developed at the injection sit e in the negative control rats or in rats that received the CoCrMo or TiAlV powders; poorly differentiated or pleomorphic sarcomas developed at the injection site in 10 of the 12 positive control rats that were treated with nickel subsulfide. Incidences of primary tumors distant from the injection site did not differ significantly among the experim ental groups. This study shows that, under experimental conditions, an y carcinogenic activity of CoCrMo or TiAlV wear-debris powders is weak in comparison to nickel subsulfide. Based on this study and observati ons in other laboratories, intraarticular administration of test mater ials to rats provides a practical, reliable, and biologically relevant method for carcinogenesis testing of biomaterials used for orthopedic implants.