CARCINOGENICITY OF COCRMO (F-75) IMPLANTS IN THE RAT

A long-term study was conducted in rats to assess the contd bution of the surface area of CoCrMo devices to carcinogenesis. Groups consistin g of 104 rats each (52 male, 52 female) were either implanted with met al cylinders fixed on the left, lateral femur (groups 1-3) or injected with a suspension of metal microspheres in the dorsal subcutis (group 4). Group 1 (control) received solid Ti6Al4V cylinders [surface area to body weight (SA/BW) ratio measuring 1.35 times that of human total hip prosthesis (HTHP)]. Group 2 was implanted with solid CoCrMo (SA/BW ratio: identical to implants of group 1). Group 3 received sintered-p orous CoCrMo devices (SA/BW ratio: 30 x HTHP). Group 4 was injected wi th a suspension of CoCrMO microspheres (SA/BW ratio: 135 x HTHP). Impl ant-associated humors (IATs) were observed in 23, 14, 3, and 15 rats o f groups 1, 2, 3, and 4, respectively. Within groups 1 and 2, 34 IATs were associated with loose plants, three with undetermined implant fix ation status, and none with fixed implants. A significantly increased accumulation of chronic inflammatory tissues around loose rather than fixed implants suggested a foreign-body reaction as the primary mechan ism of carcinogenesis. A secondary role in carcinogenesis was ascribed to the increased CoCrMo implant SA/BW ratios as indicated by a 14.6% IAT incidence in group 4 versus 3% in group 3. These results support t he notion that early intervention in the removal of loose metal device s is warranted to mitigate against foreign body-induced carcinogenesis , at least in this animal model. (C) 1996 John Wiley & Sons, Inc.