Release of corrosion products by F-75 cobalt base alloy in the rat. II: Morbidity apparently associated with chromium release in vivo: a 120-day rat study.

There is concern whether in vivo corrosion of chromium-cobalt alloys releases ions containing trivalent [Cr(III)] or hexavalent [Cr(VI)] chromium. The question arises from indications that Cr(VI) is far more biologically active than Cr(III). Using a previously developed microsphere implant model, specimens of F-75 chromium-cobalt-molybdenum alloy were implanted in rats for periods up to 120 days. Blood and urine were collected at intervals during the study. Significant postoperative serum and urine chromium concentration elevations were observed. In addition, weight gain inhibition, lung morbidity, and animal mortality, related to the implant surface area to animal body weight ratio (SA/BW), were observed. Comparison of measured chromium serum concentrations with those concentrations found by others to be biologically active in tissue culture studies strongly suggests the release of Cr(VI) in this study.