Tissue reactions and sensitivity to iron-chromium alloys

The aim of the study is to see whether corrosion of metallic implants in a living body is related to metal sensitivity reactions. As model materials, we prepared iron (Fe)-chromium (Cr) binary alloys containing various amounts of Cr, having different corrosion resistance. As a comparison, 316L type stainless steel (SUS316L) was used. These specimens were subcutaneously implanted into rats, and the tissue reactions around the implants and the sensitivity to Cr were evaluated by histological examination, patch testing and lymphocyte proliferation tests. After 4 months implantation, there was rust on the surface of all 10%Cr-Fe alloys, three 15%Cr-Fe alloys and one 20%Cr-Fe alloys out of 4 specimens per each group. There were no significant toxicological sign in any of the animals. Tissue responses, such as extent of hemorrhage and frequency of inflammatory cells in or around the fibrous capsule, were scored and the sum total score was determined. With regard to total score of tissue response, no significant difference was found among the groups. Concerning the thickness of fibrous capsule, 10% and 20%Cr-Fe alloy group was somewhat higher than other Cr-Fe alloys and SUS316L, but there was not significant difference. In the histological examination of tissue responses, the sign of metal sensitivity could not be obtained. Although there was no significant difference in the lymphocyte proliferation activity by addition of potassium dichromate (K2Cr2O7)-solution among the implanted groups, two animals exhibited positive skin reactions by topical challenge with K2Cr2O7 in 10%Cr-Fe alloy-implanted group. In 15% and 20%Cr-Fe alloy groups, each one showed a skin response. The skin reaction observed was mainly edema that is characteristic of metal allergy. This suggests that some animals were sensitized to Cr by the implantation of easily corroded Cr-Fe alloy, and the corrosion products of metallic devices in body fluid is likely responsible for development of metal hypersensitivity.