Erroneous aluminum and cobalt tissue concentrations from using formalin.

Because of the liberation of metal particles from orthopedic implants, concerns have been voiced about their long-term safety. To document the presence and measure the amount of metal in periprosthetic tissues, many reports have analyzed tissue specimens obtained from revision surgery. Some report the inclusion of formalin in tissue processing. However, the unavailability of any medical-grade formalin solution with a known metal content raises the suspicion of sample contamination. The purpose of this study was to measure the concentration of the metals in the formalin found in common orthopedic alloys and to assess this chemical's role in removing metal ions from tissue samples. To do this, tissues with known metal concentrations of cobalt and aluminum were mixed with formalin, and the differences in the formalin and tissue concentrations of these elements were evaluated. Tissue and formalin samples were tested prior to and immediately after their mixing and then at three 10-day intervals. At the end of the study additional unmixed samples of formalin and tissue for both metals were tested to ensure there had been no contamination. Both cobalt and aluminum were found in off-the-shelf formalin, with observed decreases in tissue metal concentration and increases in formalin metal concentration.