Metal-on-metal bearings in total hip arthroplasties: Influence of cobalt and chromium ions on bacterial growth and biofilm formation.

Metal-on-metal (MOM) bearings involving cobalt-chromium (Co-Cr) alloys in total hip arthroplasties are becoming more and more popular due to their low wear. Consequences of corrosion products of Co-Cr alloys are for the most part unclear, and the influence of cobalt and chromium ions on biofilm formation has never been studied. Therefore, the aim of this study was to evaluate how Co-Cr ions affect bacterial growth, biofilm formation, and architecture. A collection of clinically isolated and commercially available bacterial strains were exposed to Co-Cr concentrations as found in serum and above as found in adjacent tissue. Planktonic growth of bacteria was inhibited by concentrations of 200,000/93,000 microg/L Co-Cr. Co-Cr concentrations up to 20/9.3 microg/L as reported to occur in serum revealed no consistent influence on biofilm formation, but higher concentrations of 200,000/93,000 microg/L significantly reduced Staphylococcus aureus and CNS biofilm formation. As indicated by confocal laser scanning microscopy, no dead bacteria were encountered in the biofilms, and the metal ion concentrations used must be classified as growth-inhibiting and not bactericidal. Long-term clinical data on infection rates for Co-Cr MOM-bearings are not yet available, but the current results suggest that Co-Cr ions may yield these prostheses less prone to biofilm formation and subsequent infection.