Quantitative analysis of the wear and wear debris from low and high carboncontent cobalt chrome alloys used in metal on metal total hip replacements

The biological reactions to polyethylene wear debris have been shown to res ult in osteolysis and loosening of total hip arthroplasties. This has led t o renewed interest in the use of metal on metal bearings in hip prostheses. This study employed uniaxial and biaxial multistation pin on plate recipro cators to assess how the carbon content of the cobalt chrome alloy and the types of motion affected the wear performance of the bearing surfaces and t he morphology of the wear debris generated. The low carbon specimens demonstrated higher wear factors than both the mix ed carbon pairings and the high carbon pairings. The biaxial motion decreas ed the wear rates of all specimens. Plate wear was significantly reduced by the biaxial motion, compared to pin wear. The metal wear particles isolate d were an order of magnitude smaller than polyethylene particles, at 60-90 nm, and consequently, 100-fold more particles were produced per unit volume of wear compared to polyethylene. The low carbon specimens produced signif icantly larger particles than the other material combinations, although it is thought unlikely that the difference would be biologically significant i n vivo. The volumetric wear rates were affected by the carbon content of the cobalt chrome alloy, the material combination used and type of motion applied. Ho wever, particle morphology was not affected by the carbon content of the al loy or the type of motion applied. (C) 1999 Kluwer Academic Publishers.