Hip Replacement Wear And Tear

Nanoparticulate debris generated when the pieces of cobalt-chromium alloy metal-on-metal hip replacements rub together has been fingered as the cause of premature failure of those devices. But precisely what metal species are getting into the tissues around these implants and causing inflammation has been something of a mystery. A team led by Alexandra E. Porter and Mary P. Ryan of Imperial College London and David W. McComb of Ohio State University has now used X-ray absorption spectroscopy and electron energy loss spectroscopy to characterize the nature of these breakdown products for the first time (Chem. Commun., DOI: 10.1039/c2cc33016d). The researchers examined tissue taken from around a failed implant and found the metal-wear products in two distinct chemical states in macrophages—the cells whose job it is to clean up debris. They noted a small amount of metallic cobalt and chromium nanoparticles, but the majority of what they observed was Cr³⁺ ions. What they didn’t see much of was cobalt, suggesting that much of that element had been released into the bloodstream as Co²⁺, which is known to be genotoxic. They believe cobalt ions are the likely culprits behind the inflammatory response.