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Scientists have discovered that the inflammation in tissue surrounding failing chromium-cobalt metal-on-metal (MOM) implants is caused by the release of cobalt ions (Co²?) from metal debris that wears away from replacement joints. These ions are known to be genotoxic and could lead to further medical complications.

Approximately 10,000 patients in the UK have had cobalt-chromium alloy MOM hip implants, which were recalled in 2010 because rubbing between the components caused nanoscopic metal debris to be released into surrounding tissue, causing chronic inflammation and loss of mobility in patients. To date, 7,500 patients in the UK have had MOM implants removed and replaced with newer implants. However, the mechanism by which the inflammation is caused has not been fully understood.

Now, researchers from Imperial College London and Ohio State University have used a new approach that combines high resolution X-ray and electron microscopy to determine the cause of the chronic inflammation in tissue samples from affected patients. They discovered that residual chromium is oxidised and Co²?ions are released as the nanoparticles corrodes in the tissue, which is the cause of the inflammation. Previous studies have shown that Co²?ions are genotoxic, which could potentially damage DNA and lead to further long-term medical complications in patients.

View a 3D reconstruction ofnanoparticles inside a human white blood cell, developed by the research team. Bright regions in yellow and green show the position of the nanoparticles, which are generated by failing MOM implants. Blue regions are lipid droplets within the cell. The 3D data was acquired using a focussed ion beam/scanning electron microscope.