 Background: Chronic systemic exposure to very high concentrations of cobalt or chromium following large diameter metal-on-metal hip resurfacing or hip replacement MOMHR associates with cardiac, thyroid, visual, hearing, and peripheral neurological deficits. Chronic exposure to lower circulating metal levels also associates with changes in cardiac function and bone metabolism in case-control analyses. However, it remains unclear what the risk of these problems is in the general population exposed to MOMHR. 