Cobalt determination in the hair of patients after metal-on-metal hip implants by instrumental neutron activation analysis

Recently, following an alert regarding possible problems of toxicity issued by national medicine authorities, thousands of patients with hip implants have been recalled for a set of analysis, including cobalt determinations in blood and urine. Within this framework, additional measurements of cobalt levels in hair are recommended to monitor the release of metals in the body after surgery. Aiming at a clinical application, the standardization of the hair washing protocol used to remove possible external contamination is essential. To this aim, a method suggested by the International Atomic Energy Agency (IAEA) and based on repeated washings with acetone and deionized water was tested. Specifically, hair samples of two healthy subjects and three patients were measured at different steps of the washing sequence to observe the decrease in the level of cobalt to the plateau corresponding to the bound component. The data confirmed the suitability of the washing method and proved high levels of bound cobalt in the hair of two patients requiring revision hip surgery. Moreover, the cobalt bound component was not affected by the neutron exposure of hair. As a result, the use of instrumental neutron activation analysis might be advantageous compared to other analytical techniques.