Advantages and limits of determinating serum cobalt levels in patients with metal on metal articulating surfaces

Purpose of the study The purpose of this study was to measure the serum cobalt levels and their correlation with clinical and radiological findings in patients with metal on metal hip articulating surfaces. Method Forty-one patients with metal on metal hip arthroplasty were reviewed retro spectively at mean follow-up of 12.9 months. Serum cobalt levels were deter mined for each patient by atomic absorption spectrometry at the maximal fol low-up and were compared to a control group (19 patients). Two patients and one control subject also performed exercise on a treadmill in order to app reciate the influence of physical activity on serum cobalt levels. Results The metal on metal group presented higher serum cobalt levels than those of the control group (p < 0.0001). There was no correlation between serum cob alt and clinical and radiological findings at the exception of patient age (n = 40, r = 0.37). However, when the follow-up was greater than 18 months, mean serum cobalt was significantly higher compared to a follow-up less th an 18 months. The physical exercise test led to a moderate elevation (aroun d 10 p. 100) of cobalt in the two patients but not in the control subject. Discussion and conclusion The interpretation of an elevated cobalt serum level is difficult. Cobalt-c ontaining drugs, other implants, excess of activity and diseases (renal fai lure) may influence serum cobalt level. In this study, the high serum cobal t levels seem not linked to a failure of the implant, mainly because of the short follow-up. They could rather be attributed to an increase of the pat ient activity beginning 18 months after the surgery. Because potential long-term cobalt toxicity and carcinogenicity is not well known, careful medical follow-up should be emphasized specially in young p atients.