Ion release in patients with metal‐on‐metal hip bearings in total joint replacement: A comparison with metal‐on‐polyethylene bearings

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Abstract
Polyethylene (PE) wear has been shown to be a problem in long‐term joint replacement using metal‐on‐PE bearing. The use of metallic heads articulating with metallic cups could solve this problem: success will be enhanced if wear and corrosion of the articulating surfaces are maintained at a low level. New models with metal‐on‐metal bearing have been proposed, to be used mainly for young subjects: such coupling seems to have a reduced release, but it is unclear yet if the medium‐term corrosion rate is really negligible or, on the contrary, it is significantly higher than in the metal‐on‐PE bearing. Aim of our study was the comparison of ion release in the serum of two groups of patients who had the same type of stable cementless prosthesis, but different bearing: twenty‐six patients with metal‐on‐metal (Group A) and fifteen patients with metal‐on‐PE bearing (Group B) were examined. The follow‐up was 14‐38 months for group A and 18‐34 months for group B. The serum concentration of chromium (Cr), cobalt (Co) and molybdenum (Mo) was measured. Twenty‐two patients before surgery were used for comparison (Group C). The reference values were obtained from a population of twenty‐two healthy subjects (Group D). Our findings indicate that metal‐on‐metal bearings produce a significantly higher systemic release of cobalt and chromium (ng/ml) when compared with levels found in metal‐on‐PE, pre‐surgery and reference groups. Such a high release should induce to improve the bearing materials or, at least, to study the biologic fate of metal ions and consequently their long‐term effects. In such a way a risk‐to‐benefit ratio for the patient could be established. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 467–474, 2002