This paper examines the association between elevated blood metal ion concentrations and early failure of hip resurfacing devices due to local adverse reaction to metal debris in asymptomatic patients. It provides the first evidence that blood metal ion tests can be used as a clinical indicator of the risk of early joint failure in asymptomatic patients. The main weakness of the paper was the lack of standardization of the time at which blood samples were taken postoperatively and the short minimum postoperative follow-up of the patients with a widespread range of 12 months to 118 months. To analyze the effect of this variation in time from primary surgery to sampling, a generalized linear mixed effect model was constructed.
In a recent study, we evaluated the clinical and radiographic long-term results as well as the serum metal concentrations of a series of 105 cementless total hip arthroplasties with a 28-mm high-carbon metal-on-metal bearing (Metasul, Zimmer GmbH; Winterthur, Switzerland) in 98 patients with an average age of 56 years, after a minimum of 17 years follow-up 1. In this study, to our knowledge the longest follow-up of that kind of implant, we found no significant or consistent correlation between the mean postoperative serum ion levels and the mean values of age, gender, body mass index, Harris Hip Score and UCLA activity score based on the present sample size. This is in agreement with results of several studies showing that metal ion levels are not acutely affected by patient activity. At the American Academy of Orthopaedic Surgeons Annual Meeting in 2013, the Hip Society declared systemic ion levels are just one factor in the evaluation and should not be relied upon solely to determine the need for revision surgery. Furthermore, there are many complex issues associated with the analysis of metal ions, including collection technique, analysis and reporting of the results.
This is in contrast to this study by Langton and colleagues who found a positive and significant risk factor of elevated blood metal ion concentrations, gender and the type of device for joint failure in asymptomatic patients with metal-on-metal hip resurfacings. The results of this study have important clinical implications and should be investigated in further evaluations in the medium to long term.
Richard Lass, MD
Department of Orthopedics, Medical University of Vienna
Disclosures: The author did not receive grants or outside funding in support of their research on this topic and did not receive payments or other benefits from a commercial entity (Zimmer GmbH; Winterthur, Switzerland). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or non-profit organization with which the author is affiliated.