In the JournalsPerspective

Blood cobalt levels, device type may predict metal-on-metal hip failure

Elevated concentrations of cobalt in the blood and device type may predict early failure of metal-on-metal hip replacements, according to researchers from the United Kingdom.

“The results suggest that elevated blood meta ion concentrations are associated with early failure of [metal-on-metal] MoM devices secondary to adverse reactions to metal debris,” David J. Langton, MRCS, abd colleagues wrote in a recently published study.

Researchers performed a retrospective analysis of 299 resurfacings in 278 patients who had Articular Surface Replacement ([ASR] DePuy, Leeds, UK) and Birmingham Hip Resurfacing ([BHR] Smith & Nephew, Warwick, UK). The patients reported complications possibly related to metal wear debris and had “slight/occasional pain.” Harris Hip Scores were 95 or greater at the time of venesection. The researchers instituted a blood metal ion screening protocol, ultrasound scanning and joint aspiration to determine the blood cobalt concentration.
Follow up was annual unless symptoms dictated otherwise. Mean postoperative follow-up was 70 months and the mean follow-up post-venesection was 36 months.

Langton and colleagues found blood cobalt concentration and device to be significant risk factors for failure of the hip joint. They found females with high cobalt blood concentration and an ASR device had the highest failure risk. Patients with the BHR device had an 89% reduced risk of revision.

“Cobalt concentrations greater than 20 μg/L are frequently associated with metal staining of tissues and the development of osteolysis,” researchers wrote. “Development of soft tissue damage appears to be more complex with females and patients with ASR devices seemingly more at risk when exposed to equivalent doses of metal debris.” – by Christian Ingram

Disclosure: Langton is an unpaid consultant for Wright Medical and has been reimbursed for individual talks for DePuy and Finsbury. Multiple coauthors are expert witnesses in ongoing litigation regarding MoM hip joints and/or have received reimbursement for travel to educational meetings by Smith & Nephew, Zimmer, DePuy and Wright Medical. One coauthor has received reimbursement for DePuy educational sessions.

Elevated concentrations of cobalt in the blood and device type may predict early failure of metal-on-metal hip replacements, according to researchers from the United Kingdom.

“The results suggest that elevated blood meta ion concentrations are associated with early failure of [metal-on-metal] MoM devices secondary to adverse reactions to metal debris,” David J. Langton, MRCS, abd colleagues wrote in a recently published study.

Researchers performed a retrospective analysis of 299 resurfacings in 278 patients who had Articular Surface Replacement ([ASR] DePuy, Leeds, UK) and Birmingham Hip Resurfacing ([BHR] Smith & Nephew, Warwick, UK). The patients reported complications possibly related to metal wear debris and had “slight/occasional pain.” Harris Hip Scores were 95 or greater at the time of venesection. The researchers instituted a blood metal ion screening protocol, ultrasound scanning and joint aspiration to determine the blood cobalt concentration.
Follow up was annual unless symptoms dictated otherwise. Mean postoperative follow-up was 70 months and the mean follow-up post-venesection was 36 months.

Langton and colleagues found blood cobalt concentration and device to be significant risk factors for failure of the hip joint. They found females with high cobalt blood concentration and an ASR device had the highest failure risk. Patients with the BHR device had an 89% reduced risk of revision.

“Cobalt concentrations greater than 20 μg/L are frequently associated with metal staining of tissues and the development of osteolysis,” researchers wrote. “Development of soft tissue damage appears to be more complex with females and patients with ASR devices seemingly more at risk when exposed to equivalent doses of metal debris.” – by Christian Ingram

Disclosure: Langton is an unpaid consultant for Wright Medical and has been reimbursed for individual talks for DePuy and Finsbury. Multiple coauthors are expert witnesses in ongoing litigation regarding MoM hip joints and/or have received reimbursement for travel to educational meetings by Smith & Nephew, Zimmer, DePuy and Wright Medical. One coauthor has received reimbursement for DePuy educational sessions.

    Perspective

    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 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.

    Perspective

    This is a very interesting study concerning blood metal ion concentrations in asymptomatic patients with metal-on-metal hip resurfacings. One of the two key messages was that male patients with low cobalt concentrations had a very low incidence of adverse tissue reactions and rationalization of resources with regard to follow-up and repeat blood samples in this group may be considered. However, it should be kept in mind that the ion levels are strongly implant design related. This study deals with only two of the many designs. Further, systemic symptoms of cobalt poisoning like neurological disorders and cardiomyopathies may indicate blood cobalt screening, although the hip joint is asymptomatic.

    • Keijo Mäkelä, MD
    • Head of Arthroplasty Unit Turku University Hospital Turku, Finland

    Disclosures: Mäkelä has no relevant financial disclosures.