Elsevier

The Journal of Arthroplasty

Volume 30, Issue 8, August 2015, Pages 1317-1323
The Journal of Arthroplasty

Follow-Up of Metal-on-Metal Hip Arthroplasty Patients Is Currently Not Evidence Based or Cost Effective

https://doi.org/10.1016/j.arth.2015.03.009Get rights and content

Abstract

Over one-million patients worldwide have received metal-on-metal (MoM) hip arthroplasties with a significant proportion requiring revision surgery in the short-term for adverse reaction to metal debris (ARMD). Worldwide authorities have subsequently issued follow-up guidance for MoM hip patients. This article compares follow-up guidelines for MoM hips published by five worldwide authorities, analyses these protocols in relation to published evidence, and assesses the financial implications of these guidelines. A number of major differences exist between authorities regarding patient follow-up, with vast cost differences between protocols (£84 to £988/patient/year for stemmed MoM hips and £0 to £988/patient/year for hip resurfacing). Current worldwide guidance is neither evidence-based nor financially sustainable with most protocols lacking the sensitivity to detect asymptomatic ARMD lesions.

Section snippets

Follow-Up Guidelines

Guidance for MoM hip follow-up has been issued by the: UK Medical and Healthcare Products Regulatory Agency (MHRA) [16], European Federation of National Associations of Orthopaedics and Traumatology (EFORT) [17], United States of America (USA) Food and Drug Administration (FDA) [18], Therapeutic Goods Administration of Australia [19], and Health Canada [20] (Table 1). Major differences in follow-up guidance exist between authorities.

Do All Patients Require Follow-Up?

All MoM hips are theoretically at risk of ARMD. It is clear that implants with high failure rates need regular follow-up. These include all large-diameter MoM THAs given their significantly higher failure rates compared to other articulations [5]. Follow-up for HR patients is less clear.

Similar follow-up protocols for THAs should be used for HR designs with poor outcomes, with MHRA guidance reflecting this for the Articular Surface Replacement (ASR) HR. The Birmingham Hip Resurfacing (BHR) is

Should Symptoms Decide Follow-Up?

Although all authorities stratify follow-up according to symptoms, asymptomatic ARMD lesions have been observed in up to 61% of MoM hips 29., 30., 31.. This approach will result in ARMD being undetected in asymptomatic patients. In particular, FDA and Canada allocate limited resources for asymptomatic THA patients who are known to be at risk of implant failure (6.2% five-year failure rate for MoM THAs compared to 1.6% for other articulations) [5].

Role of Blood Metal Ions

Blood metal ions are a surrogate marker of in-vivo MoM bearing wear [32]. Some studies have demonstrated that raised blood metal ion concentrations are associated with MoM hip failure 33., 34., 35., 36..

Although both whole blood and serum metal ions are acceptable investigations, important differences exist between sample types. Serum cobalt and chromium are up to 1.4 times greater than their respective values in whole blood, with stronger correlation of cobalt in serum and whole blood compared

Role of Cross-Sectional Imaging

Numerous studies have demonstrated that both ultrasound and MARS MRI are acceptable for identifying ARMD in MoM hips 29., 30., 43., 45., 46., 47.. All authorities recommend using either modality with no preference stated. These recommendations are appropriate as presently no consensus exists regarding which modality is most effective for identifying ARMD or monitoring progression [48], with the relative merits of each previously described [49].

Few studies have compared ultrasound against MARS

When Should Follow-Up Be Repeated?

Decisions regarding follow-up regularity require well-designed longitudinal cohort studies with patients undergoing repeated assessments. Although the natural history of ARMD remains incompletely understood [56], more recent studies have assessed the utility of repeating blood metal ions and cross-sectional imaging in MoM hips.

What Is the Threshold for Revision?

Poor short-term outcomes have been reported following ARMD revision 10., 11. with few studies assessing prognostic factors of outcomes post-revision 53., 63., 64.. One study attributed improved outcomes following ARMD revision to increased experience and earlier surgery [63]. As the threshold for revision has not yet been determined, all authorities recommend revision in patients with imaging abnormalities, especially if progressing, and rising blood metal ions. This appears reasonable until

Financial Analysis of Guidelines

Using MoM hip follow-up guidance from worldwide authorities (Table 1) a financial analysis was performed for common clinical scenarios (Table 2). HR patients with high-risk devices and/or ARMD risk factors were not considered separately because follow-up regimens, and therefore costs, generally parallel those for large-diameter THAs (Table 2: Scenario 1). Follow-up costs have been described previously [65]. The total cost for each scenario represents the annual follow-up of one patient.

Discussion

Serious concerns were raised regarding patient safety when high failure rates of some MoM hips were publicised 3., 8., 66., 67.. Medico-legal pressures have compounded the problem leading to worldwide authorities issuing guidance based on available evidence. Generally follow-up guidance was conservative to reflect these concerns, but also because ARMD was not well understood. Although our understanding of ARMD has since improved, it remains incomplete. This article provides a novel insight into

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    The authors would like to thank The Royal College of Surgeons of England and The Arthritis Research Trust, which have provided one of the authors with funding in the form of a Surgical Research Fellowship.

    One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.03.009.

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