Follow-Up of Metal-on-Metal Hip Arthroplasty Patients Is Currently Not Evidence Based or Cost Effective
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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2021, Journal of ArthroplastyCitation Excerpt :Current MHRA guidance of in situ MoM THRs does not stratify high-risk patients according to component specifications or patient demographics. Furthermore, patients with failing MoM THRs often present asymptomatically, thus implementation of non-specific decision algorithms to identify those at risk will have costly implications on clinical and investigatory resources [26–28]. Our study has highlighted component parameters at increased risk of revision, and this will allow for formulation of optimal evidence-based and cost-effective follow-up guidance that stratifies for high-risk patient groups.
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.