Blood Metal Ion Thresholds to Identify Patients with Metal-on-Metal Hip Implants at Risk of Adverse Reactions to Metal Debris

Abstract

Background:The authors of recent studies have reported newly devised implant-specific blood metal ion thresholds to predict adverse reactions to metal debris (ARMD) in patients who have undergone unilateral or bilateral metal-on-metal (MoM) hip arthroplasty. These thresholds were most effective for identifying patients at low risk of ARMD. We investigated whether these newly devised blood metal ion thresholds could effectively identify patients at risk of ARMD after MoM hip arthroplasty in an external cohort of patients.Methods:We performed a validation study involving 803 MoM hip arthroplasties (323 unilateral Birmingham Hip Resurfacing [BHR], 93 bilateral BHR, and 294 unilateral Corail-Pinnacle implants) performed in 710 patients at 3 European centers. All patients underwent whole-blood metal ion sampling, and were divided into 2 groups: those with ARMD (leading to revision or identified on imaging; n = 75) and those without ARMD (n = 635). Previously devised implant-specific blood metal ion thresholds (2.15 μg/L of cobalt for unilateral BHR; 5.5 μg/L for the maximum of either cobalt or chromium for bilateral BHR; and 3.57 μg/L of cobalt for unilateral Corail-Pinnacle implants) were applied to the validation cohort, and receiver operating characteristic curve analysis was used to establish the discriminatory characteristics of each threshold.Results:The area under the curve, sensitivity, specificity, and positive and negative predictive values for the ability of each implant-specific threshold to distinguish between patients with and without ARMD were, respectively, 89.4% (95% confidence interval [CI] = 82.8% to 96.0%), 78.9%, 86.7%, 44.1%, and 96.9% for unilateral BHR; 89.2% (CI = 81.3% to 97.1%), 70.6%, 86.8%, 54.5%, and 93.0% for bilateral BHR; and 76.9% (CI = 63.9% to 90.0%), 65.0%, 85.4%, 24.5%, and 97.1% for unilateral Corail-Pinnacle implants. Using the implant-specific thresholds, we missed 20 patients with ARMD (2.8% of the patients in this series). We missed more patients with ARMD when we used the fixed thresholds proposed by regulatory authorities: 35 (4.9%) when we used the U.K. threshold of 7 μg/L for both cobalt and chromium (p = 0.0003), 21 (3.0%) when we used the U.S. threshold of 3 μg/L for both cobalt and chromium (p = 1.0), and 46 (6.5%) when we used the U.S. threshold of 10 μg/L for both cobalt and chromium (p < 0.0001).Conclusions:This external multicenter validation study confirmed that patients with blood metal ion levels below new implant-specific thresholds have a low risk of ARMD after MoM hip arthroplasty. Using these implant-specific thresholds, we missed fewer patients with ARMD compared with when the thresholds currently proposed by regulatory authorities were used. We therefore recommend using implant-specific blood metal ion thresholds when managing patients who have undergone MoM hip arthroplasty.Level of Evidence:Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

CoCrMo metal release in metal‐on‐highly crosslinked polyethylene hip implants

“…The Co release is complexed by tribocorrosion at the articulating surfaces as well as fretting corrosion at head–neck junction, which explained why no correlation was observed between Ra and Co ion concentration in serum. This observation on different metal ions release between tribocorrosion at articulating surfaces and fretting corrosion at head–neck junction was supported by previous reports on MoM hip system (Garbuz et al, ; Langton et al, ; Matharu et al, ). If the articulating surface was the major releasing source of Cr rather than head–neck junction, Cr/Co is expected to be higher in serum from patients with hip resurfacing (without head–neck junction) than patients with MoM total hip replacement when a large number of samples were compared.…”

“…If the articulating surface was the major releasing source of Cr rather than head–neck junction, Cr/Co is expected to be higher in serum from patients with hip resurfacing (without head–neck junction) than patients with MoM total hip replacement when a large number of samples were compared. One report involving 38 Unilateral Birmingham Hip Resurfacing and 20 Unilateral Corail‐Pinnacle (MoM total hip replacement) cases with adverse tissue reactions showed much higher Cr/Co in blood in hip resurfacing group (0.91) than in total hip replacement group (0.53; Matharu et al, ). Another study revealed 1.73 and 2.15 of mean Cr/Co in serum from total 160 cases of two types of surface resurfacings (Langton et al, ), much higher than 0.67 of mean Cr/Co from 17 patients with MoM total hip replacement (Eltit et al, ).…”

“…Materials loss and metal ions in synovial fluid and serum have been widely studied in MoM hip implants but not in MoP hip implants. Co and Cr ions concentrations in blood/serum have been widely monitored in patients with MoM hip implants (Eltit et al, ; Garbuz, Tanzer, Greidanus, Masri, & Duncan, ; Langton et al, ; Matharu et al, ). Elevated Co and Cr ions were observed in blood of patients with ALTRs associated with wear loss from CoCrMo bearings (Kwon et al, ; McGrory, Payson, & MacKenzie, ).…”

What is appropriate surveillance for metal-on-metal hip arthroplasty patients?

“…The findings from these 2 studies were successfully validated in 710 patients from 3 different European centers (Matharu et al. 2017a ). It was therefore recommended that the newly devised implant-specific blood metal ion thresholds should be used in preference to fixed regulatory authority thresholds when managing MoMHA patients.…”

What’s New in Hip Replacement

“…There remained substantial overlaps between the metal ion levels of well-functioning and poorly functioning metal-onmetal implants 5 . Both lower serum cobalt and chromium thresholds (5 ppb and 2.5 ppb, respectively) 6 as well as implantspecific thresholds 7 were proposed as potential cutoffs for performing metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) with fewer missed cases.…”