To find out if there is an inverse association between estimated glomerular filtration rate (eGFR) and whole blood cobalt (Co) and chromium (Cr) levels in patients with metal-on-metal (MoM) hip arthroplasties and renal insufficiency, suggesting that renal insufficiency could cause accumulation of Co and Cr in blood. Out of 2,520 patients with 3,013 MoM hip arthroplasties, we identified 1,244 patients with whole blood Co, Cr, and creatinine measured within no more than a one-year interval. We analyzed the correlation of blood metal ion levels and eGFR to identify a potential trend of accumulating Co or Cr with decreasing eGFR.Aims
Methods
To determine whether there is any association between glomerular
filtration rate (GFR) and blood cobalt (Co) and chromium (Cr) levels
in patients with metal-on-metal (MoM) hip arthroplasty. We identified 179 patients with a unilateral 36 mm diameter head
as part of a stemmed Summit-Pinnacle MoM hip arthroplasty. GFR was
calculated using the Modification of Diet in Renal Disease formula.Aims
Patients and Methods
Recent studies have demonstrated that implant-specific blood metal ion thresholds exist in unilateral and bilateral metal-on-metal (MoM) hip arthroplasty patients, with these thresholds being most effective for identifying patients at low-risk of adverse reactions to metal debris (ARMD). We investigated whether these new blood metal ion thresholds could effectively identify patients at risk of ARMD in an external cohort of MoM hip arthroplasty patients. We performed a validation study involving 803 MoM hip arthroplasties implanted in 710 patients at three European centres (323=unilateral Birmingham Hip Resurfacing (BHR); 93=bilateral BHR; 294=unilateral Corail-Pinnacle). All patients underwent whole blood metal ion sampling. Patients were divided into those with ARMD (revised for ARMD or ARMD on imaging; n=75), and those without ARMD (n=635). Previously devised implant-specific blood metal ion thresholds (cobalt=2.15μg/l for unilateral BHR; maximum cobalt or chromium=5.5μg/l for bilateral BHR; cobalt=3.57μg/l for unilateral Corail-Pinnacle) were applied to the validation cohort, with receiver operating characteristic curve analysis used to establish the discriminatory characteristics for each respective threshold. The area under the curve, sensitivity, specificity, positive predictive value and negative predictive value for distinguishing between patients with and without ARMD for each implant-specific threshold were respectively: unilateral BHR=89.4% (95% CI=82.8%-96.0%), 78.9%, 86.7%, 44.1%, 96.9%; bilateral BHR=89.2% (95% CI=81.3%-97.1%), 70.6%, 86.8%, 54.5%, 93.0%; unilateral Corail-Pinnacle=76.9% (95% CI=63.9%-90.0%), 65.0%, 85.4%, 24.5%, 97.1%. The 7μg/l UK MHRA threshold missed significantly more patients with ARMD compared with the implant-specific thresholds (4.9% vs. 2.8%; p=0.0003). This external multi-centre validation study has confirmed that MoM hip arthroplasty patients with blood metal ion levels below newly devised implant-specific thresholds have a low-risk of ARMD. Compared to implant-specific thresholds, the currently proposed fixed MHRA threshold missed more patients with ARMD. We recommend using implant-specific thresholds over fixed thresholds when managing MoM hip arthroplasty patients.
We conducted a retrospective study to assess
the prevalence of adverse reactions to metal debris (ARMD) in patients
operated on at our institution with metal-on-metal (MoM) total hip
replacements with 36 mm heads using a Pinnacle acetabular shell.
A total of 326 patients (150 males, 175 hips; 176 females, 203 hips)
with a mean age of 62.7 years (28 to 85) and mean follow-up of 7.5
years (0.1 to 10.8) participating in our in-depth modern MoM follow-up
programme were included in the study, which involved recording whole
blood cobalt and chromium ion measurements, Oxford hip scores (OHS)
and plain radiographs of the hip and targeted cross-sectional imaging. Elevated
blood metal ion levels (>
5 parts per billion) were seen in 32 (16.1%)
of the 199 patients who underwent unilateral replacement. At 23
months after the start of our modern MoM follow-up programme, 29
new cases of ARMD had been revealed. Hence, the nine-year survival
of this cohort declined from 96% (95% CI 95 to 98) with the old
surveillance routine to 86% (95% CI 82 to 90) following the new
protocol. Although ARMD may not be as common in 36 mm MoM THRs as
in those with larger heads, these results support the Medicines
and Healthcare Products Regulatory Agency guidelines on regular
reviews and further investigations, and emphasise the need for specific
a follow-up programme for patients with MoM THRs. Cite this article:
