The effectiveness of blood metal ions in identifying bilateral metal-on-metal total hip arthroplasty patients at risk of adverse reactions to metal debris

Abstract

We investigated whether blood metal ions could effectively identify bilateral metal-on-metal total hip arthroplasty (THA) patients at risk of adverse reactions to metal debris (ARMD).

Whole blood metal ions were sampled in 50 patients with bilateral 36mm Corail-Pinnacle THAs. Patients were divided into ARMD (n=10) and non- ARMD groups (n=40), with optimal ion thresholds for identifying ARMD determined using receiver operating characteristic analysis.

Maximum cobalt or chromium produced the highest area under the curve (71.8%). The optimal ion threshold for distinguishing between patients with and without ARMD was 4.0μg/l (90.0%=sensitivity, 65.0%=specificity, 39.1%=positive predictive value, 96.3%=negative predictive value). Fixed regulatory authority thresholds missed more patients with ARMD (10%-12% missed) compared to our threshold (2% missed).

Bilateral THA patients with blood metal ions below our threshold were at low-risk of ARMD. Compared to currently recommended fixed authority thresholds, our threshold appears preferable for managing patients with these particular implants.