Correlation Between Co Levels in Hair and Blood of Patients Who Underwent Metal-on-metal Hip Arthroplasty

Abstract

Background: The purpose of this paper is to study the dependence of Co levels in hair on Co levels in blood after metal-on-metal (MoM) hip replacement and prove the suitability of hair analysis coupled to blood analysis in the decision process regarding implant revision evaluation.

Methods: Hair samples of 19 MoM patients having both well-functioning and malfunctioning implants and Co mass concentration levels in blood between 0.2 μg L^-1 and 221.0 μg L^-1 were included. A method based on inductively coupled plasma mass spectrometry was validated and used to measure the Co level in hair.

Results: The Co mass fraction in the hair of patients ranged between 0.011 mg kg^-1 and 0.712 mg kg^-1. A correlation analysis showed a statistically significant positive correlation (r = 0.932, P < .001) between Co in the hair and that in the blood in the full-level range and a statistically nonsignificant positive correlation (r = 0.595, P = .091) in the low-level range.

Conclusions: A correlation between the Co level in the hair and that in the blood exists when the latter is clearly above the 7 μg L^-1 mass concentration threshold suggested for implant revision evaluation. The correlation disappears when the Co level in blood approaches or falls down the mass concentration threshold and that in the hair approaches or falls within the normal population range of 0.004-0.14 mg kg^-1. Accordingly, clinicians could consider a hair analysis coupled to a blood analysis to assess the revision of malfunctioning MoM implants that release metals in patient's body.

Keywords: Cobalt; Hair analysis; Metal-on-metal; MoM hip revision.

Figure 1

Flowchart summarizing the selection of patients included in this study.

Figure 2

Co mass fraction values measured in hair samples of a healthy person (a) and of the ERM-DB001 (b). Gray and black dots represent single and average results, respectively. Error bars, if visible, indicate an expanded uncertainty (k = 2) and refer to the single measurement uncertainty or to the experimental standard deviation in the case of single or average results, respectively. The LTCS average value does not include the LTCS-1 value. INRIM, Istituto Nazionale di Ricerca Metrologica; LTCS, Laboratorio di Tossicologia Clinica e Sperimentale.

Figure 3

Co mass fraction values measured in hair samples (a) and Co concentration values measured in blood samples (b) of the 19 MoM patients. MoM, Metal-on-metal

Figure 4

Hair Co mass fraction, w_Co hair, vs blood Co concentration, c_Co blood, measured in samples of 19 MoM patients, labeled P1-P19. Full-level range (a) and a zoom of the low-level range (b) are shown. The solid straight line is fitted to the P1-P19 data set while the dotted straight line is fitted to the P11-P19 data set. Error bars indicate the expanded uncertainty (k = 2), and arrows point out expected Co level variations in hair according to patient’s history.