Metal ion concentrations aftermetal-on-metal hip arthroplastyare not correlated with habitualphysical activity levels

AbstractIntroduction: Metal-on-metal (MoM) hip arthroplasties have shown high clinical failure rates with many patients at riskfor a revision and under surveillance for high metal ion concentrations. Implant wear releasing such ions is assumed to bea function of use, i.e. the patient’s physical activity. This study aimed to assess whether habitual physical activity levels ofMoM patients are correlated with metal ion concentrations and are higher in patients with high (at risk) than in patientswith low (safe) metal ion concentrations.Methods: A cohort study was conducted of patients with any type of MoM hip prosthesis. Metal ion concentrationswere determined using ICP-MS. Habitual physical activity of subjects was measured in daily living using an acceleration-based activity monitor. Outcome consisted of quantitative and qualitative activity parameters.Results: In total, 62 patients were included. Mean age at surgery was 60.8 ± 9.3 years and follow-up was 6.3 ±1.4 years. Cobalt concentrations were highly elevated overall (112.4 ± 137.9 nmol/L) and significantly more in bilateral(184.8 ± 106.5 nmol/L) than in unilateral cases (87.8 ± 139.4 nmol/L). No correlations were found between physicalactivity parameters and metal ion concentrations. Subgroup analysis of patients with low versus high cobalt concentrationshowed no significant differences in habitual physical activity.Discussion: No correlation was found between physical activity levels and metal ion concentrations. Implant use bynormal habitual activities of daily living seems not to influence metal ion concentrations.