Association between systemic inflammation and serum cobalt level in patients with metallic implants: Evidence from...

The long-term implantation of metallic prostheses in orthopedic surgery, particularly cobalt-chromium-molybdenum (CoCrMo) alloys, raises growing concerns about metal ion release and associated inflammatory responses. Although mechanical wear and corrosion are established contributors to cobalt ion exposure, emerging evidence suggests that host inflammatory status may also be linked to ion release. The Inflammatory Burden Index (IBI), integrating C-reactive protein and neutrophil-to-lymphocyte ratio (NLR), offers a comprehensive marker of systemic inflammation. This study aimed to investigate the association between IBI and serum cobalt as well as chromium levels in individuals with intracorporeal metallic implants.

We conducted a cross-sectional analysis using data from the National Health and Nutrition Examination Survey (NHANES) from 2015 to 2020. A total of 668 participants were enrolled after excluding individuals without relevant metal exposure or with incomplete data. Serum cobalt and chromium levels, IBI calculated as CRP (mg/L) × NLR, and relevant covariates were analyzed. Survey-weighted linear regression models were used to examine the association between IBI and serum cobalt, with subgroup analyses stratified by gender and age. Statistical analyses were conducted using R and EmpowerStats.

Participants with high IBI had significantly higher serum cobalt levels, but chromium levels did not differ between the groups. Multivariate linear regression analyses revealed a positive correlation between IBI and serum cobalt levels, with the association being particularly pronounced in males and individuals aged 50-70 years. In the fully adjusted model, serum cobalt levels were 9.978 nmol/L higher in participants in the highest IBI tertile compared to those in the lowest tertile (P < 0.001). Subgroup analyses further confirmed that this association remained significant among males (β = 0.413, 95 % CI: 0.293-0.532) and participants aged 50-70 years (β = 0.332, 95 % CI: 0.036-0.627).

This study reveals a positive association between IBI levels and serum cobalt-but not chromium-in individuals with intracorporeal metallic implants, with particularly strong associations in men and older adults. These cross-sectional findings suggest a close link between host inflammatory status and cobalt exposure, although causality and directionality cannot be determined. Composite inflammatory indices such as the IBI may help identify patients at higher risk of cobalt elevation, a possibility that should be tested in prospective studies.