Metal-on-metal arthroplasty, cobalt toxicity, and development of cognitive impairment: a systematic review

Neurological dysfunction secondary to cobalt toxicity has been described as a potential complication of metal on metal (MoM) arthroplasty, however, to date the full extent of this association remains unclear. Currently, no national guideline on the management or follow-up of MoM arthroplasty patients recommends monitoring for potential insidious cognitive decline or long term consequences. The aim of this study was to summarise the available evidence regarding the relationship between MoM arthroplasty associated cobalt toxicity and cognitive impairment (CI).

A systematic review of literature describing cobalt concentrations associated with neurocognitive symptoms in patients with MoM implants was undertaken. The study was registered with PROSPERO on the 18th July 2023 (CRD42023436880), in concordance with PRISMA guidelines. The Downs and Black Checklist assessed the risk of bias and evidence quality. Primary outcomes were reports of CI and blood cobalt concentration at presentation and following revision surgery.

Of 361 records identified, 15 relevant publications were included. Downs and Black Checklist assessment revealed that few high-quality studies currently exist. A clear association between MoM arthroplasty and CI, across varied follow up periods, was described by all 15 studies. Mean serum cobalt concentrations at presentation of CI were 9.75ug- 625ug, however no threshold cobalt concentration was identified. Over 85% of papers which recorded post-revision outcomes reported partial, if not complete, resolution of pre-operative CI following revision surgery.

This study provides the first robust systematic examination of the evidence surrounding metal on metal arthroplasty, cobalt toxicity, and potential CI. While further research is required to evaluate the exact nature of this relationship, our findings suggest that national and international guidelines should highlight the possible cognitive dysfunction secondary to MoM arthroplasty associated cobalt toxicity, including the need for routine assessment of cognitive function in those who received MoM implants.