Metal Particles From Joint Replacements Can Reach the Brain, Study Finds, But Not Linked to Cognitive Change

Researchers from the US and Australia have found evidence that material from a total joint replacement can migrate into brain tissue, adding new information to an ongoing debate about whether the surgery may be linked to Alzheimer's disease risk. Analysing around 700 autopsied brain samples, the team found signs that implant particles can increase the levels of certain proteins associated with Alzheimer's, but found no evidence that this affected brain function.

"For years, we've known that particles can deposit in tissues surrounding the joint, but this is the first study to look at the particles deposited in the brain," said Robin Pourzal, director of Implant Materials Analysis in the Department of Orthopedic Surgery at Rush University in the US. More than 1.5 million people in the US receive a total joint arthroplasty each year, while more than 7 million have Alzheimer's disease; because both conditions are more common in older age, whether their overlap is coincidental has remained an open question.

The researchers used autopsied brain samples from the Rush Memory and Aging Project. Of 885 individuals in the project, 701 brain samples were included in the final metal analysis, including 229 people who had a total shoulder, knee or hip replacement and 472 people with no joint replacement who served as controls. A spectrometric analysis found cobalt concentrations were 8.9% higher across four brain regions in people with a total hip replacement, and electron microscopy confirmed cobalt particles in the samples. Cobalt was linked with a small rise in amyloid-beta protein in the inferior temporal cortex, while titanium was negatively associated with amyloid-beta load. Neither cobalt nor titanium was linked with a change in cognition.

The findings were published in Acta Biomaterialia. Pourzal said total joint arthroplasty "remains one of the most successful and life-changing interventions in modern medicine," but that wear particles from certain hip replacements involving accelerated wear may travel beyond the joint and warrant further study.