New findings by a team of researchers from the US and Australia have complicated an ongoing debate over whether a total joint arthroplasty may increase the risk of Alzheimer’s disease.
Although their analysis of around 700 autopsied brain samples found strong evidence that material from a joint replacement can migrate into neurological tissue and increase the load of proteins associated with the disease, the scientists found no evidence that it impacted brain function.
This is good news for anybody who has implants or is in the process of receiving one. However, the researchers argue that the potential for small bits of metallic debris to impact cognitive health can’t be ruled out.
“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,” says Robin Pourzal, the Director of Implant Materials Analysis in the Department of Orthopedic Surgery at Rush University in the US.
More than 1.5 million patients living with osteoarthritis in the US receive a total joint arthroplasty each year. Meanwhile, more than 7 million individuals have Alzheimer’s disease. Given that both conditions affect the elderly more than any other demographic, it’s unsurprising to find a significant overlap between them.
Whether this relationship is purely due to age has long remained an open question.
In theory, sub-micron-sized particles scoured from the implant’s surface by years of wear and tear could embed themselves in the brain, increasing the chances of neurodegeneration. After all, debris from implants is known to trigger local immune responses and even be detectable in the blood and other organs.
To determine whether implants containing an alloy of cobalt-chromium-molybdenum and titanium-aluminum-vanadium could cross the blood-brain barrier, researchers collected autopsied samples from deceased volunteers in the Rush Memory and Aging Project.
Of the 885 individuals, 701 brain samples were included in the final metal analysis, and 229 volunteers had a total shoulder, knee, or hip replacement. A further 472 had no joint replacement, so served as controls.
A spectrometric analysis found an association between cobalt concentrations across four regions of the brain and total hip arthroplasties, with tissue samples 8.9% higher in individuals with an implant. Electron microscopy also revealed cobalt particles in the samples.
Curiously, cobalt was linked with a small rise in amyloid-beta proteins in the inferior temporal cortex. Titanium, on the other hand, was negatively associated with amyloid-beta load.
Crucially, the presence of either cobalt or titanium wasn't linked with a change in cognition.
The study affirms the safety of joint replacements, which give millions around the world a new lease on life each year.
“Total joint arthroplasty remains one of the most successful and life-changing interventions in modern medicine,” says Pourzal. “But it does suggest that wear particles from the implant, particularly in certain hip replacements involving accelerated wear, may travel beyond the joint and warrant further study.”
This research was published in Acta Biomaterialia.
Source: Rush University.
