Hip and knee replacements: even when they work well, they ‘age’ inside the body
In fact, from the very day after orthopaedic surgery, hip and knee prostheses engage in a sort of chemical and mechanical war with the body that hosts them – a war that never ends
Key points
When you look at it before implantation, a hip or knee prosthesis appears to be an inert piece of metal which, as such, might remain unchanged for decades inside the body. But this is not the case. In fact, from the very day after orthopaedic surgery, hip and knee prostheses engage in a sort of chemical and mechanical battle with the body that hosts them – a battle that never stops, not even for a moment, not even at night.
This leads to a series of consequences that contribute to the wear and tear of the prosthesis and which, at a certain point, make a repeat operation necessary. But what are the processes that contribute most to the ageing of orthopaedic prostheses? This was the question posed by a study published in npj Materials Degradation (part of the Nature group), conducted by Western University and the London Health Sciences Centre Research Institute (LHSCRI) in Canada, which analysed over 240 hip and knee prosthetic components removed from patients during revision surgery.
The culprit is ‘tribocorrosion’
The laboratory where the study was conducted, headed by Matthew Teeter, a professor at the Schulich School of Medicine & Dentistry, houses Canada’s largest collection of hip, knee, shoulder and dental prostheses removed following failure.
A veritable living archive of the biomechanics of the human body, which researchers cross-reference with similar data collection networks operating in Australia, the United States and Slovenia. “Having a prosthesis in your body literally changes your body’s chemistry,” explains Yolanda Hedberg, professor of chemistry at Western University. “You may not feel any pain or other symptoms, but your body’s chemistry is constantly changing.”
The main culprit behind this damage has a rather ominous technical name: it is tribocorrosion (‘tribology’ is the study of friction, wear and lubrication), which occurs when movement and chemical reactions act upon the same surface at the same time, thereby multiplying the damage compared to what either would cause on its own.
