Researchers at UCD have found that when it comes to knee-joint replacements, the current 'one size fits all' approach is seriously flawed, writes Claire O'Connell
Nature seldom offers a one-shape-fits-all option. And Irish engineers are discovering that knee joints are no exception.
A team at University College Dublin has taken the first comprehensive look at how multiple factors such as gender, ethnicity and disease affect knee shape. Their findings suggest that more options should be available to surgeons performing knee replacements.
"The basic design for total knee replacement goes back to the 1970s, and much of the original sizing and geometry dates from then," says Dr David FitzPatrick, head of UCD's head of the school of electrical, electronic and mechanical engineering. Most knee-shape studies to date have looked at Caucasian joints and have zoned in on differences between male and female knees, he adds.
But the UCD team wanted to take things a step further and look at the combined effects of multiple factors on knee shape. Those factors included gender, ethnicity, osteoarthritis and natural variability, explains Dr Niall Rooney, who completed his doctorate on the knee project and is now working in Sydney, Australia.
To compare factors, the team sourced around 200 CT scans of knees from patients in Japan, Europe and the United States. The three-dimensional nature of the scans allowed the researchers to build up a computer model of the knee joint, explains Dr Rooney.
"An X-ray gives a two-dimensional sheet approximating the geometry of the knee, whereas a CT scan is like a series of X-ray sheets overlaid in the third dimension," he says. "So you have a proper, three- dimensional view of the whole knee."
Rooney's focus was on the top bone in the knee joint, which is the lower end of the thigh bone. This is the least forgiving bone in a knee replacement, and choosing a suitable shaped implant is crucial to the operation's long-term success, according to the researchers.
At the moment, artificial knees for implant come in a range of standard sizes with little variation in shape. But the scans from patients show huge variability in knee shape across different size, gender, ethnic and disease groups, says Dr Rooney.
"Suppose you have a Caucasian female and a Japanese male of the same knee size; their knee shapes may differ to the extent that they warrant totally different shaped implants," he says.
The range of knee shapes that cropped up in the scans suggests that surgeons should have more options for choosing the most fitting knee implant for a particular patient, says Dr FitzPatrick.
"The challenge for the designer isn't to design for a Japanese knee or a Caucasian knee, or a male knee or a female knee, the challenge is to design for the diversity within the population, which is huge," he states.
The research group, which is funded by Enterprise Ireland and orthopaedic implant manufacturers DePuy, is currently looking at other bones within the knee, and their approach of building anatomical simulations from CT scans could also be applied elsewhere, says Dr FitzPatrick.
"The techniques we have developed we can apply to any joint in the body and I think it's something we will probably move into in the future."