Touching Lives - March 2004
Walking back to happiness
When Mark Taylor’s mother was advised to have a knee replacement operation, she knew just who to turn to for advice. Unlike most of us, she has a leading expert on knee replacement in the family!
“I just gave simple advice really,” says Mark. “If I was having a knee replacement I’d want to go to a surgeon who was doing a reasonable number of operations each year. If one surgeon was doing five a year, and another 50, I’d go to the guy doing 50!”
Mark has been advancing our understanding of knee replacement and prostheses for much of his working life. Graduating from university in 1991 with a degree in Mechanical Engineering, it was his Master’s degree in Bioengineering that crucially led Mark to get interested in the application of engineering to the human body.
And, whilst completing his PhD thesis in London, Mark first came into contact with Action Medical Research — for 18 months of his study he was employed as a research worker on a project funded by the Charity to investigate stresses on the bone after knee replacement surgery. Now things have come full circle and Mark is lead grantholder for a brand new project which aims to shed further light on this common medical procedure.
30,000 knee replacement operations take place in the UK every year, making it almost as common a procedure as hip replacement. When you add worldwide demand to this figure — 266,000 knee replacement operations are performed in the United States each year — you can see clearly the importance of perfecting both surgical technique and design of implant. Ageing populations in richer nations means there will be no let up in demand for the surgery in coming years.
An independent project
Based at the School of Engineering Sciences in the University of Southampton, the three-year Action Medical Research project began in September 2003 with a grant of £83,000.
“^We were delighted to receive our grant from Action Medical Research, It means a lot to have funding from such an independent source. It is often difficult to get funding from orthopaedic companies for fundamental research,^ as they are often interested in advancing a particular design concept. Not being tied to looking at a specific implant’s design means we can go right back to basics, and hopefully get the best possible outcome.”
Incredibly there are some 30-40 different designs of knee implant on the market in the UK, with significant differences between designs. Mark explains, “One thing we are concerned to do is assess these differences in design. Manufacturers will do fatigue tests on implants — they might apply a load to a knee implant and put it through a machine for up to five million cycles to see if it breaks.
“But the human body is much more complex than that, and how the implant operates when it’s actually inside the body can make all the difference to its longevity. We use highly sophisticated computer models to simulate the body’s interaction with the implant.”
The success or otherwise of this project lies in the development of new testing models for knee implants, Mark says. “We want to use computers to simulate the effects of somebody walking and performing other daily activities, so we can evaluate the stresses on the bone within the knee.
“Part of this project will then look at the design of the implant and reach conclusions on what is best — for example, would you want to use a two pegs, keel or stem design to maximise the fixation of the implant to the bone? But just as important to outcomes we think is surgical technique.
“Surgeons are human beings, and as such they can never be 100 per cent accurate. As an engineer I know that in manufacturing you expect accuracy to be within a few tenths or hundredths of a millimetre. But the reality of surgery means that when the surgeon puts the prosthesis in, accuracy may vary by as much as two or three whole millimetres!”
The surgeon’s skill
Factors such as the surgeon’s level of skill and their performance on the day can have a significant impact on the long-term success of the operation. So Mark and his team’s computer model will assess what impact poor alignment of the prosthesis can have on performance.
“We need to see what effect differences in position have on performance and function of knee implants — physically how the implant moves within the body, and the stresses poor alignment will generate within the shinbone. If you take two of these 30-odd designs on the market, one may be insensitive to these variabilities in the surgeon’s style, the other might be very sensitive.
“Our aim is to push forward the methods available to assess implant performance, which in turn should help to generate knee designs which can work well with all different surgical styles. What we discover should also help surgeons to refine and improve their techniques.”
Inspiration and perspiration
Mark is deeply committed to pushing back the boundaries of our knowledge of knee replacement. And this, he says, is usually achieved through sheer hard work. “I admit I can get wrapped up in the scientific challenge of my work. That’s what attracts me to the profession after all — there are too many unanswered questions! So I sit in on surgery a couple of times a year to refresh myself as to the reality of surgery and the practicalities facing the surgeon.
“^As an engineer I can’t afford to forget that this is all about patients undergoing surgery at the end of the day^. But it’s precisely because our team does work in a School of Engineering Sciences — alongside aerospace and automotive engineers — that we can achieve so much. This cross-fertilisation of ideas between disciplines gives a huge impetus to our work. We assess the most advanced techniques and materials available and apply them to the medical sector.”
History of knee replacements
The first knee replacements in the 1960s had awful failure rates. Using just a simple hinge they would cause horrendous problems, often twisting straight out of the bone.
Before this, the options were even worse. In what was known as ‘fusion’, surgeons would break the bones in the leg and reset them in a straight line
Knee replacement as we know it, with implants designed to mimic the real joint, was pioneered in the early 1970s by surgeons Michael Freeman and Jon Insell, and the engineer Peter Walker.
Grateful thanks go to The Herbert and Peter Blagrave Charitable Trust for their support of this grant.