Ian McDermott is a Consultant Orthopaedic Surgeon and Founder of London Sports Orthopaedics. Ian was the youngest Elected Council Member and Trustee in the history of The Royal College of Surgeons and he currently holds an Honorary Professorship at Brunel University, London, in the School of Sport & Education. Ian specializes exclusively in knee surgery, and he is a designated ‘Center of Excellence’ for meniscal transplantation and also for the use of biological glues in cartilage replacement. Ian also specializes in high-performance partial and total knee replacement surgery, and in 2012 he was the first surgeon in the U.K. to implant a ConforMIS G2 patient-specific knee prosthesis. Ian has completed over 100 ConforMIS cases to-date, and he is now part of the ConforMIS Surgical Visitation Program, teaching other surgeons how to implant patient-specific knee prostheses.
Medgadget editor Tom Peach spoke with Ian at the Minimally Invasive Surgery Congress in London to discuss the patient-specific revolution in knee surgery.
Tom Peach, Medgadget: So Ian, why do we need patient-specific knee prostheses?
Ian McDermott: As a society we’re much more active, which is great, but that means that as surgeons we’re now operating on younger and younger patients –people’s expectations for the feel and the function of their knee replacement are much higher nowadays. Currently, around 15 to 20% of patients are unhappy after their knee replacement surgery. With about 70,000 knee replacement surgeries a year in the U.K., that’s a lot of unhappy people. One size and one shape definitely do not fit all, and that’s where patient-specific implants fit in.
Medgadget: Knee replacements are now a very common surgical procedure, but how does the process work with a patient-specific knee?
Ian McDermott: The process starts by taking a CT scan from the hip to the ankle, with high-resolution views around the knee joint, to get an exact 3D model of the patient’s individual anatomy. The prosthesis is then designed to fit the exact contours and shape of that patient’s knee perfectly, requiring the absolute minimum of bone removal. As the whole procedure is patient-specific, a set of custom cutting blocks are provided to help implant the prosthesis perfectly into that patient’s knee.
The actual prostheses are cast, as they would be for a conventional implant, but they are then precision machined to the patient’s anatomy. The cutting blocks are 3D printed from nylon, so all in all it only takes 6 weeks from the CT scan to the custom prosthesis arriving for the procedure.
Medgadget: What is it like using these custom-made prostheses in the OR?
Ian McDermott: First, because the system is custom-made, you don’t need lots and lots of different sizing options – all of the necessary surgical kit fits neatly into just one box, which is amazing compared to the stack of boxes you get with a conventional implant. The first few times I did a replacement with the ConforMIS knee the theater staff were panicking because the box was so small that they thought that all of the kit hadn’t actually been delivered.
Complete knee and jig assembly for the ConforMIS iTotal patient-specific knee system. Image: Conformis.com
The actual procedure of fitting the prosthesis is frankly very easy. Particularly for the femur, you can actually put the cutting blocks on with your eyes closed, the fit is that good. That level of fit is not just making my life easier though, it also means it’s very hard to get anything wrong intra-operatively, because everything just slots into place. With a standard prosthesis, you end-up cutting the patient’s bone to fit the prosthesis, often having to take away more bone than one might like. With the patient-specific implants, the bone cuts I make are very much smaller. When I went back to doing a few regular knee replacements after having worked with the custom knees for a while it just felt horrible, and the traditional kit seemed archaic and brutal.
Medgadget: Is this level of implant customization altering your role as a surgeon?
Ian McDermott: It does take away some of the surgeon’s personal judgment. As a surgeon, you’re used to making intra-operative judgement calls and decisions. With the patient-specific knees, the surgeon ends up having to put a lot faith in the people who have designed and manufactured the prosthesis (who aren’t with you there in the OR), and you have to rely on them having got things right. When I first started using these knees, that did worry me (as all good surgeons have at least some degree of OCD) – I thought, well, what if the engineers have got it wrong and it doesn’t actually fit? I’ve now done over 100 cases and I’ve never had a single problem with fit. It’s obviously still a good idea to have a standard off-the-shelf knee on standby to calm nerves in case anything goes wrong, but I’ve never had to abandon a single patient-specific case and revert to an off-the-shelf prosthesis.
Ultimately, the learning curve is just like that with any new prosthesis; knee surgeons don’t like to change the prosthesis they use because it worries and stresses them, and quite rightly surgeons tend to be conservative and cautious in their approach. However, the more cases you do, the less you stress about it, and you become more confident and trusting of the equipment.
Medgadget: What about the results – does a custom knee perform substantially better than a standard prosthesis?
Ian McDermott: There’s a growing body of literature on patient-specific knee replacements, and it’s showing some very positive results. Fundamentally, with a custom-made knee you’re taking away significantly less bone – that’s good for a number of reasons: first, you’ve got more bone left should the patient potentially end up needing revision surgery later in life; and second, less bone removal means a larger surface area for the cemented joint, and hence a stronger and better fixation between the bone and the implant. The blood lost during the procedure is also reduced with a custom knee because you can be less invasive, there are less exposed raw bleeding bone surfaces left in the knee (because of the better fit), and the procedure is actually slightly faster.
Really, the most important outcome for me is patient satisfaction – that is the absolute gold standard. As I mentioned before, with a regular knee prosthesis satisfaction rates are around 80 to 85%. With a custom knee, patient satisfaction rates are about 95%. Now, the way to look at that is not just a 10 to 15% increase in happy patients; that’s at least a two-thirds reduction in unhappy patients, which is massive.
Medgadget: Ok, so what does it cost to have a bespoke knee replacement – does all of this precision come with a hefty price tag?
Ian McDermott: Obviously, the custom implant is a bit more expensive than a standard knee replacement, but not by as much as you may think – the increase in cost for the entire procedure is less than 10%. Plus, given the lower rate of complications, you may actually be saving money using a custom prosthesis.
To me, getting a knee replacement is like buying a suit: would you rather have an ‘off-the-shelf’ suit from anywhere, that is cheap and that roughly fits ‘OK-ish’, but only if you are a standard size and shape, or would you rather have a ‘Saville Row’ suit that is expertly tailored to your body, that will fit perfectly and that feels great when you wear it? I’d certainly go for the latter!
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