Robotic arm-assisted medial compartment knee arthroplasty is a cost-effective intervention at ten-year follow-up

Listen to Andrew Duckworth, Nick Clement and Mark Blythe discuss the paper 'Robotic arm-assisted medial compartment knee arthroplasty is a cost-effective intervention at ten-year follow-up' published in the January 2025 issue of The Bone & Joint Journal.

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Transcript

[00:00:00] Welcome everyone to our first BJJ podcast of 2025. I am Andrew Duckworth and a warm welcome back to you all from your team here at The Bone & Joint Journal. I'd just like to start by thanking you all for your continued comments and support for our series as well as a big gratitude to our many authors and colleagues who take part.

That highlights just some of the great work published by our authors each month. So today for our podcast, I have the pleasure of being joined by two authors from a paper published in the January edition of the BJJ entitled, 'Robotic arm-assisted medial compartment knee arthroplasty as a cost-effective intervention at ten-year follow-up: a cost-effectiveness analysis from a randomized controlled trial'.

So firstly, I'm very pleased to be joined by Mr. Nick Clement, who is a fellow editorial board member here at the journal, and one of my awesome colleagues and friends here in Edinburgh. Nick, great to have you with us. Thanks very much, Andrew. It's nice to be here and such a lovely introduction. Brilliant.

Love it. I'm glad you approve. And secondly, Nick and I have the pleasure of being joined by one of our awesome colleagues from the West, Mr. Mark Blythe from the GRI. Mark, it's great to have you with us. Delighted to be here. Thanks. So guys sort of maybe Mark, I'll start with you yourself. I thought, you [00:01:00] know, I was hoping you'd maybe give us a brief overview of your experience with robotic knee replacement over the past, you know, decade or so.

And maybe some background with that, of the original study that this work is based upon. So Andrew we got first involved with the MAKO robotic system around 14 years ago, and we're lucky enough to get the first system to be used outside of the of the US. It was originally designed to be used for just unicompartmental knee replacement.

And it was of interest to us, certainly because I felt there was this technique gap because unicompartmental knee replacement, even in experienced hands, it can be problematic. And so we were very excited with the technology and of course, therefore wanted with this new technology to try and.

compare it against the standard of care, which was using traditional instrumentation and was the Oxford mobile bearing implants. Yeah, no, absolutely, Mark, and I think, I think that's a good insight of what the, like you say, the standard of care was at that time. And Nick, if I maybe come to yourself, you know, we all know Mark and you have, you know, [00:02:00] You've published a huge amount of literature in this area, some of which you've published in the BJJ as well.

Can you maybe give us a take on the state of the current evidence for robotic knee replacement as we stand at the moment? I think there's more and more papers every day, kind of coming out with robotic this, that and the other. I think there's more systematic reviews and meta analysis than there are actually, than there is evidence at the minute.

But it's kind of, you've got to be really careful what you look at and what you read, because obviously there's loads of different robotic systems out there. And likely with different results. So I think it's really difficult to get a real grasp on the evidence because there's something new every, every, every day, more or less with a new spin on things.

But certainly you said knee, but this is really about unicompartmental knees as opposed to just total knees. So from certainly the uni side of things, we published a review in the journal a few, a few years ago. And it go goodness. Yeah. Time flies ever 2022. I think it was. And, and, and that showed basically the, that's the robot and the robot was more accurate, funnily enough, it's kind of what it's designed for.

But at [00:03:00] that point in time there, there was no difference in the functional outcomes. I think there was slightly less complications overall in the robotic lot. But that's using PROMs that were designed for a total knee replacement, kind of, and Mark's previous papers have really expanded on how probably the outcome measures that we use are a bit useless to try and pick up the small difference that we're trying to detect.

But certainly from some from registry data. More recently, the survivorship is better with a robotic knee, and that's probably not arguable anymore. Now, certainly at least a couple of percent better. Yeah, absolutely. And I think you sort of touched upon it and we're related to that review. And I remember we did a podcast on that as well.

And so maybe it's a brief introduction to this paper now. You know, you've obviously looked at the cost, you know, so what, what made you look at cost-effectiveness in the way you have done in this paper? And you talk about it in the introduction quite nicely. I think kind of, that's the next big thing, isn't it?

A cost like, like this robots, certainly my first game was a million quid. Why on earth they ever put it in [00:04:00] Glasgow? You think somebody would have, Anyway nonetheless it's come down in price, got a little bit, a bit better, but, but certainly within a healthcare system that we have, public healthcare system we have in the UK, we've got to justify the cost.

And I think that's kind of been the big, the big driver of, certainly for me is to try and justify this new technology. Mark's the same, really. He's kind of spurred me on. Certainly we published a Markov model back in 2019 ish. It was the first one I ever did. It was, it was, it was good to do on some early outcome data.

Andy Pearl's data from HSS on survivorship and using the, the then known outcomes EQ5-Ds and kind of pieced it all together. But this, that was all, I'm not gonna say made up. That's what a Markov model is. Best guess, isn't it? Where the exciting thing with Mark's data, it's real, it's like, it's absolutely solid.

And he approached me at the Scot meeting. A couple of years ago, maybe it's 2022, we then wrote the five year data up because Mark was wanting to do a Markov model with that data, but there was no need to because it's real data. You don't have to make [00:05:00] stuff up. And then that led onto this 10 year paper, which is obviously, I'm not going to spoil the thunder of what we're going to discuss, but kind of, this is real data with real follow up and real, probably real costs.

Absolutely. And again, that sort of takes us on quite nicely to sort of the, so the meat of the paper and the, and the, how you sort of did it. So if you know, just to sort of clarify for the readers, the aim was to perform an incremental cost and utility analysis and assess the impact of differential costs and case volume on the cost effectiveness of robotic arm assisted medial unicompartments on the arthroplasty and how that compares to manual.

So I mean, Mark, if I may come back to yourself, going back to the original paper, I think Can you just give us a very brief overview of the sort of inclusion exclusion criteria who was in the study and particularly what the two interventions were for the groups? Yeah. So, so to put it simply, the inclusion criteria were patients who were suitable for a unicompartmental knee replacement for medial osteoarthritis of the knee.

And so they have to have intact ligaments. They have to have disease that is limited. [00:06:00] to those joints in the main, that part of the joint in the main. And so in our practice at that time we were quite enthusiastic unicompartmental knee surgeons. So it was around 20 percent of our practice. It's around 30% now but it was pretty much standard unicompartmental patients.

And they also had to be a able to comply with the study protocol, of course, for the study. And also they had to have isolated unilateral disease, so they couldn't have significant pain in the other knee that might affect the PROM scores postoperatively. And so we were able to recruit over a two year period to, to the study.

And The early, the, the the study was designed to look at accuracy of surgery. So how good the surgery was performed at delivering the preoperative surgical plan. And we were able to demonstrate that the robotic system was much more accurate at [00:07:00] delivering the implant position in all six in, in, in all six planes or all three planes.  

It's much more accurate at delivering the pre operative plan. We looked at problems and Nick's alluded to the early outcomes and we were unable to demonstrate any difference. One of the difficulties you've got with unicompartmental outcomes is that they are universally very good.

And you alluded to that with the problems that we've got, there's a massive ceiling effect and really very difficult with those problems to demonstrate any difference in outcome between two types of interventions, because they're based really on like the Oxford score is based on on activities of daily living, rather than more discriminatory activities and And so we weren't even with with the Oxford score, we weren't able to demonstrate any difficulties.

Absolutely. And in terms of the, you know, the sort of planned follow up for the study, Mark, how did that sort of pan out? What were the sort of time periods that you were looking at them after the intervention? So, compliance with follow up has been good we've not, we've had some deaths and it around 7 percent in each [00:08:00] arm of the study at 10 years, which is probably pretty standard for this patient population.

We have had some loss to follow ups where we've not managed to to interview and to examine patients at longer follow ups. Overall, we've managed to see around 80% of of our patients. We have that great advantage in Scotland, of course with the our National PACS National Archive system where we can search on PACS to look for any revision procedures that might have been pre performed.

So we're pretty confident that we've captured all of the patients at 10 years if they've had a revision in the NHS, it doesn't exclude. That does, of course, exclude patients that might have had it done in the private sector, but we have very low rates of private insurance in Scotland. And of course, it doesn't include anyone that might have had a revision elsewhere, for instance, in England.

No, absolutely. That makes total sense. And Nick, if I could maybe come to you before we sort of move on to the results of the study, you know can you just sort of clarify for our readers, sort of as basically as you can, you know, [00:09:00] the calculation of the QALYs and how that and the costs and how that was done.  

So QALYs aren't really very hard. EQ5Ds are used to assess quality of life gain or health rate, quality of life. So if you gain if you go from 0. 6 to 0. 9 post op, 0.6 to 0.7 post operatively, you've gained 0. 1 of a EQ5D. If you keep that for 10 years, that's, that's point one times 10.

That's one. So you gain one QALY. Qual quality adjusted life year. So it's pretty simple. And then you just divide that by the cost. So if or, or the cost, sorry, is di is divided by the QALYs gained. So if somebody costs a thousand pounds and you gain one QALY, it's 1000 pound per QALY.

And then you got a cost per QALY up that NICE suggest. Kind of ranges on tonight, 20, 000 cost per QALY is what, what's, what's really Talked about, but that was based on data from 20 years ago, in fact, even longer than 20 years ago now.

And that was what a cost or what the estimated cost was for dialysis, I believe. And they thought that was a good intervention and it [00:10:00] cost about 20, 000 per QALY. And they thought that was a good number, but that was 20 years ago. So, so I don't know what that, but it's never really changed to be fair. No, absolutely.

And in terms of the, the, the, you had sort of three costing models that you, you used, can you just sort of briefly describe those and any sort of assumptions you also made as part of the analysis? Well, those three cost models were really down to Mark because he really tried to hammer, hammer the data the best he could to, to try and make it believable because really the cost, the, the, the, the real cost analysis that we should do includes everything includes it also includes the two infections and that definitely makes it the dominant procedure.

The dominant procedure is basically something that costs less and delivers more, which is impossible in orthopedics, I think. But anyway, there might be something out there, but that's kind of the aim, whether we ever get there or not. And Mark didn't believe that. He thought, well, it was probably not. And he's right.

So we excluded the infections as just a random event. I think it was one early one. Mark wasn't really [00:11:00] immediately post op, the wound one that may or may not actually been infected, but was managed as infection just because there was a wound problem. And the later one, I think the hematogenous about four or five years, I can't remember, but so we took them out.

And then that left, I think five revisions. Well, but then it was all pre operations excluding infections. That was the next model. And Mark still didn't like that, even though it's real. That's what we should have presented. So, and for a third model, there's actually a fourth model to be fair, that Mark even We didn't make it into the paper because we were just, it was getting confusing.

So then we went for a a third model that actually excluded the arthroscopies because Mark thought there might be a bias in patients that they're going to MAKO send them away as opposed to you going to Oxford. Actually, you might get an arthroscopy. So, so we excluded those. I think it was three, I think sat there for five revisions.

Yeah. And that's what the, the, the third model was based. There was a fourth model based on because of the five revisions, I think. Two of them or three of the five had had loose base plate two had loose and we tried to base the [00:12:00] cost-effectiveness around that and it was still less than 20, 000, but it didn't make it into the paper Yeah, no absolutely And you've sort of alluded to that already Nick if we move on to those results, you know in terms of the revision rates You sort of described it, but they were sort of So, five patients in the manual group revised to TKA, three had a knee arthroscopy, and two had a DARE, you've described there were no re interventions in the, in the robotic group, is that correct?

That's right. And, and probably the other thing to emphasize is that, that, that the five revisions in the Oxford group, or the manual group, is actually less than the average NGR revision risk at 10 years. That works out as something like a 7 percent revision risk. Five divided by 65, I think in that group the revision risk is around about something like 7%.

So that's lower than you'd expect, than the 10%. So it's still quite low. So even though it sounds a lot, Yeah, it's actually what you'd expect from a mobile bearing. Absolutely. And just before we move on to sort of the, you know, the implications of it, what did you actually find, you know, sort of briefly in terms of the costs [00:13:00] when you did all your analysis?

That's a, that's a, that's a massively open-ended question. Well, it was more cost effective, Mr. Duckworth. I, I, I, I think, I think it's really, that's, that's a, that's a, like, yeah. W we could be all day about how much things cost and, and, and, and, and, and how much the robot should be, how much the implant should be with, with the robot, and whether you should reduce the cost of the implant.

But can I, could I back butt in here because I think. The cost effectiveness depends on what you put into the model. So we, in our study, it was to, to put it simply around a thousand pounds additional per case, and around 500 pounds of that was the cost of the robot around 2000, under 50 for the CT scan, about 250 pounds for the disposable.

But of course, those are just costs that were correct at the time that we did the study, but those costs are variable because it depends how many procedures that you do per year in your unit, then the unit cost per case for the robot goes down. It depends what a CT scan, whether you report it or you don't report it.[00:14:00] 

and what the disposable costs that you've negotiated with the manufacturer are. So all of those are variable, which is why it's difficult to be certain. But if we say it's a thousand pounds per case, if you then say that the cost, the average cost of a revision is around 20, 000 per case, then you do the math to work out how many cases that you have to do to make it cost effective.

And so you have to have a revision rate that at 10 years is around 5 percent different to make it cost effective. And Nick's right. I think we, I did struggle with the concept of including the infections. This was a relatively small study. These were random events. They're massively expensive to treat and they really do skew the data.

So it was much more comfortable to exclude those. But even if you, by excluding those, you still find at 10 years that robotic unicompartmental knee surgery is cost effective. Yeah, absolutely. And so [00:15:00] if we sort of move on to the implications of that, Mark, what do you feel from this study alone are the key take home messages?

And I suppose with any, you know, limitations of the study and the data itself? Well, I mean, I think the first and obvious limitation is that it's a relatively small study. It was powered to look at the accuracy of surgery rather than any particular cost cost effectiveness analysis. So there is a concern that in a wider study with more surgeons in a multi center.

setting that we wouldn't find the same results. But I think it's pretty encouraging that for some relatively modest upfront costs, because of course those costs over time will come down as it does with all technologies that there are cost savings potentially to be made the complication revision rates.

In that systematic review that you alluded to earlier have [00:16:00] been shown to be less with robotic unicompartmental knee surgery. And so I think that the benefits are there and I think it's just a matter of time before we prove it in, in, in other wider and larger studies.

Yeah, no, absolutely, Mark. And Nick, if I come back to you in terms of the actual findings of your paper, you know you know, in terms of the, you've alluded to already, but in terms of survival, how does that sort of fit with the other literature and the registry data? Well, yeah, I kind of, Certainly early data from Andy Pearl's group relatively large cohorts, three, 400 patients showed very low revision risks early on up to five years, but the more recent paper he published or they published as a group 10 years, it did show the revision risk did increase not quite as.

but it was getting up to eight to nine percent. I think it wasn't quite the ten percent, so it did increase, but certainly early revision risk was less. But when you look at the Australian Registry, just, I just looked at it last week for presentation as that happens and certainly they've got data out to six and seven years [00:17:00] now, and there's a definite difference between, Of 2 percent there and there abouts at that time point, which is significant and kind of what would you have if you had a, if you had to put, so basically the number to treat has 50, isn't it?

So if every 50 knees that you're going to do, you're going to save one revision. Sure. That's not like, like, that's a good thing, isn't it? Yeah, absolutely. And in terms of, cause I thought it was interesting was in your sort of. penultimate paragraph when you talk about, you know, if you extrapolate it in terms of how you make it cost effective or it's cost neutral.

Those figures are quite interesting, you know, in terms of, you know, it's not what I almost expected. I expected it would have to be bigger than that. But like you say, reducing the cost of the implants used for robotics by 141 pounds or more would make it cost effective in a unit undertaking 400 a year.

That's, that's quite amazing. Yeah, like And it is kind of mind boggling, even in units that you're sitting in currently. Yeah. [00:18:00] The partial, the manual partial knee replacement costs us around about 800 pounds more than the robotic knee replacement does. So actually it's probably cheaper to buy a robot and pay for the consumable part, which does vary in price depending on how much discount you get.

This price is a thousand pounds, but there's always a massive discount. So that, that probably, it'll be definitely, it'll probably be definitely, it'll probably be cost neutral, but it'll, it'll be definitely cost effective because actually we're paying so much more for the manual implant that we don't normally have on the shelf.

Absolutely. Yeah, that's very interesting. And Mark, maybe if I finish with yourself, I, you know, I, I asked this question to both of you, I think actually in our podcast two or three years ago about, You know, is it, does this now prove that robotic uni is a cost effective intervention, but from what you guys have said, is there, where do we go next?

What, what more data do we now need, or do we need any more data to prove that? That's a great question. I think this this [00:19:00] simply adds to the literature. The problem will be that when 10 year outcomes and revision rates that already that the model that we've and the funding model that you've got will will be different.

And Nick's alluded to this, you know, in terms of this. The number of cases that you do and the cost that you pay for your implants. And so the, the, if we look at our general surgical colleagues, they've used robotics to change the, the, the, the, the pathways that patients go through so that all of the care is centralized at area in with units that do robotic malignant prostates, for instance, or low anterior resections.

And so. You can imagine a, a world in the future in orthopedics where you have national treatment centers opening up doing high volumes of arthroplasty, where the, the additional cost of having a robot become really very low indeed. And you have much more control over your surgery. And hopefully with that reduced revision breach, which we'll see across the, the board that [00:20:00] will absolutely be cost effective in time.

 A good take home message for the future and where hopefully, hopefully things will be heading. Well, both, I'm afraid that's all we have time for. So thank you so much for taking the time to join me and congratulations on a great study. Another great bit of work from you both, which has clearly added a lot to the, more to this literature in the area.

And it was great to have you both with us and to our listeners. We do hope you've enjoyed joining us and we encourage you to share your thoughts and comments through our social media platforms and like regarding our podcast today and the paper itself. And we hope thank you again for joining us.

Take care of everyone.