‘Partial Knee Replacement Explained’
Mr Gavin McHugh

I’m going to be giving a talk with regard to knee replacements but from a slightly different angle and the talk is entitled “Getting away” with a Uni? Hopefully as we go on I’ll be able to explain a lot more. Some of the slides actually have quite a bit of information in them and I only will be touching over some of the detail but it’s just so that there is more information there for people who actually want it and I’ll try and as to say keep things as simple as I possibly can.

So the first question is obviously what is a uni or a unicondylar knee or it’s often referred to as a partial knee replacement as well. The knee joint I always say to people is one big joint all right essentially the capsule of the knee goes right the way from the top to the bottom of the joint and but within the joint itself there are three separate areas which sounds very non-technical but that essentially rub off each other. The first is where the kneecap or patella rubs off the front of the femur and the second and third then are where you can see the diagram in front where the femur divides into two knuckles one on the inside, one on the outside and they essentially rub off the meniscus or cartilage on the inside and the outside respectively and a piece of the tibia. So, essentially there are three areas within that joint that make contact with each other and a knee replacement as we know it essentially replaces all three of those but we know that there are lots and lots of people who get wear within one of those areas and either of the three areas can be replaced. The most common by far is the one on the inside knuckle which is would be a medial unicondylar knee replacement and these account for about 90% of the partial knees that I would do the outside to a lesser extent. Then lastly simply for me would be the patellofemoral or the one at the front and if you just look then this is a sort of a classic X-ray and the two views are slightly different one is just with the knee a little bit more bent but you can see that on the inside knuckle there’s a bit of narrowing and with the knee bent a little bit more the two ends of the bone essentially make contact with each other and that would be what we call isolated medial compartment arthritis within that knee you can kind of see where and I would often compare this to the tread on a car tire or something like that there whereby the wheels aren’t balanced and essentially the tire is pretty bald on one side and fine on the outside. That’s unfortunately where the analogy kind of ends because what we do then is we just take off the tire and replace it with a new tire whereas if you could imagine if it was possible to rethread part of the tire that’s essentially what the idea of what a partial knee would be.

This is then just a x-ray then, it’s actually the opposite side of the knee so it’s not the same patient’s knee at all, just to complicate things the x-ray to the left is the view from the front the middle one is the view from the side and you can see essentially what you do with a partial knee is that you replace a bit of the end of the femur and a bit of the end of the tibia all right and as I say  for me the majority of these are on the inside knuckle as is shown here. The x-ray on the right is a front view of a total knee replacement for comparison and you can see there where you essentially replace the whole end of the tibia and the whole end of  the femur and what you have to do in order to do that there is you got to take out the anterior cruciate and you may or may not take out the posterior cruciate as well depending on basically the configuration of the knee itself. Every total knee replacement relies on the ligaments on the inside and the outside and whereas a partial knee replacement relies on having everything there, so you maintain your cruciate ligaments as well and this is one of the big benefits when it comes to the knee in that it tends to feel and move and behave much more like the native knee and hence they a big part of the reason that that I’m such a fan of it. It is by far the most natural feeling knee that I can give back to someone where possible.

Now the first thing I like to say about partials is to break the myth that some people often say ‘oh they’re very difficult to do’ and that’s something that’s just simply not true like everything else it’s a technique that just needs to be learned and performed well but they can be extremely repeatable and this actually is one person that had replaced both sides on at the same time and essentially the cuts of bone that have taken off were exactly the same, the implants that I put in were exactly the same on both sides, and actually the time was exactly the same on both sides as you can see from the machine and it just goes to show that you can actually execute the plan really well with a partial knee and as a surgeon it’s great to have something that is extremely repeatable that you can do pretty much the exact same thing time and time again and that’s one of the best ways where we give best outcomes for our patients.

Again there’s a lot of detail in this slide I don’t expect you to know it but it just to explain a little bit in that partial knee replacements a number of years ago were sort of very much limited in that there was like under 5% of knee Replacements that were performed were partial knees and the these criteria that that were described a number of years ago placed very sort of strict conditions on what you could and couldn’t do a partial knee on and since that the Oxford Group which would be a major users of partial needs have come, they’ve revised all these criteria and essentially up to about 50% of knees in all commerce now are potentially suitable for a partial knee rather than the old sort of from the old criteria it was about 10% that would be suitable. Now in saying that well it’s up to half of knees are potentially suitable for partial knees, the uptake of them remains relatively low and I think that’s for a number of reasons I think there’s a lot of fear, there’s a lot of sort of ignorance out there about how they can perform and again as I say I just want to go through and sort of bust some of these myths if that’s possible. So the one myth that other surgeons will often say to me is that I just don’t see them as and I don’t see patients that are suitable for partial these and this is essentially just not true in that it’s like everything you see what you want to see and if you’re a fan of using a particular operation you’ll see lots of people with it, if you’re not you simply won’t but there are lots and lots of patients out there who are suitable for partial knees.

Now then if we move on and look at some of the indications, so the classic indication essentially for a partial knee would be bone on bone wear in that affected compartment and that’s something that we tend to stick with although there are indications whereby people who present with a pretty nasty tear in their cartilage and have a bit of wear often the problem with them is that they’ll often get worse if you go ahead with keyhole surgery and certainly there are lots and lots of patients out there who we know that have unfortunately actually almost fallen off a cliff in terms of their symptoms get worse after keyhole surgery again there are very sort of definite indications for arthroscopy or keyhole surgery but we have to sort of remember that sort of middle-aged patients with these what we call degenerative tears in the cartilage, often it’s very much more sensible to take things a lot slower and we’ll often just try an injection or a couple of injections to try and let things settle down. One of the big problems with what we do I suppose is that everything doesn’t always obey the rules and quite often we’ll see patients with nasty tears in the cartilage quite a bit of where and the knee can completely settle down and they can remain symptom free for potentially years and years. Others with even simpler tears just don’t sometimes get better and settle down and as I say these are the ones who potentially I would consider going in a little bit earlier with a with a partial knee but obviously this would be after sort of several consultations and potentially a trial of a couple of injections before jumping in with something even like a partial knee.

Busting a couple more of the sort of the myths with regards to the maximum weight with regards to partial knee and the short answer is there isn’t one, now there’s potentially maximum issues with regards to going ahead with an anaesthetic or going ahead with a spinal but in terms of the pure load on the knee for a partial knee itself there isn’t actually one and this initial criteria was a weight of 82 kilos and this is complete nonsense this just doesn’t exist now and indeed it can be a really successful operation and patients essentially of all sizes. There’s the postoperative there, were both knees at a separate sitting actually.

Then if we go we then look at sort of, this believe it or not this picture on the right is a postoperative picture and this is actually it’s six weeks following a partial knee replacement and you can see that the bend is pretty much a complete knee band and this is something that you would very rarely see with a total knee replacement. Certainly, it would be extremely usual at 6 weeks and anecdotally we used to always sort of settle for sort of 90 degrees after a few weeks but now we look to sort of 105/110 degrees bend in someone after with a total knee replacement at six weeks but certainly not the like of this bend which is pretty much 150 degrees. The questions then that you need to sort of ask yourself in terms of a getting a knee and is that as you can see there would you prefer a knee that feels better functions better but may not last you as long, we’ll talk about the outcomes in years to come down the line.  Would you prefer a knee that has a quicker recovery or one that potentially lasts a bit longer, would you prefer a knee with less risks but that has a higher failure rate and I often say that is a total new replacement a procedure for a patient or the surgeon and sometimes the answer I think honestly is that it’s more of a procedure for the surgeon and that what I mean by that is that with a partial knee you have to be prepared to sort of deal with other issues down the line in years to come and these shouldn’t necessarily be looked at as failures at all but that the bottom line as I say is, would you prefer a knee that feels better, moves better and allows you back to more activities.

Now and this is the problem in that what we do with regards to a consultation it’s unfortunately an awful lot to try and sort of get your head around when it comes to sort of having you know your history taken, your examination completed, looking at any Imaging and then having a discussion on what or where we go from there and it can take a bit of time and it is kind of hard to get your head around for all of us never mind someone who’s just hearing about it for the first time. The problem with that I see is for informed consent is that well we can’t assume what we think patients want to know and some patients love a lot of detail with regards to what they’re going to get done other people just want it fixed, but we cannot assume that we know what is best for the patient and those days are essentially gone whereby it is now a question of going well which would you potentially prefer. If we sort of look at again there are lots of numbers on this graph but basically these figures are odds ratios for different risks and problems comparing a partial knee with a full knee and essentially a partial knee if you look at all the risks on the right, a partial knee replacement comes with a lot less risk. So, you can see most of those figures or half that there are 5 or less that sort of number, in fact death at 30 days which is thankfully extremely unlikely is less than a quarter that of a full knee and all the risks I sort summarize them by saying on average the risks are a half to a third that of a full knee. Now the downside then is that you’re potentially 1.4 times more likely to have a further operation within the next number of years, so you have to be able to sort of decide whether you want less risk or do you want a knee that’s going to last longer and longer. The other thing then the last factor to bring into that there is well how does the knee feel and perform and this OKS is the Oxford knee score and essentially the higher score the better patients do and you can see that the risks of having a much better score or more satisfied knee is significantly higher with a partial knee than with a full knee. What we know from lots and lots of literature is that on average following a full knee replacement about 90% of people are happy, which leaves about 10% of people who aren’t happy in some shape or form and that’s unfortunately quite a significant number. The big issue with that obviously is that well once a knee is replaced there is in general no going back there are potentially other things that can be done but you certainly can’t go back and swap it back for the knee that you had prior to surgery that’s for sure.

Then if we look at a score called a forgotten knee score and you can see here that so basically the higher the score the better and the forgotten the score is as it does as it says on the tin, it’s a questionnaire that assesses how people feel their knee is forgotten for various activities so It’ll ask you things like you know getting in over a car, going downstairs or with general day-to-day activities, how much awareness you have of that knee so obviously a higher score the better and you can see there the partial scores for the scores for a partial knee replacement are significantly better than that of a full or total knee replacement. The next myth I would like to bust, is that someone saying well I don’t have all my total knees do well and unfortunately this is just not the case a total knee is unfortunately is not an operation for everyone and it comes with potential problems.

So the other alternative procedure when it comes to fixing isolated arthritis within the knee is a procedure called high tibial osteotomy and essentially if you look at the diagram on the right side it involves cutting the tibia bone opening it up on one side and a wedge shape and then fixing that with some plates and screws and the idea is that you offload the warn side and basically take the load away from the worn side and increase it on the non-worn side and younger patients, indeed patients of multiple ages of this is procedure that can work well. This is often essentially it’s an operation that preserves your joint which it technically does but one thing that it doesn’t necessarily do is result in a more normal feeling joint than that of a partial  knee replacement and that’s been demonstrated in several studies.

Again if you just if you look at potentially the risks of partial knee replacements compared to the osteotomy group as well again there’s plenty of evidence to say that the risks are actually lower in the partial knee group not higher as one would sort of  potentially think and there’s more information there for patients who wish and again the myth just there is the joint preservation has potentially less complications than something which seems more invasive as an a partial knee.

Again then if we look at how partial knees behave in terms of return to Sport and this is something that is becoming more and more important for us and certainly something I would hear of more day to day in that I see lots and lots of patients some in their 30s, some in their 40s with well-established arthritis, on one side of their knee and but also lots of patients in their 50s, 60s, 70s, who are very fit and active and want to remain that way. Obviously it’s a much bigger a challenge for us as surgeons to be able to get patients back toing all the activities that they want to do and  just purely with regards to osteotomy one would sort of intuitively think that you’re more likely to get back to sports when you have your old your old joint and in fact that’s not necessarily the case at all and a partial knee replacement is every bit as likely to get people back to sports. It is very important I suppose that to a certain extent I put the brakes on there a little bit in that if people are running marathons, if people are involved in really high end activities they have to know that any form of either osteotomy, replacement be that a partial or a full may not reliably get them back to the level that they wish to, it isn’t necessarily the case but it certainly can’t be guaranteed and ultimately I suppose any form of replacement or even an osteotomy is an end of the sort of the road procedure and it’s much more to get you back doing your normal day-to-day activities rather than high-end sporting activities as such.

Now if we look then at return to sports for a partial you can see there that there’s plenty of data here that that lots of people can get back to you can see the activities hiking cycling, swimming and even winter sports are quite possible to get back. Now a lot of these activities I often say to people that it’s much more of a philosophical question rather than a sort of a physical one in terms of can you get back well a lot of time you can get back to them the question is do you want to sort of that run that risk of something happening and again if someone wants to go back skiing I have certainly no problem with them with even with a the total knee or partial they potentially can but they have to realize that there is always a small chance that they could have a fall and run into difficulties but that can happen either with or without any replacement for sure any and year to year we see lots of the results of these.

Another myth that it’s often out there is that it’s harder to actually convert as either an osteotomy or a partial knee replacement down the line to a full knee replacement that’s in patients who say several years down the line, say their arthritis has progressed and an actual fact I would generally look at a partial knee replacement as something that keeps your options open. If you’ve taken pretty conservative cuts and I mean by not taking off an awful lot of bone then years down the line patients can generally get away with a standard knee replacement rather than anything complicated. Now if they have had a full knee replacement early on then potentially taking that out and converting it to a full knee or a further full knee is essentially a full revision procedure and that is considerably more difficult. Again I frequency see patients who’ve had osteotomies in the past and it’s not an easy total knee replacement down the line so in many ways a partial knee is something that keeps options for the future open and not close them.

If we look at sort of the results of a partial knee this data again there’s loads and loads of numbers there but there’re just the various different types of partial knee and essentially the physic ZUK which is the partial knee replacement I use, if you look at the 15-year results and this is the UK joint registry data which is for a partial now is out to 15 years. You can see that at 15 years there’s been about an 8% failure rate with these which is 92% survivorship at 15 years and this compares to about a failure rate of about 6% for a full knee so it really only falls very marginally behind a total knee in terms of the potential outcome and this is with obviously with getting to keep two thirds of your own joint. So as I say they people often think oh it’s not going to last and actually fact it tends to last very well and this graph on the left side is an interesting one and this is from the New Zealand registry and essentially what they looked at, they looked at Oxford knee scores which I mentioned before so the lower the score the worse patients are doing and the number on the side is the chance of getting a revision procedure and essentially what they showed, so the two bars at the bottom are the partial and full knee and essentially what they showed in New Zealand was something really quite interesting in that if you had an unhappy partial knee you were much more likely to get another operation rather than an unhappy full knee. Basically to translate that phrase is that well you’d over if you came back and your partial knee wasn’t doing well a surgeon would an average take it out and put in a full knee if you came back with an unhappy full knee you were essentially told well listen there’s not much we can do you’ve had your knee replaced and that’s it and so that really potentially even skew the data as well and that it doesn’t mean that full knee replacements out there are all happy it means that the ones that aren’t happy are all too often told that there’s nothing else that can be done for them. So that’s something that you have to sort of bear in mind when it comes to looking at the sort of survivorship on these things as well and that registry data only essentially looks at how many have been revised they don’t really there are parts of them that’ll look at the scores in terms of how patient satisfaction but the main emphasis is on survivorship of the implant themselves and so the last minute I’d like to say there is the results are simply not true they can behave really well.

So just a few take home points as I say there’s lots and lots of data to go through there your own time if you want to look at the some of the slides and but for me when it comes to a partial knee I would often look at the physiological age for the patient as opposed to their actual chronological age, in that if someone is a really good 75 year old there is absolutely no reason why they shouldn’t have a partial knee replacement and likewise someone is an excellent sort of an active 40-year-old for me they can potentially still have a partial knee replacement rather than the alternatives which we spoke about. I think it is extremely important that we maximize injection therapy before going down the route of any significant operation really. I mentioned to sort of beware of the keyhole surgery and this is something that is still done it still has a role but it is important to know that keyhole surgery and lots of these knees that have a bit of wear in them simply won’t fix them and I often say to those is with every case that we look at and see we should be there asking ourselves can we get away with a unicondylar or a partial knee replacement and as I said earlier in about 50% of cases the answer is I think we can. In terms of where we sort of fix them if you’re knee is a bit bowed we aim to slightly under correct you as in not leave you completely straight and this means that we don’t increase the load on the on the outside half of the knee then as well and thus it should be very rare that any arthritis within the knee will actually progress.

This sort of last lady is just one interesting little case to pop up and it was a 45y old who’ previously fractured her tibial plateau and if you look at the first x-ray you can see the sort of the pretty big hole and in the tibial plateau on the outside so this is on the opposite side to the vast majority and the problem there is that well and again it’s even more dramatic on the MRI scan but the problem there is that that’s quite a big hole to fill and a full or total knee replacement in someone who’s 45 years of age is anything but ideal, but with this degree of essentially the defect, your options are quite limited. So what I what I did there was to go ahead and put in a partial knee on the outside and you can see that essentially like it built the joint right up again it straightened out her leg which was pointing essentially the wrong direction beforehand and yet was quite a small procedure compared to full knee replacement and thankfully she’s done very well since. So as I say are lots and lots of different options for partial needs and all I say to people is that well that they keep an open mind in terms of looking at those options and what’s the right and best option for them but for me in approximately up to 50% of cases a partial knee is an option so I hope this hasn’t confused everyone more than giving them some more information but it’s just to give an overview of what exactly a partial knee is from my point of view and a lot the advantages of it that sometimes aren’t considered.

Yeah funny that’s an interesting way of putting it and perception on things so the reality is that day case hip and knee surgery has been done for quite a few years now right across the world. Equally with total knee replacements and partial knee replacements as much as hip replacements now the big question is if I had my knee replaced would I like to go home the same day and the answer is absolutely not, and I would say that actually to counter that argument I would say that hip replacements hasn’t really progressed at all it’s not. So the most significant progression we’ve had in hip or knee surgery has probably been the use of tranexamic acid which is to stop increased bleeding it is reduced bleeding a lot so something such a simple medication that’s been around for a hundred years has humbled us all. Back to the whole idea of the day case now you even with hips like I mean if I had my hip replaced I’d like to go home after one maybe two days that’s the sort of time where I think is the sweet spot. Where your pain is controlled, you’re confident and you’re independently mobile, now it’s quite possible to go home the same day because quite often you’re loaded up on all the local anaesthetic that’s in the area but to say and I don’t mean to knock this as the idea it is a little bit gimmicky and that you’re kind of like sent out whilst you’re still quite good and then the rest is up to yourself and obviously some very young healthy people can absolutely fly it but I mean you’ll see anyone after a joint replacement, you’ll see their confidence grow day one, day two and even day up to day three so I would basically say listen to people my advice would be listen take it, take the love when you can get it right you know right it’s a big bad world out there and often you know there’s no harm whatsoever in a bit of TLC you know for that first couple of days.

I would say well a little bit of both right in that you get it done when you’ve a lot to gain by getting it done. So we know we’ve been through that a knee of any option variety isn’t an easy option right it’s the recovery is hard and it’s often several months all right but I mean if it’s causing you day-to-day disability, day-to-day pain its holding you back from doing your activities you like to do then it’s very reasonable to go ahead and get it done. Likewise what I sometimes don’t like to see is someone really quite old just getting sort of put off with another little injection to tide them over for another few months and then potentially the best window opportunity is running out but at 74 you’re off nowhere near there at all you know so there is time and again most people by the time it comes to they’re like going yeah I’m ready, I’m ready for it you know.

So absolutely I mean Durolane is one brand of hyaluronic acid injections which we we’ll frequently use, so sort of they’re usually next in line from steroid injections as the sort of stepwise increase in injections that we have. The next sort of would be like PRP or platelet rich plasma injections as well and then up from that which you’ll hear some people mention is things like stem cells but back to the hyaluronic acid yeah I mean it’s simple to try it’s a very low risk profile and absolutely if you’ve had a break that is going to you know ultimately end up with something more significant it’s well worth a try and you simply know if it works for three or four weeks it’s going to be a waste of time. If it works for several months then it’s well worthwhile trying and a lady back today just for brought the injection stuff with her she got 18 months of complete relief with injections all right now that’s you know that’s towards the other end of the spectrum doing very well but it still happens quite routinely so it’s very simple do and worth a try.

Even believe or not January last year would still only be just beyond a year and a half you know but at sort of nine 10 months that’s not unusual at all so we have data to show that knees continue to improve for up to two years after surgery which is really quite remarkable and quite often not quite I could say the a time you’ll see the odd grumbly knee at sort of six, nine, 12 months even, that actually goes on to do pretty well so I would never say always or never in this game all right but it still isn’t necessarily run its course as of yet. Replaced knees are sometimes just not even in terms of swelling sometimes the tissue around them is just a little sort of thicker and feels a little bit stiffer and I often think that the females are more likely to sort of perceive a sort of like or describe a tighter band around the knee they just they just seem to more perceptive in that regard do I have definite evidence on that no I just see it from time to time so I would say It’s not unusual particularly at this stage and there’s still considerable hope.

Yeah so things like walking and hiking I would consider normal day-to-day use all right and implants like hips and knees are very much designed to take that load. What they’re not necessarily designed to take just as well are a lot of like twisting type of sports so I would say the walking hiking all absolutely fine on it. Now interesting that they put their age for the two as well in that if you look at say UK registry data which is sort of probably the most similar to Ireland in terms of the spectrum of things that they’re done and if you look at the survivorship say for a knee replacement 10 years 96% of overall knees are going strong at 10 years right at 15 years that might drop down to I think it’s about 91% and somewhere around 85% at 20 years. Now if you break things down into age that you actually had the first procedure and they tend to do it in under 55s, under 55s that 96% straight off the bat is down to 90% at 10 years. So the in essence in younger people the results tend to be worse, but all of this is still an odds game and you’ll see plenty of people who had their first knee in at 45 and the thing is still going strong at 30 year. So very difficult to put an answer to that there at some stage one of them will probably cause trouble right and need something doing with again.

So walking with a straight leg will probably not load the Patellofemoral joint in the same manner so assuming it’s just in on the patella it’s unlikely to be as sore for that reason just you’ve really no load going through there with a straight leg whereas as you bend it the load progressively increases. Quite often what you’ll find is if you think of it I suppose full on arthritis in any area of the knee is a bit like a tar road where the road is completely worn what people often have is like a little pothole on the road where there’s a little area that’s worn and what could be happening there is that that little pothole just manages to engage with another little pot hole at a certain angle so people will sometimes describe it say when they’re driving a car or something that just that angle let say 30° or something is enough to really lift them out of it as such in terms of not in terms of acceleration but in terms of the pain and so it could be something like that as well is potentially causing it.

So the options are well I mean depending on the scans if she had cartilage removed from one side there is a fair chance that these are knees that would be suitable for partial knees right which is the first thing that would jump to mind from a from a surgical point of view. Further keyhole surgery and those knees is not going to be the answer, injection therapy which we’ve talked about is an option in terms of trying to tide things over at 57 not something like an osteotomy I wouldn’t really consider and potentially depending on how worn they are then full knee replacements, if partials aren’t suitable that’s really the gamble but that’s the problem in that we kind of have an all or nothing approach and that the injections are sort of the least we can do and then it’s a huge step up in terms of partials and full knee replacements.