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Okay. Hi, everybody. Uh So I'm going to be talking about principles of total knee arthroplasty. Um I'm also going to throw in a little bit of kinematics. Uh This, this is uh this, this is an area that, that I'm a bit passionate about. So, uh so we'll go through it if there are any questions, just interrupt and ask. Uh and they will be quite, there'll be opportunities at the end as well. So, yeah, as as if he says, I'm, I'm on members. Are they, I'm a consultant in Cambridge. Uh uh My practice is all knees. So it's arthroplasty and soft tissue. So this is what we're gonna talk about. We're gonna talk about native knee kinematics. Well, then talk about some elements of component design and then we'll talk about mechanical alignment. So a history of native knee kinematics and how this through this theory has evolved. Uh So the needs are simple hint, right? Well, that's, well, that's what everybody thought uh in, in the 18 hundreds. So in 18 91 this chap called Thermostat Gluck design, the first hinged totally arthroplasty and he fixed it into the bone with ivory and gypsum cement. I'm sure you can all guess what the results were like. They were terrible. Um There was lots of soft tissue reaction uh infection and it was until about, it was about 70 years after that. In 1960 when Waldy is designed, the first metallic uh hinged total knee arthroplasty, you can see the range of movement is not to 90. Uh and it's an unscented design. So these were plagued by lots of migration and movement. So at the time when people thought this, the knee was a simple hinge, they designed these things and they didn't quite work. So in the sixties, this chap called Professor Freeman, along with the help of the of Swanson challenge, this idea that the needs a simple end. And it started to do some research into need biomechanics and they found that actually there needs way more complicated than a simple NGE and there are lots of degrees of freedom in terms of movement in the need. So they came up with, they, they saw this idea that the, the femur rolls on the tibia. So as you can see in early flexion, the contact points on the femur uh remained the same. And towards the end, there is sliding deeper flexion, the femur slides on the tibia and an early flexion its role. Um So it's not a hinge at all. It's, it's more complicated than that. So they came up with this idea of four bar linkage model with femoral roll back. Now, this is controlled by the help of the cruciate ligaments and does seem to, does seem to work if you're just looking at the knee in one plane. So they designed these arthroplasty uh components, the first condo to metal on Polly, um total knee arthroplasty in the sixties. And actually, they did fairly well. This, this design was then modified. I don't if you can see my, my, my cursor there, but there's, they designed this cut out at the back of the candles which were all very familiar with. Now, this was actually designed to help get the cement out of the back of the candles not to match the shape of the female, which is quite interesting. And this is the second generation of the Freeman Swanson me. And you can see they added this very, very aggressive trochlear groove. The very first ones didn't have a trochlear groove at all. So right from the beginning, we've been forgetting about the patella femoral joint, but look at the survival rates. That's pretty good. I mean, a lot of them, some of the modern implants don't survive that well, but I think you've got to, you've gotta understand these, these knees were put in for very kind of end stage. You wouldn't have a knee replacement unless you, you really literally couldn't, couldn't do anything because of your need. And then in the eighties, there was a little bit more thought into knee alignment. And there was this idea of anatomical alignment versus mechanical alignment. Up until this point, the tibia had been cut at perpendicular. So 90 degrees to the mechanical axis uh which is an anatomical, as you all know, the tibia is actually normally on average in three degrees of various. Uh So, um so Hungerford and Krakow on the left decided to put these knees in, in anatomical alignment. So actually put the, put the tibia where, where they thought it was three degrees and they did this for everyone, three degrees for everyone. Now, we have a bit more of an understanding about this. Now, um 40 years on, we know that not everyone's tibia is in three degrees of eris, but these guys were going on the average. So, um the anatomical alignment group was, was plagued by very early failure. So, mechanical alignment became very much the established way of doing knee replacements. And that's how we, that's how I certainly learned to do uh total knee replacements. And most people still do have a knee replacement sort through mechanical alignment. So that's what I'm going to talk about the for the, for the, for the majority of my talk. So then in the seventies and eighties, there's an explosion of different designs of total knee arthroplasty, anyone who was a high volume knee surgeon was designing their own implant. Um And this is why we have this market that we have now so many different implant designs, they're all very slightly different, but most of them are kind of based on the same principles. And then in the nineties and two thousands, there was even more in research into knee kinematics. And then it became apparent that the medial and lateral sides of the knee are very different. Indeed. So if you look at the medial side of the knee medial compartment, the meniscus is actually very stable and doesn't move very much. So, as you can see going for extension deflection, the medial meniscus stays very stationary. Whereas if you look at the lateral side, um uh arrows pointing to the to the meniscus in uh in flexion, you can see that it's actually rolling off the back of the back of the tibia. In fact, when you guys do a total knee replacement and you take out that biscuit of the tibia as you cut, it, look at the back of it, look at the posterior aspect of the medial and the lateral sides, the medial side doesn't have articular cartilage. On the posterior aspect of that, that biscuit. But on the lateral side, it's actually covered with articular articular cartilage. It's an intra articular articulating part of the knee. So it's part of the joint. So the lateral side is highly mobile, whereas the medial side isn't, some of the other differences are that the contact point on the medial um medial plateau remains much the same as constant for reflection to extension, there may be a millimeter or two of posterior excursion but not very much. Whereas on the lateral compartment, you can see the lateral uh the lateral plateau is con convex as opposed to the concave on the medial side. And that allows for the femur to roll much further back on the, on the, on the tibia inflections. So you can see here, I don't if you can see my cursor. Can you where I'm pointing or? Yeah. Yes. Yeah, I'll use a laser laser pointer. So it's a bit clearer. So you can see here in extension that the contact point is quite anterior on the plateau, whereas in flexion it goes much further back. So these are the differences. The other thing to say is that MCL is very thick, big structure. It's the biggest ligament in the knee, whereas the lateral collateral is very thin and lax in flexion. So these are the major differences between medial lateral compartment. So actually this whole idea of femoral rollback controlled by four bar linkage isn't quite true anymore. This is just a cross section to show you the contact points. This is the medial side of the knee, the contact point is very, very stationary throughout range of movement. And as you can see here, if you go from, from extension to flexion, the contact point on the lateral side rolls much further back. So we have a lot of femoral roll back on the on the lateral compartment. But on the medial compartment is very much pivoting around this central point. This is just a an MRI scan in deep flexion. You see this, this posterior aspect of the lateral um uh lateral meniscus. It is in that really, it's off the tibia really, isn't it? It's almost extra articular. But like I said, that area is actually covered in articular cartilage. Look how far that is anterior horn of the lateral meniscus goes in deep flexion. It's extraordinary. Okay. So this is what we've ended up with a native knee kinematics is now understood to be a medial pivot type of kinematics. So the medial side has these differences, which makes it very stable. So the whole knee pivots around that on the lateral side has is much more mobile and exhibits a lot of roll back. So what you get is a mobile lateral compartment which is lax in flexion and a very stable medial compartment is that clear so far, I'll take silence as a yes. So how do we, how do we design total knee arthroplasty implants to do the same thing? Well, it's really hard, it's really hard, it's complicated because there's a lot of things to think about. Um you got to think about femoral geometry, got to think about polyethylene shape because that really drives the kinematics of your, of your, of your replaced joint. Got to think about constraint. So are we we, you know, most of the time we're cutting at least one ligament to get into the knee. Um So do we do cut more and put more constraint on or should we think about not cutting anything? And there are designs that do that allow you to do that? Uh And let's not forget that thing you evert as you go into the knee, the patella is always there and we always forget about the patella, femoral joint and that obviously has a massive impact on in terms of the economy, attics, alignment we've touched upon because we're going in doing mechanical alignment, changing the NATO anatomy of this knee and expecting you to behave like a native knee. Well, that's probably not true for, for, for some cases at least and then talk about ligament balancing. So if we're, if we're taking out the same amount of bone, uh we want to make sure that the they were placing the same amount of, of metal and polyethylene and the ligaments are well balanced at the end. And of course, without dynamic stabilizers, then he just won't function. You can put a beautiful knee replacement in. But if the quads are paralyzed, it's not gonna work well. Is it? So there are lots of things to think about, which is why um which is, which is why we always say to our patient's knee replacements are not as good as hip replacements because it's much more complicated. And there is a 20% dissatisfaction rate in the literature. Um I'm gonna need, doesn't feel very, doesn't feel normal or it clicks or there's a bit of ongoing pain and, and, and probably it's down to a combination of these things rather than a single thing. Now, I'm going to talk a little bit about the geometry of implants. Um If we look at a lateral x ray, lateral radiograph of that knee, uh can, can I I'm gonna do some audience audience participation here. Um Does, does that, what sort of shape would you call this, this lateral projection of the knee in, in the femur? It's like it's like an oval, isn't it? So that's a bit strange, isn't it? Because all these knees are kind of designed in circular patterns, but you can actually model a circle in that post tear apart. So if you uh if you look at, if you look at some of the literature, the knee has actually three axis of rotation. So although the the axis of rotation of, of the patella femoral joint is about here, the axis of rotation of the tibia femoral joint is actually around here. So you can model it around the circle. So this has led to uh this, this kind of discrepancy between is it an oval? Is it circle has led to different divergent designs? So there are, there is a class of knee implant that creates a variable radius in terms of the femoral designs. As you can see, it's a much larger radius for the majority of the femur and then the posterior condos has this gradient. So it kind of matches the natural anatomy, but the radius kind of changes as you go into deep reflection uh is thought to be able to allow deep reflection. Um And then you've got this sort of single radius design where this post here aspect is model around this circle that were that I've just drawn on here. Um And, and it's, it's, we don't know one which is right or wrong, but uh there are different, different designs out there. I would say that that the MCL is thought to be an isometric structure which means it's the same length and tension throughout range of movement. So if you are going with a variable radius design, then you have to accept some degree of MCO laxity in deep reflection because the radius just isn't there. Um Now I subscribe to the single radius design, but there are lots and lot variable radius designs are very commonly used as well. So it's not that one is right or wrong. Uh It's whatever philosophy you you think is uh you think that works for you. So an example of single radius triathlon, uh example of variable radius is something like youtube. Any questions so far they perform differently. Um On the N J R. That's probably the F R C S question. Good questions. The triathlon really, really well on the on the N J R. But equally things like the Gentoo is one of the best surviving uh knee replacements on the market. And that's a variable radius design. So like I said, you know, that, that it's complicated slide, it's really complicated, it's not down to one factor. There are lots and lots of things to consider here. Um OK. Conformity. Now, conformity is one of the things that you might get asked in the exam conformity is degree is the degree to which the curvature on the, on the femur and the polyethylene um match, right? So on the left here, you've got a very nonconforming design and on the right here, you've got a highly conforming design, right? You can't get more conforming than matching and in the middle is a kind of a halfway house. Now, what's the difference between these? Well, um in a in a non conforming design, what you get is the advantage of high highly mobile, polyethylene, highly mobile uh the advantages is mobility. So you get a really good range of movement because it allows freedom, right allows movement. So um the proponents of this type of design say that you know, we do uh nonconforming design to allow for for deep reflection, to allow for good range of movement. But what you get uh in in in a conforming design is stability, right? So you get less you, you may have less of that sort of freedom to move. But it's actually more stable. So you get less of that mid flexion and stability, you get less movement and anterior, posterior. Now, if we think about the basic sciences and think about the forces that supplied here, if you have a very small contact area and a lot of body weight going through it, what you get is point loading. So you get high pressure, high pressure in this particular area of the polyethylene. Whereas on the other side, what you get is a dissipated pressure. So you don't get a lot of high pressure, you don't get point loading on the polyethylene. Now, what does this mean? So point loading, if you, if you're, if you're walking around, uh if you're walking around in high heels, for example, uh which you may or may not choose to do and you're walking around on a soft on grass, for example, all your body weighs is focused on the tip of the, the heel and that creates high pressure which then digs into the ground. So you get point loading and linear wear, linear wear through the polyethylene on compared to that, to compare that to the other side. If you're wearing snowshoes and you're walking on snow, you get low pressure, so you don't sink into the snow. But what you do get is a lot of volumetric wear because your contact areas much higher. So the surface of the polyethylene will wear, right. So you get a lot of these little particles of polyethylene flying around which we then no cause um osteoclasts, osteoclastic activation through the rank ligand pathway. And then you get osteoporosis and that's what we saw in the old polyethylene designs and hip replacements when there was a lot of wear. Um you'd get a lot of osteolysis. No. All right, I'll come back to that in a minute. Um And then conformity works in both ways. So you can also have highly conforming designs in the in the corona plane, which then means that you get less of that movement in terms of valgus, various movement. Uh And very extreme example of this is a constrained design of the polyethylene when we talk about constraint ladder, and I'll come back to that, that has a big post that matches perfectly into the center of the, of the femoral component, which then allows it kind of takes over some of the, the stability that the MCL and the lateral collateral confirm. And here's a, here's some, here's some evidence to back up my claims. Uh If you look at the persona, this is a, this is a medial pivot design and this is an ultra congruent design. So medial pivot design essentially has highly conforming medial side and a very lax uh nonconforming lateral side, which then in theory allows for that medial pivot um that we talked about native knee kinematics, whereas the ultra congruent has, has the same amount of congruence see on the media and the lateral side. So this is a, this is this is the contact area. So because it's highly conforming on the medial side, you get, you get, you get a lot of uh contact area, okay, but not indeed flexion because then it kind of changes a little bit. Whereas on the lateral side, it's much less throughout because your area of contact is smaller uh whereas it's very similar on the ultra congruent designs on that side. Now, what does this mean to for pressure? This is a pressure gauge on here. And as you can see with the medial pivot designs where there is an increase in contact area, the pressures are a bit lower. Remember, this is just one plane. This this conformity works in in both the sagittal and corona planes. Whereas the ultra ultra congruent ones that the pressures seem to be a little bit higher because the contact areas are a bit smaller. Although it's called ultra congruent, it's actually not as congruent as the as the medial side of the medial pivot. It's a bit confusing. So essentially what you get is um what you get with with with the higher contact area is lower pressure uh and less linear wear, but you get higher volumetric wear and and symmetry doesn't have to be essential. We know that the medial and lateral compartments are not symmetrical. So uh there are needs that match this. So for example, this is the is the Medak to sphere. And you can see the medial side is highly congruent uh uh matching uh in terms of curvature between the polyethylene and the femur. And on the lateral side, it's actually around on flats, a highly in congress highly mobile lateral compartment which fits with the whole media congruent medial pivot philosophy. Um And that's, that's what that's, this is the one I was talking about with showing use of medial side is very, very stable. The lateral side is highly mobile allowing for that medial pivot. But there are, there is a, there are, there is another way of creating achieving medial medial pivot. So for example, I think this is the, this is the persona I think which has a different radius of curvature between the lateral and the medial compartments. So the medial medial femoral conduct has a smaller radius of curvature, which then means that it has less roll back and the lateral side is bigger which allows for more roll back to in, in essence, you're more roll back on the lateral side than the medial side creating a sort of a medial pivot. But it's a bit strange because I think this one, I think the poly doesn't quite match the same philosophy. So you see lots of factors that play here. It's not just a knee replacement is it this is kind of how you, how you feel. So which, which implant are we gonna choose? Well, it's difficult, but you have to essentially understand the implant that you, I think at your stage underst understanding of what uh implant you're using is quite useful and how it's designed and what it's supposed to do. So, so for example, the triathlons quite a, quite a tight knee. So, you know, when you're putting it in, uh that's what you should be aiming for because it's a single radius design, you want the MCL to be tight at all times, whereas some of these, you kind of want to put in a bit loose. So that allows the rhythm movement. So get to know your implant. Good. Any questions so far going to move on to the next topic? So if you have any burning questions, this might be a good time. I can, I can I just uh get back to the slide with the single and uh dual radius design. Uh Talking oh It's me is Schumann. All right. Good. It'd be nice to get to know you guys go, go for it. So which one you want me to see uh the slide where you demonstrated the single radius? And uh uh yeah, I just, so this is, this is the one aspect of knee replacement design that's always sort of eluded me a bit because looking at these two knee replacements from uh you know, from the Sagittal view, they kind of look the same. Can you just highlight how, how, how the, how the how the designs are different and how they achieve sort of the bit the variable radius of the single radius kind of. Yeah, the difference. Yeah, pretty much. Yeah. So um essentially what you get with a variable radius is as you, as you work your way through here, this look at this circle. Can you see this this bigger circle? So the posterior condo all curves away from that? Okay. Does that make sense? Yeah. So there's away from that and it creates this sort of not circular but Huvelle, right? Um Oh Yeah, like this where this side uh it's, I guess, I guess it probably does so a little bit but much less. So if you were to create a bigger circle, this would still be in touch with that big circle much further away. So I guess that that's a single radius. It's kind of sitting more like this. Does that make sense? Yeah. Okay. So you're, you're based around the circle that's bigger but it further back. Um If you look at, if you look at Nick howls work, there's a really great paper he's got where he's drawn on the axis uh three axis of rotation of the, of the, of the new point. And that really explains it quite well because this bigger circle is essentially your tele femoral rotation. Yeah. And the smaller one is the is the tibiofemoral axis of rotation. Um So you can have 22 cylinders in the in that plane which, which corresponded the two different joints and then, you know, with the whole medial pivot thing and that rotation and acts your plane, there's another access through the medial joint. So these, these are the three axis of rotation. My, my two, my slides for next time that clarify things a little bit. Yeah, it does actually. Yeah, thanks. Anything else? Uh I was just uh it's armored here on the same topic. I was just wondering if uh any chance anyone or Genesis to is a single radius or no, it's variable radius. Uh Why do you ask that? No, because you raised the point of them MCL uh and being taught in and uh single radius and I've never thought about this and I never thought she should be. Uh I've never considered the multi radius with single radius and MCL tightness. No, no, most people don't. Most people just, I mean, it's, it's difficult because there's so much to learn as a registrar, right? What you're doing is trying to learn the specific, you know, sequence of events that you need to do to put in any replacement. You're looking at the, the uh the optic, you don't tend to stop and think about the design philosophy. And that actually interestingly, a lot of these, a lot of these needs come with, you know, when you search for the optic, search for, for example, search for Triathlon design philosophy, right? And it gives you a different uh gives you a different PDF with all these things written on it. Uh And most of these, um a doctor has the same and uh tune has the same persona has the same. So look, look at these things and you'll, you'll notice that the slightly different design philosophies, the, the journey is quite an interesting one because that's, that's a variable radius, but they've done lots of different things to try and make it um a kind of a medial pivot joint and the poly design is different, it's not symmetrical. So there are, there are lots of subtle subtle changes, subtle design changes between these implants it might be worth looking into if you're interested in, you can ask one more question. So I get the, the advantage of a single radius would be keeping the MCL a nice symmetric structure and it probably has implications for the stability in flexion and extension. Is that correct? Yes. Um What would be an advantage of a variable radius over the single radius of? Well, the idea of the variable radius is that uh you're not kind of overstuffing that, that that posterior condo. Also, you've got more of that more space here for the tibia to go into deep flexion. So the proponents of this say that it looks more like a lateral view of the femur that you're looking at it. So it looks more, more, more natural and it allows for deep reflection um, that, that's, um, it's not, that's not completely true because you can still get deep election with the single radius designs. But that's the, that's the, that's the argument that you get more flexion. Okay. Yeah, that's great. Thank you. Okay. So we've got, uh, thankfully later on at four o'clock who talked about history of knee replacement. He's designed the generation before the gentle, he's worked with insulin small so he can enlighten us. It's a bit of a minefield reason. Yeah. Yeah. And, and you know, you'll, you'll see the designers of these knees will say that their design is the best. Okay. So the constraint ladder now, so far, we've just been talking about the CRT, the crucial retaining, we have, it's not crucial retaining. Is it because you've cut the ACL to get it in? But uh the PCL retaining but people call it C R. So this is what we've been talking about now, if your knees unstable for various reasons, you go up the constraint ladder. So A PS has a post in the middle for the Poly and it fits into this, his camp of the uh of the femur and that, that, that substitutes the PCL, see, cut the PCL and this post stops posterior sag of your, of your tibial tray of your tibia. And then you have this highly constrained uh component. So it's uh constrained component has a much bigger post and you can see if it's much more snugly in the center of this uh of this femoral component. And that, that takes over some of the, some of the constraints or some of the uh yeah, some of the constraints that the MCL uh office. So if you've got problem with your collaterals, then you can use a constraint component uh to, to counteract that. But you see the piece of the PS, although it has a post, it doesn't have, it doesn't have uh stems with it because it, it doesn't confer a lot of stability to the components. Whereas with this, where you're putting a lot of forces through this poly and the components, you need to have stems on your, on your components in order to dissipate those, those forces, otherwise your components will come very quickly come loose as all these forces that are going through your knee are now going through the implant bone or cement bone interface. So you get much, much earlier loosening if you don't have these, these uh these stems and then we move on further uh and actually link the femur and the tibial component's via this, this hinge. This is a rotating hinge which also allows some rotation. Um because we know there is there is rotation in the actual planes. And if you take away that rotation, these fixed changes, they, they loosen very, very quickly because you're really taking a, you know, those degrees of freedom that I showed you are taking all of that away and, and getting the implant to take on all of that. And realistically, it's the, it's the implant bone interface which takes it and they become loose very quickly. So this is an increase in constraint ladder. Um It's something you need to be familiar with. Okay. So let's say we have understood all of that design philosophy. We've chosen our implant. What do we do next? Well, we still have to put it in, right? And we need to cement it well, for it to last a long time, right? Because you can choose the best implant. But if you don't put it in, well, it's not going to last very long. So we need to plan our bony cuts, need to size the implant appropriately and then we need to balance, balance the, the gaps and the ligaments. Okay. Let's move on, let's move on to this then. So this is I'm talking about mechanical alignment here. This is your, this is, these are your axes of uh of your lower limb. You can see that obviously, femur and tibia uh the blue, the big blue line, the solid blue line is your mechanical axis. A line dropped from the center of rotation of your hip joint down to your act ankle joint. And in this case, it goes through the center of the knee which uh let's, let's say that's average it's not, but let's say that's average. Um The other lines here, this is your anatomical axis of your femur. That's your anatomical axis of your tibia. Now, the anatomical access of your tibia is pretty much along the mechanical axis. But the anatomical axis of your femur isn't the anti mikel axis of your femur is on average six degrees away from your uh from your mechanic from your mechanical axis. But if you look at the joint line, the joint line is not perpendicular to the mechanical axis is it's three degrees off because your medial um uh proximal tibial angle, this angle here is 87 degrees usually. So the proximal tibia is in three degrees of virus on average. Um And that has big implications. So what we want to do with mechanical axis, we want to cut the tibia perpendicular to the mechanical access because in theory, that's, that's sort of neutralizes all the forces across the tibia as you're as you're walking. So you get equal pressures on the medial and the lateral sides as you're as you're loading it. And that's supposed to improve longevity or reduce loosening. So, okay. So here it is a closer version of it. Um let's, this is our tibial cut. You see that, so that's are perpendicular tibial cut. Now that uh this, this, this is three degrees off, isn't it compared to the antiphylaxis? But if we want a balanced knee, we want to cut the distal femur parallel to that. Otherwise, you're gonna have laxity on one side or the other. So, okay. So this is how we're going to cut our femur. Uh and that is usually in, in six degrees of valgus because your anatomical access of your femur is six degrees off from your mechanical axis. This is all average, these are all averages were talking about. Now, we can't really accurately determine where the femoral head is, but we can fairly accurately determine what, where the anatomical access is because we can put a rod up the femur in traMADol your alignment. Yes. So we can do I am referencing of the femur. So that's why we cut at six degrees off the or distal femoral card is usually six degrees. Um And when you do that, you take much more of the medial side than the lateral site. Yeah. So you would be forgiven for thinking that the lateral lateral femoral condyle is smaller than the medial femoral candle if all your knowledge of anatomy was from doing the replacements. So this is why the cut that you make of the natural femoral condyle is smaller because you're matching this perpendicular cut on the tibia. This is really crucial. Does everyone understand that? Yep. Speak up now because the rest is going to be really confusing otherwise. Okay. So let's say we've done that, then we're gonna, then we're gonna look at flexion. So we've cut our, we've cut our proximal tibia. Uh We've cut our distal femur. Now we have to cut the posterior femoral condyles to match a flexion gap, right. So this is 90 degrees of flexion. Now, how are we going to cut this? Well, we're going to cut it perpendicular to this perpendicular, parallel to this perpendicular cut, right? It's still three degrees off. So that happens to be three degrees externally rotated to the posterior condo the axis. Now, that's a very easy reference point, the posterior condo the axis because your, your, your, your sizing jig or your, your cutting block can fit against can fit underneath those thermal condo. It's, it's really easy to reference off that. So why don't we externally rotate that by three degrees? Not because not because we have a hyperplastic lateral femoral condo. But because we want to match this perpendicular cut on the tibia. Does that make sense? So you know, when you're, when you're putting that on and it's a three degree cutting block, this is why you're doing it, you're all, it's all driven from that perpendicular cut on the tibia. Does that make sense? Uh Yeah, and you're not doing it so that the femoral component is facing the patella a bit more. That's not why you're doing it. It might be doing that because the patellas lateral lying a bit laterally, but that's not why you're doing it. The reason you're doing it is to match the perpendicular cut that you made on tibia cool. Is that clear? So these are, these are M A parts in extension, six degrees on the female, three degrees of external rotation uh for uh for the, for the posterior cut cool. And then you've got referencing. So then we need to size our component because we want to make sure that we recreate the same kind of, we want to put in the same amount of metal that we've vote that compared to the bone that we took out. So you can either reference that from the back. So post you're referencing or you can reference that from the front. So let's say this is post, you're referencing. What you're doing is you're referencing your sizing, you're putting this block on and your sizing from the posterior femoral condyle. So you're sizing upwards, you're measuring from their upwards to that kind of level of the uh the thermal cortex. Okay. So that's fine. So let's say we've got it perfectly spot on. Great. See, it matches the posterior part really nicely. It matches the anterior anterior shaft really nicely. And you've got a beautiful thing if you happen to undersize it, what you get there is a is the same amount of metal on the posterior femoral condo all but you take too much off the anterior part. And this is what's this bit called on when this happens, it's not changed, right? So you're cutting into the cortex and this creates a stress riser in theory. And if you oversize it because you're worried about notching, you still put the same amount of metal work in the, in, in the posterior femoral candle. But what you get is your implant sitting slightly off the cortex. So you're overstuffing the patella, femoral joint, you're pushing the patella out, aren't you? So what you get with post, they're referencing is really accurately reproduced flexion gap. So you're, you're, you're not overstuffing that, that flexion gap, you're not overstuffing that post here from your candle. And that means that your knee will be able to flex. Well, because if your overstuffing that, if you, if you get that wrong, you'll, you won't be able to flex your knee. If you get it. If you undersize it, you won't, uh you'll have mid flexion stability. So you get really good, accurately reproduced flexion gap. But at, at the expense of the patella femoral joint or notching. So you have to get it right now. The other way of doing it is to measure from the top down. So let's say we never want to notch ever again and we never want to overstuff the patella femoral joint. Okay. Well, let's just, let's just measure from the, from the, from the anterior backwards. Okay. We can do that and when we get it right, it's perfect that spot on. If we undersize it, in this case, you're not gonna notch because you've measured it from the front. All right. So that's, that's the reproducible bit. But what you get is an under stuffing of your, of your, of your post, your femoral condyle. So you, you end up with this kind of clear space with this gap in the in flexion and patient's don't like that. If you, if you, if you understaffed the post referral condos, you get mid flexion instability. When the knee goes into flexion, your collaterals become lax and then that allows more movement and, and, and, and feels unstable. By contrast, if you overstuff it, you're not gonna overstuff the patella femoral joint that's sitting nice and happy. But you are overstuffing the post area, uh thermal condo your overstaffing reflection gap, which then means your tibia is not gonna be able to flex because there's just not enough space, your, your, your, your ligaments are too tight. Does that make sense? So, with anti referencing, you won't get any family watching and you won't overstaffed the femoral joint, but that's at the expense of accurately reproducing the uh tibiofemoral joint. So you might get insta bit mid flexion instability or you might get stiff knee because they can't flex. So it's up to you to determine which one you prefer. What's more important to you. Is it more important that you, you're recreating the deflection gap or is it more important to you to, to treat the, the patella femoral joint? Now, you need to get to know your system because some of them have uh different jigs for anti referencing and post you're referencing. Uh you can see. So this, this one is a, is an anti referencing whole says Aunt Refs a tiny little writing and this is post ref tiny little writing. So you need to get to know your, your components because let's say you're doing post, you're referencing and you want, you're, you're between sizes, you want to know the effect of over sizing and under sizing, right? And it's the same with this one. Um and some of them, some of the, some of the systems have both together. So this one has posterior hotpot, Osteria, posterior hotpot steer referencing holes and anti referencing holes. So it's all in the same, uh it's all in the same drug, get to know your system. Is that clear so far, any questions about referencing? Very common question in exams. So you're in between sizes? Yes, I guess that's the most common question. So to downsize if you're a political reference, er, is the, yes, if you're wheezy right out if, if you're a post here reference, er, and you're between sizes you can downsize but what's going to happen to you? What's happened? What's gonna happen to your femur? If you downsize your femur, not much you're gonna notch right? And have you got any strategies for preventing notching? Um, so reflection of the flexion of the component, right? Reflection of the component. But by that stage, you're kind of, you've done that, haven't you? Because you, you're, you're flexion that rests on your distal femoral cut, doesn't it? So if you're using, remember if you're using the flexible I AM rod on the femur your naturally flexing your, your, your component. Yeah, but by that stage is too late. So you can't flex it anymore. What else can you do? Um can anterial eyes, your component, you can. So uh so then, so there are lots of, a lot of the systems allow you to move your component by about two millimeters. Um You can do that. And what that would mean is your, your, your kind of making um You're making a compromise. There aren't, you're getting, you're getting both wrong, really, you're getting the flexion gap wrong and you're getting the, the notching wrong. Um But yes, that's something that you can do. Uh And the other thing you can do is uh always determine how big a notch is going to be. Really, you get your angels and go around and see how big it's going to be. If it's not a big, not what you can do is cut on the medial side because it's often the natural side notches, you cut on the medial side, allow the saw blade to come out, come on, come on the lateral side and don't go all the way through and you kind of lift up that, that anterior uh cut that you've made and smooth that over with your saw blade. Has anyone seen their consultant do that? You know when they smooth over the anterior cortex. If it's about to notch, not seen that yet. That's another stretches. So there are lots of different things you can do. Those are the things you can do. And if you are um yeah, but obviously notching is not an issue in your anti referencing. I happen to be a post your reference to because I think the the patella femoral joint is much more forgiving. There are lots of things I can do to the patella femoral joint. Uh Whereas if I get the flexion gap wrong, it's really difficult to manage. Uh patient's don't like that. So I I'm opposed to your references because I want that bit to stay uh to be to be my uh my constant. Okay. So, so then we need to make sure. So then let's say we've done, we've prepared that we've done our perpendicular cut on the tibia. We've done our distal cut on the femur and post here cut on the femur. We get a flexion gap in an extension gap, don't we? It was our extension gaps, affection gap. Now, when you do a trial or when you're putting your uh your, your gap sizer, uh you know, the paddles, you hope that this is the same size. Sometimes it is and sometimes it isn't the things that affect the, the extension gap are the distal uh uh the tibial cut. Of course, that affects both the distal femoral cut affects the extension gap and the posterior capsule affects the extension gap. By contrast, deflection gap is affected by the posterior femoral cut as we've discussed and also tibial slope and the PCL. All right, these are the things that affect it. So let's, let's do some experiments here. Let's say you get into sagittal balancing, you're, you're doing, you're balancing your flexion extension gap balancing and you've got, it's just tight. You can't put any of, you can't put your, your paddle into in an extension or in flexion. What's going on there? And what can you do anyone? Couple of tibia. Yes. A symmetrical tightness. The thing that's common between both of them is a tip, isn't it? Let's go back here. Tibia is the only thing that affects both. So if you're, if it's symmetrical tightness, it's a really easy problem. You recut the tibia. Yeah. And then you've got nice, nice balance caps. If it's tight in extension, what do you do take more of your distal? So increase your distal femoral card. You can, that's one thing you can do if you want to go straight to bony cuts. Yes. Anything else you can do posterior capsule with these post your categories? Yeah, exactly. So if you, if you do do uh an increased distal thermal cut, you'll have to do all of the thermal cuts again, right? Because that will affect everything. Um But you can release the posterior capsule. It depends on how much of a tight gap you've got really, if it's just, if it's a little bit, you release the posterior capsule, it gives you a little bit more extension. Um And in theory, you should be doing as much of the soft tissue stuff as you can before you do your bony correction. Uh but you can cut more distal femur, of course, you will have to re cut everything else as well. And let's say scenario three, it's tight in flexion. What do you do in that case? Posterior cut post, sorry, post your Yeah. So what does that mean? We just talked about post, you're referencing, anti referencing. How would you do that? Who? Yeah, it's not easy. Is it, you can't really do that because you, you then you have to take uh more bone over the anterior aspect of the team. Do that. Anything else? Soft tissue releases? So osteo which, which releasing. So depending if it's various or valgus, various, it would you would progress from uh MCL and capital. We're not talking about that. We're not talking about Corona balancing. We talk about flexion, flexion extension, right? So it's symmetrical or the medial lateral side, but it's just tight in flexion. You just can't flex the knee with the component in what do you do? Slope, sorry, increase the slow posterior slope. Yes, slope is one of the things. So it's actually a really difficult thing to deal with. This is you can get into trouble doing this. If you say, you know, when someone has a, I'm sure we've all worked with people who, who, who take an extra two millimeters off the distal femur when, when there's a fixed flexion deformity, anyone work with someone like that? Yeah, I have um so automatically take two millimeters extra. So then you get more, more extension. But what you're doing there is raising the joint line. If you take too much bone off the distal femur, you can't put it back on and it's not easy to, to, to, to deal with, to deal with a tight flexion gap. So what the things you can do? Well, you can cut the PCL a little bit that gives you a little bit of extra, extra flexion gap. But then you have to use a P S component. So you end up having to cut, cut, cut a box out to do that as well. You can, you can shift that component a little bit anteriorly. Yes, it is true. You can do that. You know you can do, you can put your, even if your post you're referencing, you can shift anteriorly by two millimeters we discussed in the same way that you would do if you were kind of thinking about maybe it's gonna notch. So I'm gonna just something that anterior you can do that. It's not easy and the fits not that great, but you can do that. But increasing the tibial slope will help. Um And this is what we talked about. You can't downsize the component and just move it up a little bit or you can distill is the femur. Um So you add a bit more, both add a bit more metal work to the distal femur. But if you were to do that, if you're adding or comments, then you, you should be putting a stem in. So that's, that's a, that's a difficult scenario. That's probably the best case. Best thing you can do to be honest if it's a big, it's a big change because then you're not falsely elevating the, the, the, the joint line, but it's a, it's a fast because you, you need to put a stem on the femur. So you're looking at, you know, if you even have that have that increase in uh in constraint on the shelf. Okay, happy with that so far. So summery balancing, if the problem is symmetrical, cut tightness, it's easy. You can't bit more proximal tibia. If it's tight in extension, you can release the post your capsule and cut a bit more distal fema. It's tight in flexion, cut a bit more slope on tibia, recess, the PCL or this stuff, enrollment or you can downsize that anterior eyes happy so far. Can I just ask the type the, putting a distal femoral Augmon when you still have a tight election gap? Yeah, but then you're converting a tight in flexion problem to a symmetrical tightness. Okay, then, then you just come to you, then you cover motivated fine. Okay. Now what we talked about, we learned that the needs a medial pivot joint. We talked a little lot or a little bit about. We had an introduction to component design in total knee arthroplasty. Uh lots more to, to learn. They're really, but it's, it's a good introduction and we talked a lot. We talked a lot about mechanical alignment principles. That's how most people do knee replacements at the moment. Any questions? Um Just on the kinematics alignment, on the first slide you had in the beginning. Um uh I think just thinking about the valgus near as well. So I presume it's not always that three degree bearers that you, you're referring to. No, no, it's not. That's the other thing I'm going to put on there for you. Uh Look up your, your hand, Bella Mons looked at a number of cinema goers. Uh So they looked at 100 150 I think, or there about maybe 1 20 normal, normal knees. So 20 year olds though are at the cinema. They said, hey guys, would you like to have a line on x rays of your knees? Somehow they managed to get uh ethical approval for this. And yes, they did and they, they plotted their hip knee angles. Uh and they found out that actually on average the knee is in various in about one degree of various most so average knees are in various. But there is a, there is, there's a normal distribution to this uh from, from a lot of various to a lot of valgus. So there is definitely a distribution. And if you're interested in this, look up the CPAC classification of knees, so you can look at uh whether the knees in various or valgus and whether the joint line is in various or Valgus. And you can plot that in a, in a grid and you get, you get nine different types of knees and there is an interesting distribution of them. Um So not everyone falls into the mechanical alignment principal, this is extra reading really and, and it moves me quite nicely onto this. Did anyone hear about this rapid unscheduled disassembly is SpaceX flight that, that, that exploded mid mid flight, successful successful space X flight. Now, this is what I'm going to do to this talk. I've just talked a lot about mechanical alignment. I'm just gonna destroy everything, but I just want to introduce you to this concept of cinematic alignment um because it is, it is a hot topic and it's coming in. Uh So this isn't, this is a POSTOP X ray of a mechanically aligned, know totally this is a perfect perfect only replacement, good size, really, really perpendicular on the on the tibia. It's just beautiful, isn't it? It's the perfect knee. And if you were to draw the mechanical alignment. It's really lovely. Falls down the center of that knee is a perfect knee. Isn't it any problems with that? You don't see any problems with that painful? No. No. Well, it probably is painful. But, uh, no, on the X ray looks fine, doesn't it? And if you look at the other patient's other knee, their other needs in various, yeah. Granted, there's a bit of arthritis but they were in various. So you haven't matched their normal anatomy. And is it any wonder that 20% of knees are still painful and have problems? So, compare and contrast that with what with what uh east in, in Oxford and this is a kinematics alignment. Now, a lot of people are grimacing about X ray thinking, look at that. It's awful. It's all wonky. But I I assure you this is uh this is intentional kinematics alignment. So you can see that to be has been cutting various and the femur is cutting about 10 degrees of valgus. Now, your, your jigs won't even allow you to do that. But if we were to look at the POSTOP, uh if we were to look at the alignment postoperatively, you can see that actually, it's matching that patient's naturally various need. And if you have to look at the joint line of liquidy, the public witty matches it to. So we haven't cut it perpendicular. This is a much more natural restoration of the patient's natural anatomy. This is cinematic alignment and there are lots of different types of kinematics alignment. There are lots of different names for them, but essentially, they all kind of follow the same principle in that you're, you're matching your, your alignment cuts to match the patient's natural anatomy. And there are lots of different ways of referencing it, lots of different ways of, of achieving uh using a robot or with conventional uh instrumentation. So this is, this is a little introduction for you guys into kinematics alignment. And I've got another talk on this, so I'm sure I'm sure we can arrange it for you guys for those who are interested. But it's uh it's, it's a, it's a, it's a hot topic and it's probably here to stay for, for the long term. If anyone has any, if anyone else wanna, if anyone's contact me, go on the website, uh got my details. They're happy to happy to talk about this stuff in a bit more detail. If anyone's interested, any final questions just with the Canham Attic alignment. Uh What's your thoughts about the longevity of these implants? So, um they're pretty good. Uh You think how has got amazing uh series of them over in California? He, they, they don't, they don't fail in various like we, we think they do. It's interesting because a lot of mechanical alignment needs, mechanically aligned needs, they fail in various, they all fail in various almost all fail in various because in my, in my opinion, they're always a bit tight on the medial site regardless of how, well, it's balanced the forces. There are just more because you, you're kind of the way you're cutting it. Um So they fail in various, which means people are scared of putting these in various because they think that's how they fail. But actually, if you're balancing it, well, they don't fail in various. So, Nick House kinematics, unrestricted kinematics align knees don't fail in various. They have slight issues with, with flexion extension in the other plane. But that's more probably to do with the slope and implant design. So longevity is not an issue in them. And if you look at forgotten joint scores, it, that's, it's higher. The organ joint, joint scores are higher in kinematics realigned knees than conventional, mechanically aligned knees and forgotten joint scores are, you know, when, when someone has a hip replacement, they sometimes forget which side they had replaced. Um So they would have a high forgotten joint score. Whereas knee replacements, they often, they often can tell you because it just doesn't move quite right, doesn't move like a normal knee, just answer the question. Um Yeah, just ask a quick curious question about the kinematics knee. Um There's obviously on that picture, the, it's quite various because that's how the kinematics live in is if you had to revise that to something with a step, how on earth would you do that because stem, stick out the side of the, yeah, I think once you get to a revision scenario, you're, you're looking at mechanically line mechanical. There's no, there's no, there's nothing that really exists at the moment other than, I guess, a, a custom implant, um, it doesn't really exist. The systems are not there yet. Sure. I think by that stage you're kind of losing the benefit of, of kinematics alignment. You multiple E multiple E operated me. Uh You just want something that's that, that moves vaguely well. Uh Yeah, nice. Is that right so far? Can I ask another one? Um So no rotation of the component. Uh Do we, so there, there are companies that built the E R into the component. So do we then is there any benefit to that? And do we then external rotate slightly more or just reference the white sides? I think that's that, that is the uh you're talking about the gen to, for example, that's already naturally extend, irritated, which then means that your flexion, extension gaps are not symmetrical, which is why you have to use the extension paddle in extension and flexion paddle in flexion because it's more of a trapezoidal gap. Um That is about getting to know your implant and how it's supposed to be put in. You should, so if it's already externally rotated, you shouldn't extending, rotates anymore. But you'd only know that if you've read the read the design philosophy and the surgical tech. So that's about getting to know your implant. Really? X okay. Thank you. Good. You're welcome. So the next talk is about uh sports injuries. Um I might have a very short break and get a cup of tea. I suggest you guys do the same. How about that? Is that okay?