Dr. Steven Haas delivers a talk on how to achieve physiological alignment using the anatomical design of the JOURNEY™ II TKA System. Dr. David Rovinsky delivers an informative talk on the benefits of a using a robotic-assisted approach and the anatomical knee implant design, followed by a brief demonstration on how to plan a CORI™ TKA case using an interactive, on-demand planning tool- CORI™ Virtual Planner.
I'm gonna go back to our first session, which was on alignment and I'm gonna talk about physiologic alignment, what it is and how to achieve it. Ok. Uh There's my disclosures that they are relevant. I helped design things for Smith and nephew. Well, you know, the expectations and demands of our patients are much greater. They wanna ski, they wanna hike, they wanna play racket sports and they wanna do whatever that patient who has a knee is doing in the middle. I'm not sure what it is, but they're doing it and they want to do the stuff like that. So the demands of our patients are much greater and we all know historically, knees weren't doing as good as hips. You know, the hips were out soon. They were really happy all the time and you always had a percentage of knees that weren't as happy. And you also had a lot of knees who just couldn't do things that they wanted to do and their activities were decreased in sports as opposed to increase which you always always saw on hips. And there's been a lot of work as you know, done on looking what is normal. What are the normal patients like? And, and uh, Bellman did some very elegant work and showed that constitutional, we're a bell curve but we're not a bell curve really around the middle. We're more a bell curve around a little bit of a and males, about 32% of females, about 17%. So we normal is not necessarily perfectly straight. It's not way out. You don't have lots of people who are, who are way out of that. But there are people certainly who are not straight and that's their normal alignment. And also that most people have a oblique jaw line, right. So oblique joint line. So restoring the joint line, obliquity is natural. That's what it should be. OK. There we go to CPAC. So you saw this and we talked about it a little earlier. But you find that 75% of people have that vous femur and Tibby and end up being an oblique jaw line which they call distal, apex, apex, distal. But it effectively just means they have val femur and a tie. And the degree of that gets some different alignments and go into different categories. But basically, that's the alignment. But total knees weren't built that way. The traditional total knee was really only built to match this. They had essentially, they were 90 90 the symmetric part symmetric. If you did that sme in a normal knee, they would be symmetric and that was only a small percentage of people, so you match a small percent. So we all talk about these new alignment strategies, function alignment, which is essentially modifying the alignment a little bit to balance the knee kinematic alignment, which is sort of the extreme you go whatever they are or whatever they used to be, or you determine they used to be and match that with no limits. Uh which I think, um probably is, is a bit extreme. But having uh restricted kinematic is uh probably more likely to like most people would agree or an atomic alignment, which essentially is that dates back to uh a fixed alignment for everybody. So you can accomplish that in two ways. You can go say, well, what's the best way to achieve it? Well, you could take that standard, you know, total knee of, of 40 years ago, that was built with symmetric condal, symmetric tibia and say, I'm gonna take that and I'm gonna change that alignment to match that anatomy. OK. And you could do that, but you end up with some pretty funky looking x-rays because they really don't because you have to modify it a lot in some of the patients. Or you could say I take it like the average anatomy and have asymmetric condoms, asymmetric poly and match like the average or typical anatomy. So that's the way the journey was designed. The journey essentially said we're gonna take the cuts of a typical knee, do the bone cuts we like to do in a total knee and reassemble those parts. And that's the shape of the implant. And it's thicker immediately on the, the femur thinner, laterally, conversely, it's thicker on the lateral side. So you end up with your same rectangular space, it just divvied up with an oblique joint line, which is more typical. So you end up with this three degree, typical, the average joint line with three degrees of obliquity. Ok. So, but the fundamental is caring about joint line obliquity was something we've cared about for over 15 years. We knew that this was important and that's why it was built this way. And that's where the concept of three for free comes for you say, well, what does that actually mean? Well, here's what it means. If you take that C pack and you say I'm only going to change my cuts by three degrees. And I think most people would say three degrees, I can vary the cut, three degrees. I can go three degrees more or less on the femur, I can go three degrees more or less on the tibia. If you said I'm gonna restrict it and say I will only change it from mechanical neutral cuts by three degrees. You cover almost, you can match precisely what the anatomy is of that patient in almost every patient. So minor modifications can do that. Now, what you say, well, what happens if I do with a conventional or older implants. Well, you, you don't match many, you're matching at best, 40 or 50% at best. And that means all the other ones, you have to go way out, you have to start modifying 56 degrees of variation of cuts. And while I'm really comfortable saying I'm gonna put a two degree or three degree various cut on the tibia, I'm not so comfortable even with the robot saying I'm gonna do a six degree cut because six degrees not sort of on the heavy patient. I'm not sure. That's a good idea. I think biome, that's what, you know, huge loads of bone quality gets worse. And if you're a degree off which a robot can even be a degree off, then you're seven degrees and all that is that good? Uh We don't know. And so you're really pushing the limits and, and there's no reason to it, it, it, it forces you to do something that is really doesn't make a lot of sense. Let's say you're even more concerned. I don't like my cuts by more than two degrees. And I think everybody would say two degrees. You can get away with right, two degrees. You cover most with the journey, you actually can match the anatomy and C PAC what their natural anatomy was in almost everybody with only a two degree variation and with the standard implant, you're not even close, right? So it makes sense to make the, the implant like the typical anatomy. If you do that, you don't have to vary very much to get the, um, to match their anatomy. And why do you not wanna vary? Well, the obvious reason if you start varying by a large amount and in heavy patients and shown you get various cuts in heavy patients on the tibia that you're getting yourself into trouble, you put huge loads on that tibia and it's, it's, they, they can fail. Another thing I talked about that 3D anatomy. And I think this is really this to me is, is, is as, as important as any, the trochlea of all the implants that you, that are symmetric were designed to be put in three degrees or more of external rotation. And they were also designed to be put in, in a position where a by the im canal was about five or six degrees. And what that did is that's where the trochlea was placed to be in the right place. OK? That's the way the implant was designed. That's the way they were made. OK? The problem is, is now, oh, and if you look on the, the that's actually taken from a a it's actually make drawing, you can see the implant and the robotic drawing and lined up if it was normal. Now, what happens if you make a tibi cut? Now, I've said, well, I'm gonna modify a lot. I made a lot of in my tibi o cut, I then had to internally rotate my implant to match that flexion gap. Well, when the intern of the implant, it was good in the back in the back of the knee, but the front of the knee now also had to be rotated, that moved my trochlea immediately. And this is an actual picture. I actually took it from a slide someone had. And if you look at that, look where the trochlea is. It's not in the right place. The trochlea is now in the wrong place. It's a simple, it's a very simple. The trochlea was not designed to be put that way. So that knee is lined up with that bone and it doesn't match. And that's gonna happen all the time because you're changing one thing in a way that it was not designed to be put in. It's just as simple as that when you start wearing it, they weren't designed to be put that way. You have another issue. Now, when I put the knee in a typical alignment, I line it up. And that's the way you typically put on a femur, right, with a symmetric implant, right? And you actually over stuff or don't, don't even uh you put more metal back on the lateral side than uh the bone you removed. And that aims the trochlea up the center of the femur. Well, that was the way they were designed to do now because I'm following the anatomy, I stick into more vous alignment now that trochlea moved more immediately, right? Because it's aiming not up the middle of the femur now because it's in more valgus than it was designed to be put in. So again, you're just, you're making that knee the, the hurting the patella to try to help your balance and journey has shown over the years even with us, non customizing it just by because you're getting the average patient, even if you just did typical mechanical alignment, you're actually matching closely. Most patients. You showed we've shown that you can increase satisfaction that way. And we've published on that before showing higher satisfaction scores than any of the other needs. 35 out of 40 which is really off the chart compared to other ones and and survivorship is actually in younger patients even better than we had in the in registry data. So we haven't compromised in any way survivorship by doing this method of reproducing joint line obliquity. So I would argue that that uh frequently have dissatisfied patients. An atomic asymmetry of the journey knee essentially allows you to restore the natural joint line obliquity again. Good idea. A great idea. Uh And glad we thought of about 15 years ago and everybody's coming to terms with CPA. Um And it, it allows for safe personalized alignment in almost all patients where you get superior functional results, high return to sports and recreational activity and high satisfaction. Thanks very much. Uh I'm Doctor David Rainsy. I'm an assistant clinical professor at the University of Hawaii. And I've talked to you about coy robotic assisted knee replacement and the impact of implant design on our planning. I'm a consultant for Smith nephew Ortho grid and also VR and I've been involved in computer software prior to medical school and have been doing integration of technology to orthopedics for the last 20 years. What we all recognize is that our total knee patients want to perform high level activities. And in Hawaii specifically, this is surfing and this has required a redesign of the total knee. And I got involved with the journey project in 2004. And we had access to CT data, MRI data and virtual simulations. And we came up with a more an atomic design of a knee replacement. And the goal is to restore the joints, pre arthritic joint shape and alignment. And this has grown into a family of implants from the UNI the PFJ to the journey to XR, which is a cruciate sparing knee to the journey to B CS which is a cruciate substituting design. So in order to do the surgery properly, it's important to understand some design concepts behind the implant. So the goal is to make a cut perpendicular to the femur mechanical axis and perpendicular to the tibia mechanical axis in extension and then externally rotate these cuts in flexion so that we can create rectangular extension gap inflection gap that are equal and 19 millimeters in height. What's different about the prosthesis is it puts back what you take away. So the tibia implant is thinner immediately and thicker laterally. And the femoral implant is thicker immediately and thinner laterally. So this reproduces the natural oblique joint line of the knee. And if you're using a symmetrical type implant, this is what's behind the kinematic design where you're adding some bogus to the femur, adding some virus to the tibia. And again, this gives better attention to the ligaments. The MC L and the LCO the femur is an an atomic design that matches the normal contours with a larger radius of curvature immediately than laterally. And the tibia is concave immediately and convex laterally. So it's the intimate association of the femur and the tibia that drives poster lateral rotation as you go into f reflection. And the concept is that if you reproduce normal anatomy with the oblique joint line and the femur sitting anterior on the tibia, then you can reproduce normal kinematics. And this also benefits patellofemoral tracking. And you can see here how the B CS implant really mimics the natural motion of the knee for patients. This is a faster recovery because they're not fighting the implant to get the range of motion. And when I transitioned from a legion implant to the journey implant, my physiotherapist noted that my patients were improving much faster. So if we were gonna do this knee replacement with a measured resection technique using manual instrumentation. We'd have to make a number of decisions and to demystify the planning process we've made it so that it mimics the same decisions that you're making with manual instrumentation. So the first decision you're making is extension gap shape and that's your distal thermal cut alignment. And what we're trained in fellowship is to get standing x-rays measure the mechanical axis of the femur and then choose a vow that pushing that matches this cut. So we're making cut perpendicular to the mechanical axis. The next step is deciding the extension gap size. So we're making a cut off the distal femur. This is a feeler gauge off the medial femoral combat that cuts 9.5 millimeters and often people are taking a plus two cut for a flexion contracture. What we've noticed with robotics is that this is a big cut. This often elevates a joint line two or three or four millimeters and this dog bone shaped cut is always too much bone. So our goal cuts are gonna be matching the circus typically and much more shallow cut than we're using a manual instrumentation. The next decision we're making is the flexion gap shape. And most commonly people are doing three degrees external rotation relative to the poster conor axis. And again, this is not suitable for every patient. Some patients require two degrees. Some patients require five degrees, but we're doing our best to make these decisions with manual instrumentation based on an atomic landmarks. The next decision we're making is the flexion gap size. And we want to be equal to the extension gap size. And we do this by moving the femur anterior posterior or changing the femur size. And we do this again with Fieler gauges and I think mechanical alignment is difficult to get this right. And when I did use manual in implementation, I always use the gap balancer to set my rotation and my Ferral component and adjust the component sizing. So we know that gap balancing, this ligament information is very important. And there's lots of studies that show that if you use gap balancing and planning your femoral component rotation and sizing, you get less left off and better outcomes. Next is making our tia cut and the guides are set to make a 12 millimeter cut off the lateral side. And this is because that's how thick the implant is, but often this is a large cut larger than what we need. And we end up putting in more polyethylene than we would like. And the goal I think is always to put the Tibby in the best possible bone in the most proximal bone and of course, to match the joint line. And then once we've made all these cuts, we can check our extension inflection gaps. But once you've committed to these cuts, it's very hard to make changes. So if you found, for example, that your flexion gap were tight, it would be challenging to reapply a block and downsize this femur and then we put our trials and do our final ligament releases and hope that we get it right. So I think with manual instrumentation, we have a lot of challenges. We're making many decisions with very limited information, particularly it's difficult to decide thermal rotation and position. You don't have the ability to prototype to assess the impact of your decisions before you cut bone and you don't have any way to assess the accuracy of your cuts. So this has driven a lot of us to transition to robotic assisted surgery. And the core system has registration of the surface of the knee anatomy, including the mechanical axis of the femur and the tibia along with ligament tension to help us with our intro planning, which I'll show you is very quick and intuitive, fast and flexible. And then once we've made our plan, we use this handheld CNC computer NME control machine to remove the bone where the metal goes, it's very efficient and very precise. So when we're thinking about planning the journey to knee, there are some concepts that are important to recognize. Typically, I'll do a slight under correction to minimize a soft tissue release. The next thing is I know where the joint line is and I can stress the importance of maintaining the joint line for optimal knee function I think with manual instrumentation, we've seen that we're often elevating the joint line unconsciously, since we have an an atomic implant in the journey, we focus on the less affected side and the journey to implant functions like a Precontoured plate. If we get the less affected side and a virus need the lateral side. Correct, then the implant automatically puts the medial joint line where it needs to be and we can balance the ligaments around that with releases if needed, positioning of the femur is critical. And we're gonna add external rotation to the femur because we want the flexion gap to be very tight. Again, the intimate association of the femur and the tibia is gonna drive that poster lateral rotation. If you're loose inflection, you're gonna have disordered motion which is very uncomfortable to the patient. So to get the best performance of this implant, we need to have tight gaps throughout. And of course, we're putting the tibia in the best bone to maintain the joint line. So our planning algorithm steps and I'll run through this in the simulator are routine and straightforward. First step is selecting your component sizes and we can do this with preoperative templating. And also the core system will give you your component sizes. Typically, the tie is one size smaller than the femur. And we want to select the fem component, that's the largest component without medial and lateral overhang. Then we adjust the extension gap shape and we do this by setting the distal femoral cut angle. So these numbers are relative to a cut that is perpendicular to mechanical axis. So knee, that's in high valgus, I might leave in one degree of valgus or correct to neutral, neutral knees, we leave in neutral. And then as patients have progressive, increasing degrees of varus deformity, I'll add one degree or two degrees of virus to the femur. A deformity from 11 to 15 degrees odd two degrees to the femur and one degree to the tibia, which is a powerful correction that affects extension and flexion gaps. But for this anatomical knee implant, if you have a virus more than 15 degrees, you should really think about a symmetric component like the legion. So that's extension gap shape, extension gap size is determined by your distal femoral cut level. So you wanna leave enough room for the component, which is typically 9.5 millimeters off the medial femoral condo. Then we adjust our thermal component rotation. I start off by using the default three degrees of external rotation. But it's very common for me to add one degree additional to again, tighten up that poster lateral side. Then we adjust our thermal component saal position and this adjusts our flexion gap size. So I can move the femur anterior poster or even change the femoral component size quite easily and then see the impact on my ligament balancing. And then we center the tibia component and set the proximal tibia cut level to match the less effective joint line. And then you see these positive and negative numbers. This means that we're loose laterally and tight immediately. And what that means, the negative and positive numbers is how the computer is interpreting the tension on the ligaments in an uncorrected position. So this is the positive number, a virtual overlap immediately. And this, this is this is a negative number, a virtual overlap immediately. And this is the um positive number laterally, which is a virtual gapping. But once you put your trials in, then you have actual measurements and then the ligament imbalance that's left after you've planned, your surgery will dictate your planned releases if needed. So if you're tight and extension immediately, MC L, if you're tight inflection immediately, post remedial capsule, and this is very common in a various knee tight laterally, an extension with the knee is it band. And if you're tight laterally inflection, then you're starting to release poster lateral structures and you should think about a constraint component. But for the journey to B CS, we really want to have less than one millimeter gaps throughout the full range of motion to maintain that intimate contact. And this is different than the journey two Xr which is the cruciate retaining knee, the design of this is different. So the planning is gonna be different. And in the journey to Xr, it's really critical to maintain the joint line. So flexion contractors that require elevation of the front line are an absolute no go and you want to plan this like a medial uni and a lateral uni. So this means that you're really thinking about a true resurfacing of the knee. So in a various knee, we're adding a little material back immediately to do to wear, matching the lateral side, we're not externally rotating as aggressively. We're internally rotating the prosthesis slightly to match the AC L footprint. So these design features will depend on the implant that you're choosing. And our ligament balances are gonna be like a uni immediately where it's 2 to 3 millimeters in extension and inflection and a lateral uni which is three millimeters in extension and an opening gap 4 to 7 millimeters inflection. So, understanding the prosthesis and knowing your goals will let you plan it correctly and we should look now at some virtual planner cases and I'll run through the algorithm with you. So we're gonna look at a very typical various case if you look on the bottom right screen range of motion is 6 to 1 46. And so they have a slight flexion contracture and they're starting in five degrees of varus and the computer automatically places the implants very close to where you would start if you did this with a standard manual instrumentation. So this uh number is zero degrees of vari so neutral cut relative to the mechanical axis of the femur cutting 9.5 millimeters off of the medial side. So this is what you would typically do with your standard instrumentation. Usually though with a feather gauge, we might make a larger distal femoral cut because there's some medial uh distal femoral wear. So that's a pretty typical cut rotation here is zero degrees and um the computer automatically externally rotates three degrees relative to the poster condor axis for this deformity. And this is zero degrees relative to white size line. So if we're looking at a cut again, 2.5 millimeter difference between media and lateral, that's representing about three degrees. The tibia, you would of course externally rotate a little bit so that it matches the medial third of the tibia tubercle. And then you would again manually move it to center it on the bone and then your instrumentation typically takes 12 millimeters off of the lateral side. So in this case, this is what you'd end up with, with your cuts with your manual instrumentation. And what you would notice is that you're very loose an extension. And uh the way you would try to fix this is you can't distal your femur anymore. You'd have to add back some poly thickness to tighten yourself up an extension. And the consequence of this is that you would end up using a 12 millimeter poly and you'd be very tight inflection. So you'd have a knee that may be felt balance and extension. But this patient might have trouble getting range of motion. The great advantage of using the robot is that you can prototype virtually and see the impact of your decisions before you commit to any bone cuts. So if we reset the poly thickness to nine millimeters, we can run through our planning algorithm as follows. So I like to make my plan on this virtual uh cutaway screen because it lets me see the uh joint line view and we can reset our ephemeral position with this button here. And this is something we use frequently because when we have the uh fellows planning our cases, um often I'll reset it and then show them how to do it from this starting position. So the distal femur cut in our algorithm for a five degree vas deformity, we're gonna add a one degree verru to the distal femur cut. And when you're adding various orval this, you're gonna change the overall mechanical alignment. But as long as you're within three degrees, we know this doesn't affect longevity. And this gives us um a 10 millimeter cut immediately which is um close to the thickness of the component at 9.5 millimeters. And um it looks to us that we wanna match the thickness of the component and that gives us a better balance. So you can now see on our lateral, more normal side, no, within half a millimeter, our external rotation we like um is at three degrees. And this gives us a good balance and we can look at our, our position of our femoral component. Again, um, you know, we're slightly tighter inflection than we are in extension. We can look at our position of our thermal component, we can blow this up to give us a better view and see that maybe we're, you know, overstuffing posterially slightly. And again, we're making half millimeter adjustments. These are very small adjustments. We can look at what this will appear virtually. And I think this is a very safe cut. When we subtract our implant, we can see that we have a nice grand piano type shape that we're familiar with. So we can add our components back and go back to our screen for the B CS component. We typically use a three degree post year slope. Again, we've kept our rotation here, but now we recognize that we're loose in extension and we're loose inflection. And the best way to fix this is to cut less tibia, which is something we wanted to do. This looks like we're, you know, making a very large tibia cut. So my typical cut off the tibia is 10 millimeters and it looks like if we make a cut of 10.5 millimeters, we have very well balanced gaps on the lateral side, 0.4 millimeters 0.4 millimeters. And this gives us a nice tight knee. Um And again, that intimate contact between the femur and the tibia is gonna drive the poster lad rotation and we're putting the tibia in the best bone possible and matching that normal lateral joint line. And I don't mind that I'm 0.2 millimeters tight immediately. This is what I'd expect from a, a mild virus deformity. But adding that virus to the distal femoral cut prevents us from having to do a medial release. And you would expect us to be post to aed tightness because the patient has a flexion contraction of various deformity. So when you clean out the back of the knee post immediately, often this problem is taken care of and that's what's gonna get you that extension. So I'm very happy with this plan and this would give you a very well balanced knee.