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Mastering Orthopaedic Implants - Knee Replacement

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Summary

This webinar series is designed to help medical professionals understand the evolution of Total Knee Replacement (TKR) implants. It will cover the history, biomechanics, and biomaterials of the implants. The target audience is junior doctors, medical students, and other health professionals involved in trauma and orthopedics. The session will include a lecture, multiple choice questions, and opportunities for questions. This is the first of seven webinars in the series and is presented by Mr A Kaur, a consultant orthopedic surgeon at Queen Elizabeth Hospital. Attendees will explore the development of TKR implants from the pioneering surgeons like Ferguson and Neil in the 1800s to modern designs, such as the low contact stress prosthesis and the total condylar prosthesis. The introduction of high density plastic poly and bone cement metha methacrylate will also be covered, as their advances contributed to the evolution of TKR design.
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Description

Overview:

This course is designed to provide a comprehensive understanding of orthopaedic implants.

Topics covered will include the history of orthopaedic implants, the different types of implants available, the indications for implant surgery, and the surgical techniques involved in implant placement.

Target Audience:

This course is designed for orthopaedic surgeons & residents, orthopaedic nurses, and other healthcare professionals who are interested in learning more about orthopaedic implants.

Learning objectives

Learning Objectives: 1. Learn the history and development of total knee replacement implant design from over the last five decades. 2. Understand the difference between the anatomical and functional approaches to total knee replacement surgery. 3. Appreciate the importance of patient satisfaction and implant longevity in total knee replacement procedures. 4. Analyze and discuss the advances in materials, including high density plastic and bone cement, and instrumentation used for total knee replacement surgery in recent years. 5. Compare and contrast the features of the different types of total knee replacement implants, including the polycentric and condylar implants.
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Computer generated transcript

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The following transcript was generated automatically from the content and has not been checked or corrected manually.

Good evening, everyone and welcome to this series of webinar uh entitled, Mastering Orthopedic implants. This series is delivered to you by the Orthopedic Academy. Um And for, as a note, I'm the convenor of this decision. Today's session is about total knee replacement and I'm very pleased that we have with us, Mr A Kaur, he's a consultant orthopedic surgeon at Queen Elizabeth Hospital or at Queens Hospital in Fort. Uh as I said, his talk is about um the knee replacement implant. He will touch on the history biomechanics, biomaterials. Um That would be the main focus of this lecture. So the session will include first of all AAA lecture and followed by a set of multiple choice questions and you will all have an opportunity at the end to ask any questions. The teaching session is targeted at junior doctors level between foundation year to ST three. However, it will be very suitable as well to medical students and more senior trainees as well as other health professionals uh involved in trauma orthopedics. However, the the talk might not be absolutely spot on for each level because these levels are variable. So if anyone wants to find any concept a bit complicated, please get in touch and we will always try to explain further and if anyone else wants, you know, at a higher level, maybe senior trainee. Um uh we always uh we have a lot of other resources to prepare senior trainees for the orthopedic uh exams. So without further ado I will leave you now with the Mr A and while he's talking, I will, I will let you know on the chat session, please. First of all, remember to ask your questions. We encourage you to ask questions. Please write your question on the chat area or you can speak to Mr Kaul yourself if you raise your hand. Uh, but please don't leave the session today if you have any doubt about any of the discussed um uh topics or concepts. And um this series, this is one, the first one of seven webinar series and I will leave a link in the chart area of how you can book the future sessions. So without further a do back to you here and welcome and good evening, uh, good evening, uh Farra and thank you for that introduction and uh also to orthopedic Academy for uh, to giving me for giving me this opportunity. Uh It's uh and welcome all um uh listeners. Um, the topic of, uh, today's discussion is the evolution of TKR implant design and it's quite a vas topic. Um and we will try to uh summarize bullet points in some areas and go into a bit more detail uh in, in on how the knee implant has evolved over almost uh five decades, um 50 years of uh design changes. Uh and um uh I expect uh hopefully most of, you know what a basic total knee replacement is. Um It's basically got a, a femoral component which is metal and a tibial base plate which is metal and there is a polyethylene uh spacer. So that's the basic concept. And these metal uh implants are either cemented or uncemented, fixed to the bone, the lower end of the femur and the upper end of the tibia uh for a lament. Now, the use of total knee uh replacement in arthritis and other degenerative pathologies um as I said, has gone through five decades of uh development on my introduction slide on the left. You can see a very, very old, one of the first knee replacements were, which were built five decades ago and, and, and now where we are and where the future is on the right. So, um so that's what I wanted to introduce. And um basically the goals of uh a knee replacement, every surgeon or everybody in the industry or research uh are trying to achieve uh uh short term and longterm goals with a good design of a knee replacement. And the short term goals are to get a pain free functional knee which is stable and uh it can and reproduce the native knee kinematics um of a normal knee. And um in the long term, we want a good outcome, patient satisfaction as well as uh longevity of the knee implant replacement, uh or what is also known as survivorship. So, with that background, um let's see how it all started and um uh who are the pin ring surgeons. Um So, uh going back into the history, goes back, you know, in 18 60 when Ferguson, Doctor Ferguson performed a first time resection arthroplasty for arthritis of the knee. And this was followed in 18 63 by another doctor we Neil who uh started interposing uh tissues between the femur and the tibia. Uh the tissues included capsules, skin muscle fat, big bladder, pretty much anything they could find surgically. Uh They used to interpose between fever and tibia, but if these techniques fail to give any lasting pain control. So, um moving quite way forward. 1940 was the first time Doctor Campbell uh was the surgeon who did what is known as a hemiarthroplasty of the knee. Uh So he used the facial graft and um and, and, and this was from the successes uh uh of another surgeon uh Smith Petersons uh who was doing similar kind of uh facial grafts in the hip at that time. So Campbell basically performed a mold hemiarthroplasty of the knee by fitting metallic moles to the femoral condyles. And however, even this technique failed to give any successful pain relief to arthritis. Now, this technique was uh modified by Smith Peterson in the 19 forties and who added a stem to that metallic prosthesis of Campbell. And they showed some short-term success that was called the Massachusetts General Hospital, femoral condyle replacement. Now, during this time, in 1940 there was another two doctors, Doctor mckeever and doctor mcintosh, very again, pioneering surgeons in the arthroplasty who developed a vitali tibial hem arthroplasty. Uh However, unfortunately, that also was a failing. Uh mcintosh by the way, was also important to develop a lot of tools which are still used in instruments used in standard knee replacement surgeries. So he has credit to a lot of instrumentation. He was also the one who uh came up with the concept concept of creating flexion extension gaps and using spacers to measure them and to achieve ligament balance. In 1950 in a parallel level, a surgeon called walls shears attempted the first bi compartmental knee arthroplasty replacing both the femur and tibia artic surface together. And at that time, he used the hinge with the intramedullary stem that means a stem going into the femur and the tibia, the initial design had high stresses and high rates of loosening. And hence um another uh modification of that was developed by par with a new hinge which shifted the axis of the rotation slightly posteriorly. And we will see how that work, but that certainly was better than the um Wus Hinge. However, that also started to fail uh as a result of loosening uh due to complex rotation moments that happen in the knee. Uh we will understand that when we discuss the knee kinematics. So next one, in 1970 was really the time when things turning around in favor of nee arthroplasty development. The first design that lay foundation for current implants were developed at that time and at that time, uh the world was divide, orthopedic surgeons divide into two. basically school of thoughts and two theories started to develop. On one hand, was a anatomic theory and on the other hand, was a functional theory or an approach. So the difference between the anatomical and functional approach is an anatomical approach. Um Basically, you they were preserving the cruciate ligaments, both the anterior cruciate and the posterior cruciate and just doing a replacement of the condyles. And there were uh various pin ring surgeons as mentioned uh on the right uh who were following those and basically that carried on developing in the second generation of knee surgeries in the later seventies and early eighties in what is known as the modern L CS, a low contact stress uh prosthesis. On the other hand, was there were another group of surgeons who were generally taking a functional approach in which they were excising the cruciate ligaments and those were known as the total condylar prosthesis. Uh And um uh these were the two different things that were developing. So bear in mind these two approaches and we'll see how the implants develop from these two different approaches. Now, in the functional approach where they excising the AC and PC L, they did notice the first uh to, to total condylar pros prosthesis. They noticed that there was more anterior femoral translation happening and there was anterior tibial wear happening and this was modified by Insel Burstein. Uh another pin surgeon uh and he developed what is known as the total Condy, total condylar knee replacement. Uh Later on, these principles were adapted into developing a femoral post and C AM mechanism uh which again, we'll discuss in later, but that's how the two concepts started. So I'll, I'll leave this slide on because this is a very nice slide which shows the how on the top left, the anatomical uh pioneering surgeons who were of the anatomical philosophy were developing their knees. Uh And at the bottom is the functional group of people who are developing their knees. So you can see the name of the ping surgeons, as you see, er Coda Yamamoto uh was developing the Mark series. There was a geom medic knee coming which then became the Miller Galante knee. Townley was putting an atomic knee which then became cloudier and there was a poly centric knee which then became a Duo Condylar. But if you see this timeline from 19 seventies down to about 1978 uh if you see the functional group of designs have started to develop more. Uh and however, the anatomy designs have kind of stopped from 1974 and we'll see why. Uh so whilst this was happening, these two school of thoughts, there were other advances going on like the original uh high density plastic poly which was developed in 19 6 63. Also, uh bone cement metha methacrylate uh was approved for medical devices by the FD FDA in 1971. And all the uh advances in total hip arthroplasty uh by Doctor John Shaha. Uh all those principles and theories were being applied in knee replacement surgery as well. So if you again look at the uh timeline, we are around 1971 when there was a surgeon called Doctor Gunston. Uh he developed what is known as a poly centric knee. So he was trying to see more focus more on the kinematics and trying to find the center of axis of femoral rotation. And he felt that it the center of axis was not one, it was poly and and that's what he was trying to develop. And he actually studied with Doctor John Ley, uh the ing hip surgeon. So uh as I said, he, he believed that the knee kinematics do not occur in a single plane like a hinge rather than rather the femoral condyles roll and glide with a changing center of rotation throughout the arc of movement Uh So, uh this was the first design, the poly Andric knee that did not attempt to reconstruct the knee as a hinge, but rather attempted to preserve the knee anatomy, keeping the cruciate and collateral ligaments intact. The procedure resurfaced the femoral condyles and cemented separately, the Cobalt chrome semicircle implants using cement on the table side. The medial and lateral table compartments were also resurfaced and cemented in two concave polyethylene liners. Now, this became the standard anatomical design. Doctor Gunston s knee uh A as you see, another parallel uh anatomy design was by Coda and Yamamoto, which was a metal femoral implant with a single polyethylene mold for the table side that was minimally constrained and the difference was that it had a central cut out for the cruciate ligaments. So he understood that there will be impingement of the cruciate ligaments. So he made a cut out in the femoral implant. This mo implant was further modified as Mark one and Mark two and demonstrated fairly good survivorship at that time in the seventies. So this design by Doctor Townley was known as the total knee. Original. In this, the femoral implant had a decreasing radius of curvature at the back. So from front to back, the radius of curvature was gradually decreasing to encourage femoral rollback. Now, femoral rollback is a very important posterior femoral rollback is a very key concept in knee replacement and we'll talk a little bit more about it. But this is the time when people were try learning to understand that what exactly posterior femoral con uh rollback is. So, um so um in the same period in 1971 at Mayo Clinic, Doctor Coventry developed the geom medic knee right at the top left, which was again an ethical knee. And his tibial component was solid poly and it conformed very closely to the femoral component. It preserved the cruciate ligaments. However, because the uh very high conformity of the art geometry, in combination with the cruciate preservation, there was a k kinematic conflict and which led to early loosening and failure of the, the Geom knee. Zimmer later on tried to modify the ge geometric knee and came up with a Miller Galant knee replacement. And we also have a unicondylar uh knee replacement which is very successful in the USA uh of the same name by Zimmer. The next by Zimmer recently is also a variation of the geometric knee. So that's where it is inherited from now in the same period. In 1971 if you look at the bottom functional designs, there was a group of surgeons Michael Freeman and Swanson, professor of Michael Engineering. He developed the Freeman Swanson bi compartmental knee prostheses which indeed is truly the first or found or or the foundation of the current total knee replacements in both theory and in design in theory, the goal of the implant was to emphasize mechanical stability and prioritize the function over preservation of anatomy. So, Doctor Freeman recognized that many of the knees requiring arthroplasty had a significant angular deformity. So he decided that mechanical alignment was best achieved by sacrificing the cruciate ligaments. The implants are placed by for mechanical alignment, not anatomical alignment. Uh Furthermore, with the Freeman Swon knee, uh without the cruciate ligaments, the tibial eminence could not be, could be removed, offering multiple advantages instead of making small bone cuts to reproduce the complex knee anatomy, simple parallel bone cuts could be made to facilitate the surgery and its reproducibility. Ma Freeman also uh uh employed the Macintosh concept of spacer blocks for gap balancing of flexion extension gaps and uh uh that gave a a lot of uh stability and good kinematics. So, in Freeman's knee, there was no posterior rollback rather, it was called a roller and Trough design. The femoral component of the Freeman knee was made of Cobalt chrome and the tibial component was made of polyethylene. Uh At that time of the Freeman knee, 1970 there was only one implant size available and the patellofemoral joint was not addressed. So, in 1973 Freeman and Swanson uh modified uh their own knee and added an anterior flan to the femoral component and also a patella button to resurface the patella. This then uh became what is known as the IC LH. This was one of the uh best modification that Freeman Samil did. So again in 1971 a surgeon by the name of uh John Insel was working with Doctor Chiru Rao and Peter Walker at the hospital for special surgery to develop what is known as a total condylar knee. The first design of the total condylar knee was a duo condylar knee. Now, in contrast to the uh Freeman Swanson knee, the duo Contar knee was based on recreating knee anatomy and native kinematics by preserving the cruciate ligaments. In 1974. Uh The same designers ins so, Rava and Walker took some lessons from uh failures of duo condylar implant and focused their efforts on the alternate theory of design. So uh rather than making anatomical designs, they started uh picking up the good points from the functional uh group of surgeons and then they developed what is known as the PC or the total condylar prosthesis at the hospital of special a hospital of specialist surgery. This was also influenced strongly by the design of the IC LH. In the past, uh similar to the ICL, the cru shas were sacrificed in the total condylar knee and the femoral condyles were symmetric yet, unlike the ICL H, there was a more anatomy change in the radius of curvature posteriorly. So there were two radiuses, two rai, the posterior femoral radius was smaller than the anterior. Also, in addition, there was an anterior flange placed to help patella tracking. Uh however, the rest of the things remains the same, the tibial component was polyethylene. Uh And uh uh there was a small tibial eminence post as well. So this total condylar knee then went on to become what is now known as the cruciate sacrificing designs because cruciate were removed. However, at that time, there was no force to replace. In 1975 the total condylar two design came, uh it basically had some small differences. Uh However, instability still remained a problem And then doctor Ran wet, modified uh the total condylar two design and made the new prosthesis, which is now known as the Press Fit Condyle or the PFC or PFC SIGMA uh uh marketed by di um in 1974 there was another surgeon called Doctor F Thar, who was the first person to design a metal tibial base plate with a variable tibial poly insects. Now, this is different because when we saw when Freeman Swanson made his first uh knee replacement, he had only one size, but Doctor F Thar introduced this medial tibial placement with different poly sizes. Um There was other knees by Dr Papas and el uh which is known as the new Jersey knee, which then went on to uh be called as the low contact stress or the L CS design. Uh uh And in 1978 insult Burstein prosthesis uh was introduced the IV prosthesis uh which corrected most of the limitations of the previous total Condy prosthesis by creating the first posterior stabilized design. Now, this was a hallmark in the development of uh especially the posterior stabilized knees. And we will talk a little bit more about the post. What is the difference between cruciate retaining and posterior stabilized knees? In, in, in a, in a, in a few slides but insult bursting prosthesis was the first prosthesis. We designed the central C AM on the femur which engaged the back of the tibial post at 70 degrees of flexion and drove the contact point posteriorly during flexion to create the posterior femoral rollback that we knew existed uh a few years ago. However, we could not reproduce it uh by design and insult bursting was the first person to, to do, be able to do that. So that is how the various anatomical and functional designs developed between 1970 1978 there was a AAA huge amount of development and basically, in summary, they ended up with two groups now rather than the anatomical and functional designs. Now, we are uh in two different groups. One is known as the ps implants which is posterior stabilized. And on the right, then there were a group of implants which are called the cruciate retaining implies. So again, the left table shows you some of the uh uh uh knees which are PS implants and on the right, uh you have some other knees which are following the philosophy of cruciate retaining. Um at that same time, uh another co uh terminology uh coin for the posterior femoral condyle anatomical shape was the Jakov. And that is where the uh anterior part of the femur femur in a um in the sagittal plane. If you look at it, uh it has got a bigger radius of curvature. And posteriorly, there is a smaller radius of curvature uh to allow for the posterior femoral uh rollback. So um apart from these two basic designs, cru cruciate retaining and uh posterior stabiliz, there are a few other terminologies that we need to discuss uh and which were added into the development of the knee design. And uh the, the first one was uh the constraint, put, put into AAA knee implant. So the constraint means that the constraint prostheses are the models that can assure the best stability for the joint. And the stabilizing function is completely due to the prosthesis and not due to the ligaments uh among the different constraint processes, the hinge ones are able to self stabilize so they can be a hinge one or a, a non one, but the hinge ones are self stabilizing. Uh And um um Walde uh was the first one and followed by par who developed the hinge prosthesis. Now, uh these don't allow translation in uh media laterally, very minimal and very minimal rotational uh uh um freedom of movement. Uh And as a result of that, the, these implants cause a lot of high stresses on the bone and the bone cement interfaces and they can lead to early loosening and complications like fractures or dislocations. Um These, these are uh Romy walkers uh and uh kinematic rotating hinge and CCK are various different types of uh constrain prosthesis um developed by various surgeons uh uh during the development of this uh design. And on the right, you see uh some of the pictures uh of a uh hinged and a rotating platform on uh uh on on the screen. So, um by this time, uh late seventies and early eighties, um all tic a implants were basically divided into uh two or three categories. Two main categories were the first one was an unconstrained implant which has no constraint. And out of these two oo in this category were the two sub uh categories which we discussed. One was a cruciate retaining type and the other one was a cruciate sacrificing or the or, or the posterior stabilizer ones. The second uh category of implants are the constrained ones which we just saw saw could be hinged or non hinged. And as for the metal baseplate, the mo the bearing of the polyethylene or the spacer is usually fixed onto the metal base plate. However, there are some implants where the mobile, uh the bearing is mobile and is allowed to rotate and spin. Uh So generally speaking, t care design, any implant can be uh put into one of these three categories in terms of design right now as uh late seventies and early eighties, when, when the, when most of the surgeons agreed to these design philosophies, they started moving their attention more towards the actual kinematics of the the knee replacement uh to improve outcomes. Um Now, in terms of kinematics, as, as the knee replacements have developed over almost three generations, we're probably in the end of the third generation. Uh So was the kinematics developing as well. So, a good understanding of the kinetics is key to uh the design of the uh a knee replacement. Now, the knee is basically a modified hin joint and the knee movements happening are described as root translational. So the figure on the uh uh top left shows all the degrees of freedom and the knee has got six degrees of freedom, three degrees in rotation and three degrees in translation. Um And we have to uh uh be in bear in mind the axis of rotation, which is very important we'll talk about in a, in a bit. Um So the, the very early knee replacements, the kinematic philosophies around them uh in the first generation, uh were more uh propagated by AAA person called J o'connor who developed what is known as the four ba four bar link theory. Uh I'll take you to a picture and we'll come back. Uh So basically on the left, you see the surface of the femur condyle, the upper part of the tibial condyle and they're connected with a crosslinked, a anterior cruciate ligament and posterior cruciate ligament. So those are the four bars which are linked together. And he believed that at the point of intersection of the cruciate ligaments is where the center of axis of rotation is happening. And with, from extension to increasing to full flexion, uh there is a tendency of this intersection to move more posteriorly and also inferiorly. And this is what was the four Bartling theory uh uh propagated by uh o'connor. So, after the four bar link theory, if you see uh during the second generation of knee implants, they started looking at poly percent uh versus single axis of rotation. Uh uh and, and, and, and, and, and that was also a, a proposed theory. Uh and also uh they started uh studying anatomical studies of femoral condyle to understand the jake of the femoral component. Um The, the jaco of the femoral component means that the uh anterior part of the femoral condyle, distal femoral condyle has a got a bigger radius of curvature and the posterior is a, got a smaller uh curvature. And so they were changing, making changes in the design of the femoral implant to uh to, to match that there were three key points in the changing axis of rotation. This supported the posterior rollback of the femur and the four bar length theory. This, this philosophy led to the generation of news uh like vanguard journey to and persona all had these similar characteristics. So, whilst you are on uh posterior femoral roll back, uh let's, let's recap that again. Uh The drawing uh the picture on the right demonstrate the contact of the femur and the tibia, right in the middle, in full extension, the PC L is uh intact. And as the uh knee goes into more flexion, you can see that the point of contact to the femur and tibia goes posteriorly. Now, this happens when the PC L is present. However, if the PC L is absent in a uh either a na native knee or a knee replacement, you can see if in the absence of PC L, there will be no posterior femoral roll back. So, posterior translation of femur with progressive flexion improves the quadriceps function also and also the range of knee flexion by preventing posterior impingement during the flexion. And this is controlled by both the ACL and PCL. However, in most of the knee replacement, the ACL is sacrificed anyways. So that brings you to the two the two different uh designs which is PC L retaining and PCL substituting. So in PC L retaining, if you have the PC L like in the cruciate uh retaining uh implants, there will be some normal posterior displacement of the femoral condyle and um which is beneficial. However, uh as a as a uh disadvantage, sometimes you notice in the cruciate, there is a paradoxical anterior translation of the uh femur in the 1st 40 degrees of flexion. And this can be uh accommodated by putting anterior lips on the uh uh polythene uh spacer. In the PC substituting uh implants, there is a tibial post which as we discussed contacts the femoral cm in about 6 to 70 degrees of flexion which ends up in which leads to posterior displacement of femur reproducing the normal knee kinematics. So this is uh another diagram, 22 pictures to show exactly what we discussed. There is the post on the tibial uh polys spacer. There is the C AM and that gets in connection and leads to posterior frontal roll back. Um With cadaveric studies, people have the research have shown that uh the uh the exact area of the axis of central axis or rotation on the femoral condyle and it often matches exactly with the transepicondylar axis. There are other ways to find the axis of rotation uh like white side by drawing white side line which is uh uh uh uh uh goes to the center of the uh troch and the and the top end of the femoral notch, a line drawn through that and AAA line 90 degrees to that line will be the center of axis. Um Also by that, by the 19 seventies, there was uh more focus on the uh difference in the medial compartment, the lateral compartment. Whereas the medial compartment has a concave surface with a more or less stable position throughout range of movement of the femoral condyle. It's more fixed uh compared to the lateral compartment which has got a convex surface. And femur is not as fixed and it tends to rotate and roll backwards as the knee flexes. This is what these pictures demonstrate. This is uh just a picture to show again the more posterior femoral roll back and posterior contact and deeper uh flexion. Uh The picture on the left top shows the transcondylar axis to identify the uh uh center of a uh center of rotation. Um And uh some cadaveric pictures to show the same. Uh This reminds us of the uh very old previous four bar link theory on the left which we discussed already. Uh and how the AC L and PC A contribute to the knee kma kinematics. And the picture on the right shows how the uh radii of the anterior curvature is much more than the radial curvature, the posterior femoral uh Condy. The picture on the left again focuses on the development of implants with uh different radii. And the picture on the right uh is showing uh how the axis of rotation is uh dynamically changing uh from full extension to flexion. However, the average of all these axis in all range of movement usually coincides with the trans epicondylar axis. And hence, there is a consensus that that is the selected one. Oh after an understanding of all these uh previous uh anatomy and kinematics studies, there was a theory of a medial pivot knee kinematics, which essentially means that the medial compartment of the femoral condyle uh has got more rigidity. It, it, it, it, it it does not demonstrate much translation or rotation. And as as a result, um most of the uh spin is happening in the lateral compartment where the femur condyle is rotating and spinning and rolling backwards as you see in this picture, right? So that was uh about uh some key points about the kinematics. Um we have touched upon constraint, but we'll repeat that again. Uh Basically constraint is the design of the implant which gives you varus and valgus stability and flexion extension stability. Uh and is basically indicated where patients have got uh significant ligamentous laxity like either an MC L rupture or global ligamentous laxity or bone loss as a result of infection, previous tumor resection or other pathologies. Um in these kind of patients standard non constrained implants like the cruciate retaining or the sacrificing will not provide enough stability, just the cm and post will not be able to provide enough stability. And hence, we need constraint devices. Now, in order of a constraint, from least to most cruciate retaining has pretty much no constraint, posterior stabilized or cruciate sacrificing have got some more constraint. Um Varus valgus constraint, non hinged are furthermore constrained and the most constrained uh knee implants are the rotating hinge. So this is a uh uh a diagrammatic description uh pic digo representation of the increasing level of constraint from the bottom left where the crude retaining. And you can see the poly has got no post. As you go move forward, the polyethylene liner has got a post and there is a notch in the femoral uh implant to adjust for this along with the C AM and post mechanism. And as you go further and further, one could increase the stability uh and constraint um by increasing the size of the C AM and the post. But that just means that there will be more bone resection made and which is not helpful uh uh in, in in for future revision surgery. Uh And uh further, if you keep going on the right top uh and increase the uh constraint, we we end up with rotating hinge uh implants, right. So the next concept in knee design replacement design is what is known as modularity and basically uh augments added to a standard prosthesis or an implant to balance soft tissues and to restore wherever there is bone loss. Um They could be in the form of metal tibial base plates with modular quality inserts. However, they are quite expensive uh are much more expensive than all polyethylene tibial component. And we will talk about that all Lyn top tibial component, which is one of the cheapest versions of knee replacement. Um Putting augments has an equivalent rate of aseptic loosening compared with all poly tubing component. Uh you could use metal augmentation as seen in the picture on the right for bone losses. And you can make modular femoral and tibial steps. There are advantages uh because you you have an ability to customize implants in. However, there is disadvantages in putting modularity as that can increase the rates of osteolysis in modular component. They uh also been noticed backside poly wear uh because of the micromotion which occurs between the tibial brace plate and the under surface of the polyethylene insert. The next concept is the type of fixation. So generally speaking, the more popular uh are the cemented uh knee um standard implants as depicted on the right two x-rays A P and lateral. However, uh and they have proven survivorship and function and one can use high risks cost cement as it has got a longer working time useful for the surgery. However, there are cement versions of knee replacements with flanges and pegs and uh hydroxyapatite coating uh on both sides which uh which allows for longterm biological fixation. However, in the long term, um cemented have proven better than cement less now. Uh there is a variation in the mobile bearing uh and uh to put less stresses on the uh metal poly articulation and uh uh and to accommodate for the kineti kinematics, the bearing can be allowed to be mobile on the base plate. And these are known as mobile bearing knee replacements. The problem with these can be that uh they can be a mobile bearing spin out and they can uh sometimes dislocate. However, the advantage is that they will reduce uh poly bear uh debris. So again, let's go back to the main uh designs and summarize them. So we have a cruciate retaining design which is used indicated for people with arthritis with minimal bone loss, minimal soft tissue laxity and an intact PC L. They should be used in varus deformities are less than 10 degrees and valgus deformities are less than five degrees and x-rays won't show any box in the central portion of the femoral component. Uh vaso compared to the posterior stabiliz knees, which will show a box. The advantages of cruciate retaining design are that it avoids the tibial post cm impingement and dislocation that occurs on the P SPS knees. And it most more closely resembles the normal knee kinematics. There's less distal femur needs to be uh resected and it is good for revision surgeons if necessary. Uh Some believe that there is improved proprioception. However, that is uh uh uh debatable. Um There are new POLY options which can allow for PCE substitution via an daily stabilized knees or even ultra congruent shapes in cases of PCE insufficiency without loss of functional results. The disadvantages of cruciate retaining design is that the PCE may be tight, which may lead to accelerated Pothen wear um as well. So, on the picture on the right. These are some of the uh posterior stabilized knee implants, cruciate, retaining uh these increase the flexion gap in relation to the extension gap. AC AM is uh present as we discussed that engages the post during flexion. Uh poly polythene inserts could be uh more congruent or deeply dished. Mostly PS knees are used for indicated for patients who had uh previous patellectomy. If they have inflammatory arthritis, that rheuma like rheumatoid arthritis, which can lead to progressive uh disruption of the P cell insufficiency. Or if the PC L is actually deficient or absent. If you uh uh shown an x-ray of a cruciate, uh sacrificing knee or post stabilized knee, the lateral x-ray will show an outline of the C AM or the box. Uh The advantages of doing a PS knee is easier to balance the knee with absent PC L. And arguably you get more range of movement and the surgical exposure is easy. However, the disadvantages with uh these knees are that the C AM there could be ac AM jump. AC AM jump is a uh uh is a, is a complication where the cm uh and post dislocate uh uh with lo flexion gap in or in hyper section, the C AM can rotate over the post and dislocate and uh one has to do a close reduction. The other disadvantages of uh PS sneezes that can cause uh accelerated tibial posterior poly wear. Also, sometimes you can have what is known as patellar clung syndrome where the scar tissue uh in the anterior half a pad can get caught in the C AM post mechanism and may need arthroscopic resection. Um summarizing revising the constraint, nonhuman deep femoral box provided. Uh they provide sorry varus and valgus stability and rotation stability. Uh They're indicated in patients who have later collateral lain or deficiency or MC L LAIN deficiency when there is flexion gap laxity, or there is moderate bone loss in instead of in, in, in, in a setting of a neuropathic arthropathy uh like poliomyelitis. Um The advantages of constrained devices that they are providing stability in these deficiency of ligaments or bone loss. Uh However, there is a disadvantage that you have to do a lot of bone resection to be able to do that. Uh and a lot of stresses going on the bone, uh cement interface, implant, cement interface, uh and high, high uh evidence of a high um risk of uh future losing. Uh some of the uh types of constraint. Uh version of constrain on implants are the LCCK sigma TC three lesion, uh Vanguard ssk and triathlon. Then talking about the constraint or rotating hinge prosthesis here. The tibial bearing is rotating around the yolk on the tibial platform and hence, it's called the rotating hinge. This decreases, this decreases the constraint on the overall device and on the bone they should be used in global ligamentous deficiencies, hyperextension instability uh neuropathic joints pretty much the same indications but more serious uh uh laxity or deficiencies. Uh One is this is um more stability. However, the disadvantage, again, the same, the more the constraint, the more the stability, the more risks of stresses going on to the bones and the cement interfaces and higher the risk of aseptic closing. Some of the uh types of constrained rotating injury are the SROM nos next Gen Rhk or the OS S knee orthopedic salvage uh system. There are some minimally constrained rotating platforms as well where the uh polyethylene can rotate on the tibial baseplate. Uh PCL is removed at the time of surgery and these are are indicated more in young and active patients who are looking for more range of movement and better kinematics. Um It is arguable whether these are better in terms of outcome and theory, they reduce the poly where as the increases contact uh area is in increased and the uh the force on the uh poly thing is less the dis one. This the disadvantage is that there could be a mobile bearing spin out or a dislocation of the mobile bearing. Uh A word about highly congruent liners, um The liners poly lines made specially to match the medial compartment, con con cavity. And that allows uh the lateral compartment to translate between flexion extension, creating a medial pivot knee. Uh and uh and the P and the, and the, and the surgeons who believe in the medial pivot philosophy uh would uh vouch for this advantage is better knee kinematics. Uh However, in the long term, uh equate outcomes and survivorship have been seen in short term term. There is a variant of a tibial baseplate which is instead of having a medial tibial plate and a poly liner, they are all a block of single polyethylene. There is no clear indications. Uh However, the uh obvious advantages, they're less expensive and there is decreased rate of osteolysis. Uh as there is no uh junction between the uh metal and poly. Uh The disadvantage is that there is lose uh uh mo they lose modular flexibility. So you cannot put augments on the tibial side. And in the long term, uh even though they've shown decreased cost, the functional outcomes are equivalent. This is just a picture to show uh uh the spectrum uh from left to right. Uh In terms of constraint and various devices that we, we various uh categories of knee implants that we discussed again for revision on the left is the cruciate, retaining. The second one from the left is the posterior stabilizer with the CM and post. The third one and the fourth one are the uh hinge and the rotating platform. So there are some variations in the develop the T pr. There are some companies who made high flexion implants uh by doing design changes uh preferably for young and active sporting individuals. No special benefit seen uh and the outcomes. Then there are some patients specific uh implants, P SI where the cutting block instrument instrumentation is specially designed based on the CT imaging specific to the patient's anatomy. Uh It, it does take some time uh 2 to 3 weeks for the P SI implants to be uh uh delivered and uh manufactured and delivered. Uh However, at time of surgery, uh there is less instrumentation involved. Um no obvious cost benefit is achieved. Uh There is better post-operative alignment, uh uh sorry, no, no obvious cost benefit or uh uh outcome or alignment uh has been noticed with these. Um And uh there are some uh implants which are gender specific uh to address male and female uh difference in the anatomies as well. So um just recapping the concepts to remember, medial pivot knee kinematics uh measured resection and balance gap. Now, we didn't discuss much about measured resection and balance gap. Um because I think uh we might have to skip that because of lack of time. But in, in, in, in short, measured resection is when you are uh making femoral and tibial cuts based on the anatomy. Uh And then after the cuts, you're trying to balance the ligaments. However, balance gap uh uh technique is where you first focus on the flexion extension gaps and then confirm the uh femoral and tibial implants according to that future or well, current going on to future is mostly started with computer navigation where um um uh uh whi which has also uh been probably uh parallel and overtaken by robotic-assisted uh surgery. Um And uh Mao is uh uh the, the pioneer in robotic-assisted uh knee surgery and probably this is the future. Um If anything artificial intelligence might uh come in uh to add various uh uh surgical and design algorithms uh for uh implant, uh sizes or, or gap balancing, uh who knows? Right. So that's the end of my talk. Uh And thank you for listening. Um Thank you very much. This was wonderful. It's a massive topic and there are meetings that run on for days on, on aim to discuss this. Um So it's very difficult to summarize in, in a short lecture. But you did the excellent job of that. Uh Thank you. Thank you for going through the timeline. And it's interesting to see how the designs have developed from the initial hinge knee principle into more functional kinematic uh alignment principles in the condylar systems. Um And yeah, from that simple hinge knee one size knee now to this wonderful robots with the precise cuts and custom implants, patient specific implant, uh instrumentation and custom made implants. The designs have moved significantly over the last, you know, 30 40 years, isn't it? Um That was, that was excellent. Um M I think um as I said, each, each, each, each um principle and concept you discussed today is a huge lecture on its own, I think. Wonderful. Uh It's, there's a lot here actually to discuss today. The question is which one of the options is not a kinematics theory uh or philosophy that we discussed in total knee replacement? Is it medial pivot? Is it four bar link theory? Is it lateral pivot or is it axis of rotation is a term called cm jump? It is a known complication that we discussed in the lecture uh happens in which kind of uh knee prosthesis? Is it the cruciate retaining prosthesis? Is it the hinge rotating platform? Is it a cruciate sacrificing prostheses or it, does it happen with highly congruent liners PM jump? The last MC is that uh in a neuropathic joint like polym myelitis or patient who has significant neuromuscular weakness in the lower limb? Which is the knee replacement prosthesis of choice. Is it a all poly cement less implant? Is it a hinged or non hinged constrained implant? Is it a PC L cruciate retaining implant or is it a cruciate sacrificing correct answers? So, the first question about the theories, um all the other three are relevant theories of kinematics and there is no theory known as lateral pivot because we discussed that the medial side is the fixed side uh around which the lateral femoral condyle pivots. So it is called the medial pivot theory. So, therefore, lateral pivot theory is the wrong answer is the correct answer. But the wrong theory is no proposed uh second question C AM jump uh is uh depicted on the right um where there is flexion in stability and the C AM and post dislodge from each other. And, and this happens in uh the cruciate sacrificing or the posterior stabilized ps knee replacements. So, therefore, the third option is the correct answer. And the third MC Q uh was uh in terms of neuropathic joint, uh you would uh want maximum constraint for stability. Uh Otherwise the knee replacement will be unstable. And hence, for maximum constraint, we need uh hinged or non hinged constrained implants. So the second option was the correct answer for MC Q three, right? That's the end of my talk. That's perfect. Thank you very much, Mister Kapo. We are approaching eight o'clock now and I would like uh first of all to thank everyone who joined us uh this evening, I hope you all learned something I definitely learned a lot said uh recording will be available to you all um to watch again. Um I've shared on the chart the box a link where you can go to Earth Academy website and register for the future uh webinars of the series. So please join us. Uh or if you, if you register at least you can see the recording even if you're not able to attend in person. So I'd encourage you to do that. Um And I like to thank you uh Mister Kapo for the, you know, for joining uh taking office. Thank you for us for giving me this opportunity. I I must say preparing this lecture was uh a huge learning for me as well. So many things that you, you know, you, you miss and whilst you're preparing and reading, you learn these things. So thank you very much and thank you very much for the time and effort and everything you put into this uh lecture. And uh hopefully we will see you again in future sessions. So see you guys. Thank you for your time. Goodbye. Goodbye. Bye.