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Knee Mechanics related to Knee Replacement For Postgraduate Orthopaedic Exams
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Knee Mechanics related to Knee Replacement For Postgraduate Orthopaedic Exams
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Language: EN.
Segment:0 .
So, yeah, good evening, so thank you, everyone for coming in.
So we're very pleased to welcome Mr Wahid to basically chair this webinar for us, and he's going to be presenting on knee biomechanics relating to totally arthroplasty. And Mr Abdul is a consultant, orthopedic surgeon at the South Essex Foundation Trust and Nuffield health Brentwood hospital as well. And he specializes in hip and knee disorders during primary and as well as complex plastic surgery.
On top of that, he also does ACL reconstruction, arthroscopic knee surgery, including meniscus repair. And as well as ACL reconstruction, and his main research interest lies in rapid recovery program after joint replacement. So this is perfect webinar to highlight his knowledge to us. So welcome Mr Mr. Wyatt to give us a talk on the subject. Thank you. Thank you very much.
And I think today I'm going to speak about knee biomechanics as it relates to the knee of the plastic. It's a quite complex topic. And all of that and a lot of controversy is where we should cut the bone and how we should cut the bone. I'll try my best to make it as simple as possible, so at least you can understand and parse your own. So basically, what is the aim of total knee replacement?
For patient perspective, patient needs, pain control and patient needs, restoration of the function of the needs, the patient can have a normal knee function. But from our side, how can achieve that is basically we need to restore the neutral or mechanical alignment of the limb. We need to restore the joint lines. So the preserved ligament like medial ACL, LCL. And if we are preserving PCL, they function properly.
We need to have a balanced soft tissue envelope around the need, so there would be a correct flexion extension gaps. And last but not the least, we need to restore the normal view angle so the patient can have a normal kind of tracking before we go into details of our surgical cards. I think it would be nice to just review the anatomy of female tibia and the knee itself very quickly.
The FEMA has gone to mechanical authority to exercise one is called anatomical, which basically is literally biceps tenotomy tenodesis and all of the female. The mechanical access is actually passes through the center of the femoral head and the center of the knee or the center of the distal end of the female. So these two basically make.
Angle with each other of 5 to seven degrees, and this angle is called like a well, Wilgus angle, which basically the angle 5 or six degrees of the anatomical axilo of the female. So in Libya, the things are slightly simple, and the TBM and stomaco and mechanical exercises are actually the same. Intra operatively on the top and center of the ankle distally. So there are the mechanical excess of the limb itself, it's a line passes from the center of the federal health center of the knee and of course, center of the ankle joint.
So that's the mechanical excess, and that's literally very important for us to understand at this stage. So it will help us in future how we really need to make our surgical cuts. Knee actually makes about three to five degrees of physiological angle to the female if you remember your learning curve from pediatric knowledge. The child is born with like a badass knees as he grew up going to the welders and then stems back to 5 3 five degrees of the rest of the life.
The talk of the tibia basically is not like a flat. It has got three degrees, whereas that's a natural drop of material. So if with the anatomical or mechanical axilo because in tibia, they're the same. It makes a 3 degree of lettuce cut. So what is latest and what is? Well, we know that if the mechanical axilo of the limb passes media to the center of the knee is where whereas deformity, if it passes a letter to the center of the knee is, well, this deformity.
Why do we need to know about the anatomic and mechanical axes of the femur that's literally very, very important here for all of us to understand how we make our cars. Basically, where these two accesses the mechanical axilo of femur, which is yellow and the anatomical axilo drain, where the meat is slightly meat in the middle or slightly medial to the middle of the cochlea. This is the knowledge of the female, basically, that's the point where we pass over and like the family from the road.
That's our entry point. So that's we need to know exactly where the exits are. We use the female as a reference point. We usually put a thermal load inside, but we make a cut perpendicular to the mechanical axes of the female. So basically, we need to turn our J 5 to 7 degrees and Volker's so we can achieve this total small cut, which should be perpendicular to the mechanical axis of the female.
So that's why it's important. So this is called district workers cut angle, basically. So if somebody is very tall 5 feet, six feet, five inches or something, this is just really arbitrary. We might need to have a small angle if somebody short stature, we need to increase the angle. So when you do a distal cut angle, basically your femoral component will be facing towards the femoral head.
That's really very hard when you do the next time. Knee replacement, just have a look because it has to be mechanically neutral or perpendicular to the mechanical axis. Of the femur, not the anatomical. And that's where we want to achieve this, your new term. We need to restore the neutral mechanical axis of the limb by our cars or our tissue balancing. If the idea basically is that the load should transmit from medial and lateral side, equally, if it's a very Barrett's guess it can cause an excessive amount of load going on one side and it can cause where of the polyethylene.
So in alignment, if, as we know, the tibial the top end of the tibia has got three degree, whereas with the mechanical axis of the tibia. The proximal tibia, we normally cut 90 degree to the mechanical axis. How's everybody doing so, it actually takes more on the lateral and less on the medial side. We will come back in the next few slides. You will see how we make the cut at the moment.
This more important thing, which I need to really discuss, is the ligament benefit. This is extremely crucial, really for the success of knee replacement. If your soft tissue envelope around the knee medial that ligaments well. People can have instability and can cause pain and elevation of the prosthesis. We know that the osteoarthritis can cause scarring of the ligaments.
Ligaments can be contracted on one side can be attenuated. So we need to have a balancing of the need in both personnel as well as the surgical plans. So in Corona plain, we know the deformity is a virus or, well, guess. In various deformity, obviously, the medial side of the medial side of the knee, the structures will be contracted. We have more scarring on the left side.
They will be attenuated and stretched. There might be a bone loss on the medial side because of the weight of the bone. So how you achieve how you actually basically do the releases on the medial side to align your limb, always start for the simple things that take the positive first, then the deep potential. And don't forget, then see how the attach to the medial meniscus.
So when you're taking the meniscus, be careful. Don't take themselves with it. And if that helps you, that's fine. Otherwise, you might need to go to the post medial aspect of the need to leave the capsule and maybe send remembrances attending, send remembrances, then attaches to the post medial aspect of the knee of the tibia cemetery or semi nodes is actually part of the person's sweetness.
But it. The inconsolably and other deformities of vulgar deformity, which basically is the contemporary, is on the lateral side and it's convex on the medial side. So whenever you're doing this kind of Giants always, always examine the competency of the seal, the deal has to be competent, then you can do a very simple primary. Otherwise you might need to do a bit more constrained prostheses.
So similarly, in the natural side, start with the simple like taking those little capsules in your tibial band, maybe completely extending my need to replace it. And lastly, the lateral collateral ligament, if you release it, that would naturally come and do something like a or steel from the same femoral side. And don't try to detach. If some people there's a lot of education, you do advocate about the detach and put a screw here.
If you do that, best do constraint need. So sagittal plane balancing, which actually is the flexion extension of grab, it has to be symmetrical and equal, just a little give you an idea. The technique I'm discussing is called mechanical alignment technique. They are kinematic alignment technique, which we might touch upon at the end if you have a time.
The what we're saying is that what other cuts we are doing or I'm talking about is called mechanical alignment techniques to do the knee replacement. Right? so in flexion extension, a dumbbell flexion extension gap. The collection gap basically depends upon the Australian femoral court tibial guard and the PCL. If the picture here is very tight, it can really affect your collection gap.
Why do we need some ethical gaffes, basically, is that they give you smooth range of movement and stability to your joint and the longevity of the profits, that depends on these things and better believe it. The said the other gap is the extension gap, which actually it depends on the distal femoral cut tibial cord and posterior capsule. The capsule is very tight, and that can cause a flexion problem there.
We know that if your problem in symmetrical. Both flexion and extension, you need to adjust the tibia first. If the problem is asymmetrical, the gap flexion gap is different than the extension gap, then adjust the femur first. There are quite a few scenarios, and they are all given in. Various books have been given in the middle as well if the typekit extension tightens flexion. You didn't cut the enough tibia, so cut the tibia a bit more, and that really will resolve the problem.
Similarly, if it's loose and extension and lose flexion, probably we have got too much tibia. So they use thicker polyethylene insert or metallic tibial arguments. This is very little in primary setting. You really see people using the tibial arguments. Most of the time, you can get away with using thicker polyethylene himself. If your extension is good, but the lose and flexion, this asymmetric gap and we probably have got too much of the back of the femur, either you increase the femoral component or translate entirely, but clearly it's not easy to translate really literally most of the time you can get away by using a smaller size of the femur.
If it's tight an extension, but flexion is good. It could be the reason that the posterior capsule is still very tight, you have to release it properly. We didn't cut the distancing properly. I just released the capsule and see if that helps take off the distal. Is FEMA want to do extra? It is this extension is good, but slight inflection again. We didn't cut stillborn.
The official is probably very much scarred or there's no perfidious slope and the tibia. So you start one by one do with a little bit of the skull from the femur that might help you. Or you can, depending on the size of the femur. Similar loose and extension flexion is good. Again, it's a symmetrical cut. Too much of this femur, or there's a pea size is too big. Either you do distal augmentation or protective polyethylene insert and then readjust as if there's a tight flexion gap.
So what next actually is very important aspect of a knee replacement, whether we should retain the PCL or we should sacrifice the vehicle. There's a lot of literature in favor of both. And a lot of studies in favor in terms of the survivorship in terms of the functional outcome, I think there's not much difference in terms of long term the outcome of these.
The reprocessing, however, we can have a little I mean, discussion only if we retain PCL, the advantages are that probably there's more art of motion. There's intact PCM obviously prevent subluxation of the tibia. And there's a federal rollback, the federal rollback, basically, if you look at the picture as a knee flexes, the contact point between femur and tibia moves backward.
If you go along with so that's a similar roll back. PCB retaining does help. This one, but you probably need flatter kind of polyethylene tray to achieve that. The other benefits, I mean, there's less chances of election instability. It's really questionable, and stability isn't the female. This does not jump into idiocy because the piece here is intact.
Proprioception is better, probably. And what are the disadvantages rollback actually is the really rollback in PCL, retaining the rollback needs both ACL and PCL intact. In reality, when we retain PKL, there's the rollback as well as is sliding as well. So it's a combination of two movements, but you need to have a proper rollback. You need a flatter like a flat polyethylene.
But that's really very detrimental because flat polyethylene have a contact point and this strategy will be very high. And the rapid polyethylene where. So to combat that, we normally use program polyethylene. But it does give little roll back. It does provide and it's definitely congruent. Polyethylene reduces the stresses because the surface area of contact is lower and the stresses will be less.
Axilo substituting. Yes, it has got its own benefits. This is the Cam. Actually, it articulates with the post and it accepts like kind of PCL basically. So there are a few areas where people actually advocate strongly that we should use the PCL substituting be self-sacrificing implant, like if there's a previous slide to me, there's a potential risk of instability because the sense that week, if you remember that better, let me.
And in fact, let me record this attempt to exert about 30% extra force to achieve the same amount of work or achieve the same amount of movement. So the inflammatory property like rheumatoid or psoriatic arthritis. People said that they can cause later on PCP rupture because of the inflammatory process. And you should use PCP. However, there's a lot of disparity in literature.
People still sometimes use the PCL entertaining. So if there's a deficient or absent PCL, yes, you can use that PCL substituting. The advantages are probably maybe easy to balance with this absent PCL. Arguably, they say there's a more range of motion, whether it is true or not. There's a lot of debate on it. Easy, easy surgical experience.
The disadvantage? You need to be very careful. You need to be very careful and balance in either case, whether it's a little TLC or yes, in both cases, but in the field substituting. If your knee is loose and flexion, there can be a Cam jump. I can give you a little more explanation here. If this if the flexion is loose here, it will be.
Femur will jump over the post and it'll happen like that. And that would be your rays. So that's a ganjam that's one of the complications in the PCL substituting the other complication, which is quite common, is the perennial trunk syndrome. Basically, what happens when you're replacing the patella? The soft tissue is formed on the superior wall of the patella under the gold standard. And that scar tissue becomes like quite big thick nodule and clunk over the edge of the box of the knowledge of the femoral component.
It can be painful, or it can be very nuisance for the patient. Every time a patient moves about 45 40 degrees extension, they feel very like a slip in the knee. If there's not much symptoms, leave it, if it's really symptomatic, then you might need to go out and take exception of. So, no, actually, I will go into the details about the cuts, how we make it if you understand the formal articulation.
The most common problem in the replacement is the male checking of the patella, and the most common reason probably is the female internal rotation. But thankfully, the we know that you angle it from that line drawn from the anterior Alex point in the middle of the patella, from middle of the patella to the table. It's a mate of the guys by definition, not the speedy ball of the pedal.
Some of them are quite fussy. So the angle basically is literally very important to be maintained. It's higher in females less than males, about 30 degrees and female and male and about 18 degrees in females. So these are the different muscles acting on the patella, whilst the medial oblique, as well as the medial and the resultant vector, they're actually pulling up straight.
That's why the patella is actually kept in properly. So increase the acute angle basically is associated with the lateral subluxation of the teller. So our goal is to achieve a normal given angle. So how we can achieve that or how we can prevent abnormal attacking? On female side, we need to avoid female component internally rotation, so do not put several components internally rotated, do not media like the female component either put the female component neutral or externally rotated.
Or put the family component in the center of the digital single or slightly larger. How can we achieve that while we're operating the different landmarks which are available to us to use to actually make our cars properly? The apex isn't the same. Epicondyle and epicondyle access will go one by one. If you look at the picture on the top, that's the apex, which passes from the deep part of the truck up to the noj.
It's also called Whiteside line, your interior and bas status car should be perpendicular to this axis. Then come the epicondyle elections, which are concerns across the two medial and lateral epicondyle, which are easily palpable in primary knee replacement, your cards and interior and the posterior should be parallel to this one. The third one is the posterior epicondyle axis, which actually runs posterior part, your interior and gut should be treated externally rotated to this line, which axis we commonly use.
It's very important we commonly use the posterior axis because that's where the jigs actually the feet of the jigs rest on. And then from there we make our own adjustments. So that's why in most of the processes, we externally rotate three to five degrees. So coming back to the female criminal college, we know the medial female epicondyle is actually slightly larger, larger and extends distally as compared to the lateral side.
And the top end of the tibia makes a 3 degree virus cut here, so we cut the tibia perpendicular to the anatomical or mechanical axilo the tibia, which is the same. By doing so, we're cutting more on the lateral side that's on the medial side. But the federal side, we need to cut. Perpendicular to the mechanical axis, which was coming from the femoral head to the center of the distal femur.
By doing so, we got more on the medial and less from the lectern and resultant will be a rectangular extension gap. That's what we need to match that we need. Similar rectangular flexion gap as well. How we can do it. You need externally rotate your game 3 degrees because you are taking the posterior reference wheel. We will discuss in a minute and Australia, we're using this as a reference to see epicondyle.
We have a feed of the G8, so we sternly rotate so that will cut more on the medial less than the lateral procedure. There are few designs which actually have got a trapezoidal selection gap, which is to a few members there, but that's a different philosophy. We will have, we can discuss later on. So the idea is that we should have rectangular selection as well as extension gaps, and they should be symmetrical and equal.
It on the table side, but what we can do to prevent the ephemeral tracking. The tibial component, the center of that should lie at the junction of medial 3 and lateral 2/3 of the tibial tubercle. If you internally rotate the tibial component, when you extend the knee, the knee will externally rotate and the tibial tubercle will go laterally and it will increase the angle and will actually cause a subluxation of the patella.
So people component media one third and led to the third of the TV worker. Resurfacing patella always put patella media. It helps the right avoiding what I love about how which which can cause. But the problem with the selection.
So next, what's the fencing technique we should use anterior or posterior? Doesn't it make any difference? Whatever you do, the idea is to achieve the correct rotation of the family component and the size of the family component. I can tell you one thing is important. I mean, they have a lot of matters of doing interior referencing, policy addressing, referencing.
There's no right and wrong. I always do policy referencing my many colleagues do interior as well. But at the end of the day, you need to achieve proper sizing and the rotation of the federal government. And I wrote, as I can read, if your when you are doing the femoral sizing, if your thighs. Matches like with the AP damage, especially with the component like, say, the size 5.
Then doesn't it matter, you use a tuberosity referencing you're getting the same amount, anteriorly and posteriorly over the film, if you're the measuring measurement matches with the component available. However, if they be damaged, ulnar nerve famous family epicondyle in between the sizes between 4 and 5. Then you think different referencing will cause a different will cut the different amount of bone anteriorly and posterior?
It all depends which referencing techniques you use. So if I. If you have got. For example, 4 and 5. OK and you want to use the size you decided to use file size 5. If when you made it your file sizes between 4 and five, the posterior referencing you will cut same amount always.
In the pursuit of justice referencing it, the same amount will be called Australian. In Brazil referencing, if you're using side 5g, your profits will be very prominent here, will be lifted of the femur and you will stuff that family joint. But if you use side for industrial fencing, you still will be getting the same amount of yearly up here. But the interior it can cause energy.
You understand this is very important. Similarly, if you're using a referencing. And if you use file size five, the anteriorly, it will lie quite nicely with the female in India referencing whatever size you use, you're getting the same amount a It's a posterior which you got more or less. But if you use size 5. In India referencing, you've got whatever amount has been cut, it will nicely flush with the fame, the stadium, you will go to a little and there will be tight selection gap.
On the other hand, if you use smaller size. A the same amount of bone is gut, however, for in you will cost too much of bone like appear the deadline. And there can be a flexion gap in stability. So these two techniques, they're very, very important to understand. It doesn't matter whichever technique to use. And with the interior lieutenant, single posted, referencing the idea that you should have chosen appropriate size and accurate rotational alignment of the femoral component, that's literally the key here message.
If there's any male rotated femoral components, they'll have a poor gender checking. They can have any pain. Lots of motion loss function and implant implant can fail. So any designs, I mean, there is quite this really needs is by its own, it's really a full topic. But I can just little go through with the unconstrained and constrained unconstrained. Is that retaining and substituting constraint 1 is hinged on heat.
It can be fixed versus mobile bearing. It leads really itself. Have separate lectures. So there are different methods of doing the balancing or doing the cutting in the pool. In majority of the cases, we do mechanically aligned techniques with military dissection. Most of the people do this. However, some people use gap balancing the techniques.
So far, we have used using the AP axilo, the female trans epicondyle index of the femur and the posterior legs of the femur that actually is called manier. The dissection technique you measured with the jigs and you know where you put it and you know how much external rotation you want to actually create inside. So you actually from the jig, you do yourself. That's why it's going to make the reception technique in depth, balancing you balance the ligaments release.
Do the releases do the tibial cut first? Then you put a jig inside and put a femoral inside as well as differentiate. Then you bring the knee to 90 degree. Whatever the femoral component rotates externally, whatever the degrees, you fix it and then cut it. That's called gap balancing. We are a consultant doing hips and knees. One does get gave balancing on the sole mate.
There's no right or wrong. Both techniques are good. So in summary. What we need to achieve. We need to achieve the patient should be pain free and patient, should have the restoration of the function of the knee. Well, how can we achieve that? Basically, we need to achieve the proper anatomy and the ligament tension in the knee of.
So there were a few other actually I didn't really. I think she needs again a separate lecture computer assisted surgery, robotics, virtual reality software, pressure sensors and all these things they need to have, like separate. I just put that they should know that there are a few other things in the new placement as well. Now come the questions, and I think Justin probably have done it.
So I'm ready to go through it with you, with the ball and also the questions if you like to. Yeah, I think so, we go through the questions now, so I would appreciate if everybody can go through and the questions that now turn up in front of you. And then just answer as soon as you can, which of the following defines the mechanical acts of normally aligned limp.
The I think the most of them, the correct, the vertical line drawn from the femoral head through the center of the knee down to the center of the ankle. So majority are correct. The second one, performing a knee of the knee is stable and full extension, but it will not flex beyond 90 degrees and flexion is tied. Which of the following adjustment can achieve satisfactory range of motion and stability in flexion and extension?
I think all 82% said downsizing the femoral component, which I think is correct. The next is during the trial, the reduction in care or the surgeon was unable to fully extend the knee and the tibial tray lifts off when the knee is flexed past 90 degrees. What technique should be taken to obtain a balanced knee in flexion and extension to more proximal tibia?
I think that's correct. And the 66% right? They're in totally outclassed and excessive posterior femoral resection will lead to which of the following situation. Blues collection gap, yes, 91% The answers quickly during trialing in primarily are totally out last, the need does not extend into full, but flexion gap is nicely balanced after appropriate soft tissue releases have been performed.
What is the next most suitable step to balance the joint? He would have done. The second is female, 10, 73% people on Sunday, and I think that's correct. London, most of them has been clarified during your lecture, so there were questions about gap balancing versus measured reflection. I think you've explained it quite well in the candidates. Quite happy from that point of view as certainly, I think the next question.
Sorry, I lost it now. So so there was a question from Mr. ulnar nerve, who talks about where the trial's been inserted into the knee and the knee stabling extension, but inflection. The medial part feels a bit tight more than lateral, and the public doesn't seem to fit in the Mediasite. I guess it must be to do with his personal experience. It seems very, very specific about his question.
It's asking what to do next. I think the media side is tight to. They're probably the few things which can happen. Either the media releases are not sufficient that they need to address if they're too fast. So take them down. And maybe you cut more into bogus tibial cut. So you have to relook at that and see if your cut is correct, really.
Because if you tibial cut is like in guess, you cut more on the lateral less than the medium that can cause of this problem. So there are multiple really things that you need to look into. There's not one single thing I agree. I think I think also, if you are thinking about it being balanced with expansion, perhaps you need to be concerned that maybe your femur is in internal rotation as well, which is why on slap your media site tighter.
So certainly, I think you just have to relook at all your rotation and make sure that's correct as well. So and I think there is another question. This question for Mr. godsey, who is talking about roll back phenomenon. So he's asking about is the rolling back of normal phenomenon that you need to achieve with the implants or you need to avoid?
What is this significant? Yeah, this is all back in normal knee. When there's an ACL intact, that's a normal phenomenon. That's your physiological like something which happens in the knee. When we do knee replacement, the modern one, we sacrifice one or the bolt is, you know, the PCL in ACL when you sacrifice ACL, which we normally do see like training.
So in that case, it's not a true roll back. But yes, it does cause some sort of roll back because the hinge one hinge and the back is intact, which is BCL. It does actually force the femur to roll back. But as I said in my talk, it's not 100% true roll back. There's also some slide as well with it. So to have a pure roll back phenomena, you need a flat polyethylene, which we can't afford that will be very unstable.
We need Congress always even see our views congruent polyethylene, which basically the flat surface can cause contact point contact and can cause joint loading, which is more stress on one point and can cause a rapid failure. So it's a little compromise in both. Yes, we aim to achieve rollback, but not 100% Yeah, I think that's correct. So and so one final question is, I guess, the answer, probably, Yeah.
So does the previous look of fact gap balancing Mr. Nash is thus does the tibia slope affect cap balancing? Basically in when you get balancing, you're using basically first you release your soft tissue, do the tibial cut as you need to do three three degree or seven degrees to three slope, which I will implant. You're using the prostheses in general, you'll use three in next use.
Seven it depends really how much? If it is too much, obviously still slow, you balancing will definitely be affected. OK so you have to be really have to be like a balancing both sides. You can't really have too much slope with a view to have achieved more flexion. You need to keep with your prosthesis. You're using in a way that you can achieve the balancing in the soft tissue.
So when you've done that, you put in then femoral component. Wherever it goes, it will go out of your control. So it moves with the tibial chip. And that way you fix the components femoral and then you dissect it. I think that's I think the most important is to get the posterior still correct, isn't it? Yes, absolutely. And so I think there's a couple of more questions, but I think we've probably got to start doing the Viva session.
And I guess we will so we can try and answer it on a chat function. I don't know what you think of it for time purposes. We can answer them for the chat function. Yes no problem. Let you take over the screen and just do. We've got three volunteers. fact, we've got four volunteers today, but I think we've got time for 3 and we'll let the first one.
Segment:0 .
So, yeah, good evening, so thank you, everyone for coming in.
So we're very pleased to welcome Mr Wahid to basically chair this webinar for us, and he's going to be presenting on knee biomechanics relating to totally arthroplasty. And Mr Abdul is a consultant, orthopedic surgeon at the South Essex Foundation Trust and Nuffield health Brentwood hospital as well. And he specializes in hip and knee disorders during primary and as well as complex plastic surgery.
On top of that, he also does ACL reconstruction, arthroscopic knee surgery, including meniscus repair. And as well as ACL reconstruction, and his main research interest lies in rapid recovery program after joint replacement. So this is perfect webinar to highlight his knowledge to us. So welcome Mr Mr. Wyatt to give us a talk on the subject. Thank you. Thank you very much.
And I think today I'm going to speak about knee biomechanics as it relates to the knee of the plastic. It's a quite complex topic. And all of that and a lot of controversy is where we should cut the bone and how we should cut the bone. I'll try my best to make it as simple as possible, so at least you can understand and parse your own. So basically, what is the aim of total knee replacement?
For patient perspective, patient needs, pain control and patient needs, restoration of the function of the needs, the patient can have a normal knee function. But from our side, how can achieve that is basically we need to restore the neutral or mechanical alignment of the limb. We need to restore the joint lines. So the preserved ligament like medial ACL, LCL. And if we are preserving PCL, they function properly.
We need to have a balanced soft tissue envelope around the need, so there would be a correct flexion extension gaps. And last but not the least, we need to restore the normal view angle so the patient can have a normal kind of tracking before we go into details of our surgical cards. I think it would be nice to just review the anatomy of female tibia and the knee itself very quickly.
The FEMA has gone to mechanical authority to exercise one is called anatomical, which basically is literally biceps tenotomy tenodesis and all of the female. The mechanical access is actually passes through the center of the femoral head and the center of the knee or the center of the distal end of the female. So these two basically make.
Angle with each other of 5 to seven degrees, and this angle is called like a well, Wilgus angle, which basically the angle 5 or six degrees of the anatomical axilo of the female. So in Libya, the things are slightly simple, and the TBM and stomaco and mechanical exercises are actually the same. Intra operatively on the top and center of the ankle distally. So there are the mechanical excess of the limb itself, it's a line passes from the center of the federal health center of the knee and of course, center of the ankle joint.
So that's the mechanical excess, and that's literally very important for us to understand at this stage. So it will help us in future how we really need to make our surgical cuts. Knee actually makes about three to five degrees of physiological angle to the female if you remember your learning curve from pediatric knowledge. The child is born with like a badass knees as he grew up going to the welders and then stems back to 5 3 five degrees of the rest of the life.
The talk of the tibia basically is not like a flat. It has got three degrees, whereas that's a natural drop of material. So if with the anatomical or mechanical axilo because in tibia, they're the same. It makes a 3 degree of lettuce cut. So what is latest and what is? Well, we know that if the mechanical axilo of the limb passes media to the center of the knee is where whereas deformity, if it passes a letter to the center of the knee is, well, this deformity.
Why do we need to know about the anatomic and mechanical axes of the femur that's literally very, very important here for all of us to understand how we make our cars. Basically, where these two accesses the mechanical axilo of femur, which is yellow and the anatomical axilo drain, where the meat is slightly meat in the middle or slightly medial to the middle of the cochlea. This is the knowledge of the female, basically, that's the point where we pass over and like the family from the road.
That's our entry point. So that's we need to know exactly where the exits are. We use the female as a reference point. We usually put a thermal load inside, but we make a cut perpendicular to the mechanical axes of the female. So basically, we need to turn our J 5 to 7 degrees and Volker's so we can achieve this total small cut, which should be perpendicular to the mechanical axis of the female.
So that's why it's important. So this is called district workers cut angle, basically. So if somebody is very tall 5 feet, six feet, five inches or something, this is just really arbitrary. We might need to have a small angle if somebody short stature, we need to increase the angle. So when you do a distal cut angle, basically your femoral component will be facing towards the femoral head.
That's really very hard when you do the next time. Knee replacement, just have a look because it has to be mechanically neutral or perpendicular to the mechanical axis. Of the femur, not the anatomical. And that's where we want to achieve this, your new term. We need to restore the neutral mechanical axis of the limb by our cars or our tissue balancing. If the idea basically is that the load should transmit from medial and lateral side, equally, if it's a very Barrett's guess it can cause an excessive amount of load going on one side and it can cause where of the polyethylene.
So in alignment, if, as we know, the tibial the top end of the tibia has got three degree, whereas with the mechanical axis of the tibia. The proximal tibia, we normally cut 90 degree to the mechanical axis. How's everybody doing so, it actually takes more on the lateral and less on the medial side. We will come back in the next few slides. You will see how we make the cut at the moment.
This more important thing, which I need to really discuss, is the ligament benefit. This is extremely crucial, really for the success of knee replacement. If your soft tissue envelope around the knee medial that ligaments well. People can have instability and can cause pain and elevation of the prosthesis. We know that the osteoarthritis can cause scarring of the ligaments.
Ligaments can be contracted on one side can be attenuated. So we need to have a balancing of the need in both personnel as well as the surgical plans. So in Corona plain, we know the deformity is a virus or, well, guess. In various deformity, obviously, the medial side of the medial side of the knee, the structures will be contracted. We have more scarring on the left side.
They will be attenuated and stretched. There might be a bone loss on the medial side because of the weight of the bone. So how you achieve how you actually basically do the releases on the medial side to align your limb, always start for the simple things that take the positive first, then the deep potential. And don't forget, then see how the attach to the medial meniscus.
So when you're taking the meniscus, be careful. Don't take themselves with it. And if that helps you, that's fine. Otherwise, you might need to go to the post medial aspect of the need to leave the capsule and maybe send remembrances attending, send remembrances, then attaches to the post medial aspect of the knee of the tibia cemetery or semi nodes is actually part of the person's sweetness.
But it. The inconsolably and other deformities of vulgar deformity, which basically is the contemporary, is on the lateral side and it's convex on the medial side. So whenever you're doing this kind of Giants always, always examine the competency of the seal, the deal has to be competent, then you can do a very simple primary. Otherwise you might need to do a bit more constrained prostheses.
So similarly, in the natural side, start with the simple like taking those little capsules in your tibial band, maybe completely extending my need to replace it. And lastly, the lateral collateral ligament, if you release it, that would naturally come and do something like a or steel from the same femoral side. And don't try to detach. If some people there's a lot of education, you do advocate about the detach and put a screw here.
If you do that, best do constraint need. So sagittal plane balancing, which actually is the flexion extension of grab, it has to be symmetrical and equal, just a little give you an idea. The technique I'm discussing is called mechanical alignment technique. They are kinematic alignment technique, which we might touch upon at the end if you have a time.
The what we're saying is that what other cuts we are doing or I'm talking about is called mechanical alignment techniques to do the knee replacement. Right? so in flexion extension, a dumbbell flexion extension gap. The collection gap basically depends upon the Australian femoral court tibial guard and the PCL. If the picture here is very tight, it can really affect your collection gap.
Why do we need some ethical gaffes, basically, is that they give you smooth range of movement and stability to your joint and the longevity of the profits, that depends on these things and better believe it. The said the other gap is the extension gap, which actually it depends on the distal femoral cut tibial cord and posterior capsule. The capsule is very tight, and that can cause a flexion problem there.
We know that if your problem in symmetrical. Both flexion and extension, you need to adjust the tibia first. If the problem is asymmetrical, the gap flexion gap is different than the extension gap, then adjust the femur first. There are quite a few scenarios, and they are all given in. Various books have been given in the middle as well if the typekit extension tightens flexion. You didn't cut the enough tibia, so cut the tibia a bit more, and that really will resolve the problem.
Similarly, if it's loose and extension and lose flexion, probably we have got too much tibia. So they use thicker polyethylene insert or metallic tibial arguments. This is very little in primary setting. You really see people using the tibial arguments. Most of the time, you can get away with using thicker polyethylene himself. If your extension is good, but the lose and flexion, this asymmetric gap and we probably have got too much of the back of the femur, either you increase the femoral component or translate entirely, but clearly it's not easy to translate really literally most of the time you can get away by using a smaller size of the femur.
If it's tight an extension, but flexion is good. It could be the reason that the posterior capsule is still very tight, you have to release it properly. We didn't cut the distancing properly. I just released the capsule and see if that helps take off the distal. Is FEMA want to do extra? It is this extension is good, but slight inflection again. We didn't cut stillborn.
The official is probably very much scarred or there's no perfidious slope and the tibia. So you start one by one do with a little bit of the skull from the femur that might help you. Or you can, depending on the size of the femur. Similar loose and extension flexion is good. Again, it's a symmetrical cut. Too much of this femur, or there's a pea size is too big. Either you do distal augmentation or protective polyethylene insert and then readjust as if there's a tight flexion gap.
So what next actually is very important aspect of a knee replacement, whether we should retain the PCL or we should sacrifice the vehicle. There's a lot of literature in favor of both. And a lot of studies in favor in terms of the survivorship in terms of the functional outcome, I think there's not much difference in terms of long term the outcome of these.
The reprocessing, however, we can have a little I mean, discussion only if we retain PCL, the advantages are that probably there's more art of motion. There's intact PCM obviously prevent subluxation of the tibia. And there's a federal rollback, the federal rollback, basically, if you look at the picture as a knee flexes, the contact point between femur and tibia moves backward.
If you go along with so that's a similar roll back. PCB retaining does help. This one, but you probably need flatter kind of polyethylene tray to achieve that. The other benefits, I mean, there's less chances of election instability. It's really questionable, and stability isn't the female. This does not jump into idiocy because the piece here is intact.
Proprioception is better, probably. And what are the disadvantages rollback actually is the really rollback in PCL, retaining the rollback needs both ACL and PCL intact. In reality, when we retain PKL, there's the rollback as well as is sliding as well. So it's a combination of two movements, but you need to have a proper rollback. You need a flatter like a flat polyethylene.
But that's really very detrimental because flat polyethylene have a contact point and this strategy will be very high. And the rapid polyethylene where. So to combat that, we normally use program polyethylene. But it does give little roll back. It does provide and it's definitely congruent. Polyethylene reduces the stresses because the surface area of contact is lower and the stresses will be less.
Axilo substituting. Yes, it has got its own benefits. This is the Cam. Actually, it articulates with the post and it accepts like kind of PCL basically. So there are a few areas where people actually advocate strongly that we should use the PCL substituting be self-sacrificing implant, like if there's a previous slide to me, there's a potential risk of instability because the sense that week, if you remember that better, let me.
And in fact, let me record this attempt to exert about 30% extra force to achieve the same amount of work or achieve the same amount of movement. So the inflammatory property like rheumatoid or psoriatic arthritis. People said that they can cause later on PCP rupture because of the inflammatory process. And you should use PCP. However, there's a lot of disparity in literature.
People still sometimes use the PCL entertaining. So if there's a deficient or absent PCL, yes, you can use that PCL substituting. The advantages are probably maybe easy to balance with this absent PCL. Arguably, they say there's a more range of motion, whether it is true or not. There's a lot of debate on it. Easy, easy surgical experience.
The disadvantage? You need to be very careful. You need to be very careful and balance in either case, whether it's a little TLC or yes, in both cases, but in the field substituting. If your knee is loose and flexion, there can be a Cam jump. I can give you a little more explanation here. If this if the flexion is loose here, it will be.
Femur will jump over the post and it'll happen like that. And that would be your rays. So that's a ganjam that's one of the complications in the PCL substituting the other complication, which is quite common, is the perennial trunk syndrome. Basically, what happens when you're replacing the patella? The soft tissue is formed on the superior wall of the patella under the gold standard. And that scar tissue becomes like quite big thick nodule and clunk over the edge of the box of the knowledge of the femoral component.
It can be painful, or it can be very nuisance for the patient. Every time a patient moves about 45 40 degrees extension, they feel very like a slip in the knee. If there's not much symptoms, leave it, if it's really symptomatic, then you might need to go out and take exception of. So, no, actually, I will go into the details about the cuts, how we make it if you understand the formal articulation.
The most common problem in the replacement is the male checking of the patella, and the most common reason probably is the female internal rotation. But thankfully, the we know that you angle it from that line drawn from the anterior Alex point in the middle of the patella, from middle of the patella to the table. It's a mate of the guys by definition, not the speedy ball of the pedal.
Some of them are quite fussy. So the angle basically is literally very important to be maintained. It's higher in females less than males, about 30 degrees and female and male and about 18 degrees in females. So these are the different muscles acting on the patella, whilst the medial oblique, as well as the medial and the resultant vector, they're actually pulling up straight.
That's why the patella is actually kept in properly. So increase the acute angle basically is associated with the lateral subluxation of the teller. So our goal is to achieve a normal given angle. So how we can achieve that or how we can prevent abnormal attacking? On female side, we need to avoid female component internally rotation, so do not put several components internally rotated, do not media like the female component either put the female component neutral or externally rotated.
Or put the family component in the center of the digital single or slightly larger. How can we achieve that while we're operating the different landmarks which are available to us to use to actually make our cars properly? The apex isn't the same. Epicondyle and epicondyle access will go one by one. If you look at the picture on the top, that's the apex, which passes from the deep part of the truck up to the noj.
It's also called Whiteside line, your interior and bas status car should be perpendicular to this axis. Then come the epicondyle elections, which are concerns across the two medial and lateral epicondyle, which are easily palpable in primary knee replacement, your cards and interior and the posterior should be parallel to this one. The third one is the posterior epicondyle axis, which actually runs posterior part, your interior and gut should be treated externally rotated to this line, which axis we commonly use.
It's very important we commonly use the posterior axis because that's where the jigs actually the feet of the jigs rest on. And then from there we make our own adjustments. So that's why in most of the processes, we externally rotate three to five degrees. So coming back to the female criminal college, we know the medial female epicondyle is actually slightly larger, larger and extends distally as compared to the lateral side.
And the top end of the tibia makes a 3 degree virus cut here, so we cut the tibia perpendicular to the anatomical or mechanical axilo the tibia, which is the same. By doing so, we're cutting more on the lateral side that's on the medial side. But the federal side, we need to cut. Perpendicular to the mechanical axis, which was coming from the femoral head to the center of the distal femur.
By doing so, we got more on the medial and less from the lectern and resultant will be a rectangular extension gap. That's what we need to match that we need. Similar rectangular flexion gap as well. How we can do it. You need externally rotate your game 3 degrees because you are taking the posterior reference wheel. We will discuss in a minute and Australia, we're using this as a reference to see epicondyle.
We have a feed of the G8, so we sternly rotate so that will cut more on the medial less than the lateral procedure. There are few designs which actually have got a trapezoidal selection gap, which is to a few members there, but that's a different philosophy. We will have, we can discuss later on. So the idea is that we should have rectangular selection as well as extension gaps, and they should be symmetrical and equal.
It on the table side, but what we can do to prevent the ephemeral tracking. The tibial component, the center of that should lie at the junction of medial 3 and lateral 2/3 of the tibial tubercle. If you internally rotate the tibial component, when you extend the knee, the knee will externally rotate and the tibial tubercle will go laterally and it will increase the angle and will actually cause a subluxation of the patella.
So people component media one third and led to the third of the TV worker. Resurfacing patella always put patella media. It helps the right avoiding what I love about how which which can cause. But the problem with the selection.
So next, what's the fencing technique we should use anterior or posterior? Doesn't it make any difference? Whatever you do, the idea is to achieve the correct rotation of the family component and the size of the family component. I can tell you one thing is important. I mean, they have a lot of matters of doing interior referencing, policy addressing, referencing.
There's no right and wrong. I always do policy referencing my many colleagues do interior as well. But at the end of the day, you need to achieve proper sizing and the rotation of the federal government. And I wrote, as I can read, if your when you are doing the femoral sizing, if your thighs. Matches like with the AP damage, especially with the component like, say, the size 5.
Then doesn't it matter, you use a tuberosity referencing you're getting the same amount, anteriorly and posteriorly over the film, if you're the measuring measurement matches with the component available. However, if they be damaged, ulnar nerve famous family epicondyle in between the sizes between 4 and 5. Then you think different referencing will cause a different will cut the different amount of bone anteriorly and posterior?
It all depends which referencing techniques you use. So if I. If you have got. For example, 4 and 5. OK and you want to use the size you decided to use file size 5. If when you made it your file sizes between 4 and five, the posterior referencing you will cut same amount always.
In the pursuit of justice referencing it, the same amount will be called Australian. In Brazil referencing, if you're using side 5g, your profits will be very prominent here, will be lifted of the femur and you will stuff that family joint. But if you use side for industrial fencing, you still will be getting the same amount of yearly up here. But the interior it can cause energy.
You understand this is very important. Similarly, if you're using a referencing. And if you use file size five, the anteriorly, it will lie quite nicely with the female in India referencing whatever size you use, you're getting the same amount a It's a posterior which you got more or less. But if you use size 5. In India referencing, you've got whatever amount has been cut, it will nicely flush with the fame, the stadium, you will go to a little and there will be tight selection gap.
On the other hand, if you use smaller size. A the same amount of bone is gut, however, for in you will cost too much of bone like appear the deadline. And there can be a flexion gap in stability. So these two techniques, they're very, very important to understand. It doesn't matter whichever technique to use. And with the interior lieutenant, single posted, referencing the idea that you should have chosen appropriate size and accurate rotational alignment of the femoral component, that's literally the key here message.
If there's any male rotated femoral components, they'll have a poor gender checking. They can have any pain. Lots of motion loss function and implant implant can fail. So any designs, I mean, there is quite this really needs is by its own, it's really a full topic. But I can just little go through with the unconstrained and constrained unconstrained. Is that retaining and substituting constraint 1 is hinged on heat.
It can be fixed versus mobile bearing. It leads really itself. Have separate lectures. So there are different methods of doing the balancing or doing the cutting in the pool. In majority of the cases, we do mechanically aligned techniques with military dissection. Most of the people do this. However, some people use gap balancing the techniques.
So far, we have used using the AP axilo, the female trans epicondyle index of the femur and the posterior legs of the femur that actually is called manier. The dissection technique you measured with the jigs and you know where you put it and you know how much external rotation you want to actually create inside. So you actually from the jig, you do yourself. That's why it's going to make the reception technique in depth, balancing you balance the ligaments release.
Do the releases do the tibial cut first? Then you put a jig inside and put a femoral inside as well as differentiate. Then you bring the knee to 90 degree. Whatever the femoral component rotates externally, whatever the degrees, you fix it and then cut it. That's called gap balancing. We are a consultant doing hips and knees. One does get gave balancing on the sole mate.
There's no right or wrong. Both techniques are good. So in summary. What we need to achieve. We need to achieve the patient should be pain free and patient, should have the restoration of the function of the knee. Well, how can we achieve that? Basically, we need to achieve the proper anatomy and the ligament tension in the knee of.
So there were a few other actually I didn't really. I think she needs again a separate lecture computer assisted surgery, robotics, virtual reality software, pressure sensors and all these things they need to have, like separate. I just put that they should know that there are a few other things in the new placement as well. Now come the questions, and I think Justin probably have done it.
So I'm ready to go through it with you, with the ball and also the questions if you like to. Yeah, I think so, we go through the questions now, so I would appreciate if everybody can go through and the questions that now turn up in front of you. And then just answer as soon as you can, which of the following defines the mechanical acts of normally aligned limp.
The I think the most of them, the correct, the vertical line drawn from the femoral head through the center of the knee down to the center of the ankle. So majority are correct. The second one, performing a knee of the knee is stable and full extension, but it will not flex beyond 90 degrees and flexion is tied. Which of the following adjustment can achieve satisfactory range of motion and stability in flexion and extension?
I think all 82% said downsizing the femoral component, which I think is correct. The next is during the trial, the reduction in care or the surgeon was unable to fully extend the knee and the tibial tray lifts off when the knee is flexed past 90 degrees. What technique should be taken to obtain a balanced knee in flexion and extension to more proximal tibia?
I think that's correct. And the 66% right? They're in totally outclassed and excessive posterior femoral resection will lead to which of the following situation. Blues collection gap, yes, 91% The answers quickly during trialing in primarily are totally out last, the need does not extend into full, but flexion gap is nicely balanced after appropriate soft tissue releases have been performed.
What is the next most suitable step to balance the joint? He would have done. The second is female, 10, 73% people on Sunday, and I think that's correct. London, most of them has been clarified during your lecture, so there were questions about gap balancing versus measured reflection. I think you've explained it quite well in the candidates. Quite happy from that point of view as certainly, I think the next question.
Sorry, I lost it now. So so there was a question from Mr. ulnar nerve, who talks about where the trial's been inserted into the knee and the knee stabling extension, but inflection. The medial part feels a bit tight more than lateral, and the public doesn't seem to fit in the Mediasite. I guess it must be to do with his personal experience. It seems very, very specific about his question.
It's asking what to do next. I think the media side is tight to. They're probably the few things which can happen. Either the media releases are not sufficient that they need to address if they're too fast. So take them down. And maybe you cut more into bogus tibial cut. So you have to relook at that and see if your cut is correct, really.
Because if you tibial cut is like in guess, you cut more on the lateral less than the medium that can cause of this problem. So there are multiple really things that you need to look into. There's not one single thing I agree. I think I think also, if you are thinking about it being balanced with expansion, perhaps you need to be concerned that maybe your femur is in internal rotation as well, which is why on slap your media site tighter.
So certainly, I think you just have to relook at all your rotation and make sure that's correct as well. So and I think there is another question. This question for Mr. godsey, who is talking about roll back phenomenon. So he's asking about is the rolling back of normal phenomenon that you need to achieve with the implants or you need to avoid?
What is this significant? Yeah, this is all back in normal knee. When there's an ACL intact, that's a normal phenomenon. That's your physiological like something which happens in the knee. When we do knee replacement, the modern one, we sacrifice one or the bolt is, you know, the PCL in ACL when you sacrifice ACL, which we normally do see like training.
So in that case, it's not a true roll back. But yes, it does cause some sort of roll back because the hinge one hinge and the back is intact, which is BCL. It does actually force the femur to roll back. But as I said in my talk, it's not 100% true roll back. There's also some slide as well with it. So to have a pure roll back phenomena, you need a flat polyethylene, which we can't afford that will be very unstable.
We need Congress always even see our views congruent polyethylene, which basically the flat surface can cause contact point contact and can cause joint loading, which is more stress on one point and can cause a rapid failure. So it's a little compromise in both. Yes, we aim to achieve rollback, but not 100% Yeah, I think that's correct. So and so one final question is, I guess, the answer, probably, Yeah.
So does the previous look of fact gap balancing Mr. Nash is thus does the tibia slope affect cap balancing? Basically in when you get balancing, you're using basically first you release your soft tissue, do the tibial cut as you need to do three three degree or seven degrees to three slope, which I will implant. You're using the prostheses in general, you'll use three in next use.
Seven it depends really how much? If it is too much, obviously still slow, you balancing will definitely be affected. OK so you have to be really have to be like a balancing both sides. You can't really have too much slope with a view to have achieved more flexion. You need to keep with your prosthesis. You're using in a way that you can achieve the balancing in the soft tissue.
So when you've done that, you put in then femoral component. Wherever it goes, it will go out of your control. So it moves with the tibial chip. And that way you fix the components femoral and then you dissect it. I think that's I think the most important is to get the posterior still correct, isn't it? Yes, absolutely. And so I think there's a couple of more questions, but I think we've probably got to start doing the Viva session.
And I guess we will so we can try and answer it on a chat function. I don't know what you think of it for time purposes. We can answer them for the chat function. Yes no problem. Let you take over the screen and just do. We've got three volunteers. fact, we've got four volunteers today, but I think we've got time for 3 and we'll let the first one.
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