Cadmore media player playing video Clinical Basic Sciences for Postgraduate Orthopaedic Exams
Video Player
Accessibility
Using forms mode, you can utilize keyboard shortcuts to make usability more efficient.
Space bar will play and pause the video. Pressing escape will close all displays and pressing it again will jump to the end of the player.
You can press A to open the Keyboard Shortcut Dialog which also provides an audio description of the player and all of its features.
Language
1x
Play Speed
Adjust Volume
Transcript
Search
Result Count
of
Click to jump to result
Search
Re-center
Segments
Result Count
of
Click to jump to result
Search
Name:
Clinical Basic Sciences for Postgraduate Orthopaedic Exams
Description:
Clinical Basic Sciences for Postgraduate Orthopaedic Exams
Thumbnail URL:
https://cadmoremediastorage.blob.core.windows.net/650de225-0bd1-4ecb-a6de-4cc03a9fe6b5/videoscrubberimages/Scrubber_1.jpg
Duration:
T00H42M15S
Embed URL:
https://stream.cadmore.media/player/650de225-0bd1-4ecb-a6de-4cc03a9fe6b5
Content URL:
https://cadmoreoriginalmedia.blob.core.windows.net/650de225-0bd1-4ecb-a6de-4cc03a9fe6b5/Clinical Basic Sciences For Postgraduate Orthopaedic Exams.mp4?sv=2019-02-02&sr=c&sig=VAUi9fr4Xva%2BHbEwPSAPzgOq6JcG4uRzKEKzIji8e7s%3D&st=2024-11-24T00%3A13%3A21Z&se=2024-11-24T02%3A18%3A21Z&sp=r
Upload Date:
2024-05-31T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
Welcome to another Wednesday session. This is a combined session with orthopedic Research UK or UK and the first group.
We are very happy today to present Mr. Zahir Nawaz. He's a revision specialist, interest in frimley park. He's had opportunity to work and gain experience in several tertiary students, both in the UK and abroad. And as I've completed an international trauma fellowship in calgary, he's completed the European K fellowship in Italy, and he graduated from Imperial College London and completed its basic surgical training both in London and a registrar, the famous London location.
He has an excellent background in teaching, and I've taught previously in on these courses, including writing in and St Peter's parks. That's where I remember meeting you, Mr. Nawaz. I was at the writing course. You were amazing. Thank you. The he also has an avid interest in research on multiple international presentations and several publications, including the world's largest cohorts in the cartilage transplant.
Mr Nawaz is today going to give us a presentation on the clinical basic science. Those of you who know me know that I consider this the most important topic in the entire syllabus because it's the basis of our entire syllabus. So I'm really looking forward to this talk. We'll start with the talk from Mr. Nawaz. Then we have invited questions and then we'll have example questions from his registrar and egawa, who recently passed the exam and will, after a 2/8/35 will close the session there and start our Wednesday evening session, which will be the unrecorded portion of this teaching session today.
Without further ado, Mr. Really, looking forward to hearing your talk. Thank you so much. All right. Hello, everyone. Everyone said this is probably one of the most important topics in the exam. Almost certainly every single Viva station somehow relates back to basic science, so I've kind of based this lecture on few clinical cases, which we'll go through.
We'll cover some of the kind of standard kind of basic science that goes around it. So it's to be slightly lecture based, but it will be based on important things that you need to know and be able to discuss in the exam. OK, so it's not me. It's not a problem. All right, right? So we're going to talk about practicing healing and nonunion.
It's basically the Communist question you can get in the exam in some way or another. You're going to get a bit of failed math to work. A fracture nonunion is classic, so one out of two candidates will get something along these lines. So the approach to the question is talking about the fracture itself, the soft tissue envelope, the metalwork, the alignment, and a little bit about the host. But actually, it's this down here, the metal work bit and the fracture personality where they want you to bring your basic science.
And what type of implant would you use? How do you deal with the defect or the nonunion? Do you think that a fracture has failed or hasn't got on to healing? So this bit is very much a basic science question. So it's very, very common in trauma to talk about basic science, and it is important that you understand trauma. Basic science.
OK, so this is my favorite slide. Anyone who's been told by me always gets this slide. So this is your classic example of a fracture with a plate failure, and it is important that in the exam you highlight the important things. OK, so the priority here is to see that this is a very community fracture, and the most important word in the exam probably is to say segmental.
You have a fracture line here, you have a fracture line here. So this is a segmental fracture, which immediately tells the examiner you understand that this is a high energy injury. This immediately. That also implies that we're talking about the soft tissue, the blood supply. You then comment on the lateral view where you could talk about the bone looking sclerotic.
So again, one of my Cardinal rules in the exam is if you ever see metal work in the exam, you always have to say the word. Could this be infected? OK with the metal work? We don't talk about the metal work. So in this situation, they've used what is called a DCS plate. So screw device with what is a non locking plate.
And we're going to go through what we look at when we're talking about plate fixation. So what mode is this plate being used in? So most people would say that this place being used in a bridging mode, which is what most people say now, it is important to understand that when we're bridging, the idea is that we are essentially creating an internal fix, aren't we? So the idea is that the screws take the load that bypasses the plate and then it comes back down through the DCS screw.
Now this is a non locking plate. So in effect, this cannot bridge the fracture. So this is what we call a load sharing device. So this is sharing the load with the fracture. This is not a load bearing device, which is your typical bridging plate. It's a load bearing device to start with. And then as the fracture heals, it gradually becomes a load sharing device.
Now, if we imagine what this play is doing in the first 24, 48 hours of the patients standing up, you can imagine that plate is essentially taking the entire load and the screws are moving within the plate. So it is important to understand that when you're using a bridging plate, a bridging mode, we have to use locking plates. OK so this in effect is a spanning plate.
This is a weight bearing plate, and it's sharing it with a fracture. So we're going to come back to why that's important. So in the exam is string theory comes up a lot in the fracture. OK, so this imaginary curve that exists. No one knows what these values are, except we know it's based around 2% What we know is very strange. Theory looks at strain, so that is the change in length over the original length.
OK so what that means is if there's lots and lots of movement, which is this area down here of the curve, I hope you can see my arrow. Then that basically means that there is going to be so much movement of the fracture site that you are not going to get union and you're going to get fibrous tissue or granulation tissue, depending on how much movement there is at the fracture site. Whereas if we go right to the other end of the curve.
And this is probably what we see more often these days, we're much more understanding of that is that if we make it too stiff, i.e. the change of length is so minor, so little that the implant is so stiff that actually there is no ability for the fracture to unite either. But no one knows what this little figure is right down here. What we knew is we want about 2% of strain, around 2% OK, so that's what we're aiming for.
So in the exam, when we're talking about that plate where we just saw what we want to know is how much movement is happening at that fracture site. OK and then similarly, if we look at my next slide, which is going to come up, this is the same plate with a different fracture. And you can clearly see that the amount of movement that you expect with construct one construct to construct 3 and construct 4 would be completely different.
And again, think of it like an external fixator. How much movement are you going to get? OK, so you need to think about how many screws you're going to put in, what type of device you're going to use when you're talking about metal work and the fracture pattern. So a simple transverse fracture? Do you actually need to bridge it? The answer is probably not.
You just need compression. Whereas if you've got something like this where you don't want the weight going through it, then you want a bridging mode. So therefore you need to then think about how much strain or how much movement you want at your fracture. So if this is an extremely comminuted fracture compared to, say, something like this over here, then you would probably end up putting more screws in here to try and hold it in the incline to 2% range.
Because if you just did two screws far away, two screws far away, then the amount of movement, you know, the fracture would be quite significant, whereas in a fracture like this, actually two screws either side would actually be quite reasonable. So the idea being is that when you're doing these fixations, the idea is to try and work out the right amount of movement of the fracture. And that's quietly experience of understanding.
But there is lots of evidence to say we talk about the near far construct talking about screws far away and screws nearby, and we'll come back to that because that's something else that's quite important. So this is what I'm talking about when I talk about spanning play or is this play dead? OK, so this is a spanning play that's spanning a comminuted risk joint. It's not being used in bridging mode, it's just jacking out the joint and almost using ligament taxes to hold the fracture in the right place.
But if the patient tries to move this arm or wrist, then it's actually going to start moving at the screw plate interface rather than a locking plate where you get this. Again, this diagram of the force coming up, going through the screw, going across the plate, bypassing the fracture and then back through the bone. OK, so it's an important concept when you're talking about bridging. So again, the reason behind the bridging and the locking screw is that failure requires a significant failure of one side of the entire construct, rather than potentially one or two screws.
So that's why we're now going to very articulate plates are all locking plates near the they're the joint surface because they get much more hold and then at the top end, we then encourage the use not locking to essentially get the plate on. And then locking to basically provide that bridging mode. OK so the movement in a locking construct has to be with the whole plate. The whole plate has to move in unity, whereas in a non in a non locking construct, the movement occurs between the screw head and the plate.
OK, so. When we're talking about that, then we need to basically go right, we're happy using bridging plates. We understand the concept of strain. We understand that we need a bit of movement for our fracture to heal and we need that movement to be enough that we don't get a nonunion it stiff.
So here again, this diagram is designed in a similar way to talk about where do you put your screws? Do you put them close? And in this construct, you can see four screws on either side very, very close to fracture. So you can see the amount of distance there and the amount of movement you're going to achieve, is going to be almost negligible. Ok?
it's going to be tiny. Whereas when you have this scenario, the further the screws away, the more movement you're going to achieve at the fracture. And from your point of view, you're going to get more chance of union. This is where the concept of working length also comes in, because when we're talking about working, like most people talk about working length of a nail and they're very happy to talk about a working length of a nail because they say it's from the diocese to the most, the most the next screw on the other side of the fracture.
That's what's doing the work. So similarly, in a play, how much of the play is doing the work? So think of a plate as a lever. And similarly, here, if you've only got a centimeters worth a plate doing all the work, that is an extremely stiff construct. The amount of force required to bend that bit of plate when you've got so much fixation versus that is very different.
So working length helps with your strain environment. So that's again, something to be aware of, and these are the concepts that they will ask you in the exam. So again, locking plate, look at it as the next fix, so when you look at this construct, if you put 2x fixed pins relatively far away with a bar, is that a stable construct? Yes, it is. If it's close enough to the fracture that it doesn't wobble, then you've got a good, stable construct that you can put weight through and it will work.
In this scenario. You've got a standard transverse stretch and you've essentially put 4x six pins in for X pins and not the other side. And you've basically put the rod right across and there's very little movement. And again, that is just far too stiff for the fracture to ever heal. So I always think as a bridging player, as a fixed device, a bit like here.
So again, those pins are really important. So you look at this construct, sorry, I couldn't find a picture of someone putting 2x is really close, but two screws right next to the fracture, two screws right next to fracture. The movement of this site is almost negligible, whereas if you have a construct like this, you've got a much better straight environment, which is balanced with a long beam that has a working length here.
And these bits of the play are pretty rigid. So you've got a nice big construct, ok? And again, the concept of how stable is this X fixed with two pins here, one pin here. The chances are this is a very unstable construct. So if you put a plate in a similar fashion, would that be sufficient? And the answer is no, it wouldn't. OK, so we don't talk about the concept of what we call on axis and off axis fixation.
So people are used to this. The whole idea is with a DHS or a nail, you put the plate or you put the device as close or shorten the lever arm as best as you can. When there's torque involved. So with any comminuted fracture where you're going to bridge, there's essentially going to be a bending force. Therefore, there's a virus or about this force supply to the device.
Therefore, from your point of view, the plate is best at resisting that with the shortest lever on. OK, so in the concept of a proximal femur, it's very simple. If you've got a subtropics fracture and you put a d.h.s in, there is much more torque and the lever arm is much bigger because the plate is on the lateral aspect of the femur.
Whereas when you put a nail in, it's in the intermodal cavity and therefore the lever arm is much shorter. Therefore, it's designed to resist torque or rotation. So again, my concept of the seesaw? You've got your fulcrum, you've got your lever arm and your force being applied to the end of the beam. So the closer you can move that from Chrome over to where the load is being applied, the more stable and more resistant that is.
Now with a nail, it's a very simple concept to understand with the plate, it's people need to understand that we also have off axis fixation. So when we play to femur and I promise you, this isn't one of mine, but when we play fema, we're actually plating it in a mechanically disadvantaged position because we play laterally. The weight bearing axis of FEMA is actually through the medial side.
So the best place to put a plate like on this diagram over here is to put it immediately. But the reason we don't go there is obviously the adductor canal and the femoral and all the blood vessels that occur around here. But actually, by mechanically a medial plate is much more in favor than a lateral plate. So the minute we put a lateral distal femur plate, we are essentially creating a bending moment because the plate is over here off the axis.
OK, so one of the classic examples of an on axis classification is the nail, but that actually still off axis to a degree. So what we actually describe as pure on axis fixation is a loser a-frame because the wires crossed through the center of the bone. And when you load the frame, the force is applied down the weight bearing axis of a literal frame.
So any of you that are done in is are afraid will understand the concept of getting the frame to be on the mechanical alignment of the bone, not along the anatomical alignment of the bone. It's all about making sure that those wires are on the mechanical axis. And that's why a laser a frame is so good at getting fractures to heel. If you have on axis fixation, you have anatomical reduction and you get good stability and strain environment across your fracture.
You will get your fracture to heal. And those are all the concepts that your complex surgeons that do non-union surgery will use to decide how they fix a nonunion or email union. So back to this fracture, we talk about the fracture personality, so in the exam we talk about it's dominated. The fracture is over a large zone of injury, high energy fracture pattern because it's segmental. We have to query whether it might have been opened at the beginning, and we have to query where the bone is dead.
Because if you look at that lateral view, you can certainly see that there sclerotic bone there. We talk about a soft tissue envelope. You must always comment on any fracture when you see that, so it's high energy, so we're worried that there is lots of soft tissue stripping. When we get to the metal work, we comment on the metal that was used. So what mode is what the examiners are interested in?
And you can look at that by being able to recognize whether it's a locking or a non locking device or the screws used. We're talking about the bridging mode or what mode the plate's been used that the working length. And then whether it's an off axis fixation and whether the implant has reduced the fracture and restore the mechanical alignment, which is the most important thing in anything that heals and then obviously at the bottom is highest, which in the exam is obviously less important.
Even though you need to mention it, the exam is centered all over this part of the discussion. One of the things that broke metal work always generates is the vibrant fatigue failure, so fatigue failure, the definition you must learn, OK, so cyclical loading, which eventually leads to failure of the implant, which occurs. And this is the most important statement in a single subthreshold load or a physiological load.
So that basically means that the play is designed to take a significant amount of load and the plate will break at a certain load with one load that's called our ultimate tensile strain. We get a point on the plate where if you load it below that limit, it doesn't matter how many cycles you do, the plate will not break. So that's our endurance limit.
So typically we talk about this curve. Now, this curve is really important to understand, so you guys will understand it. So on this axis down here, we're talking about the number of cycles. There's a logarithmic scale. So from a testing perspective? Companies use tenotomy million as their endurance limit, so if you load this amount of newtons per meter or stress.
But this many cycles that beyond that point, the plate will never break, ok? Whereas this red line demonstrates a single cycle where the plate breaks immediately, so that's our ultimate tensile strength. So that's the one single 0.1 load with one amount of load, and it breaks instantly. All plates that we use in fractures work in zone A OK because essentially eventually, if the fracture doesn't heal, the metal work will fail.
OK, so the idea is that we want our plate not to be working over here where this star is, but we want to be working down here. So the idea is that we get as many cycles. Before the break, so that's all race between union and the plate breaking that we achieved this by reducing the amount of load going through the plate. And we achieved that by getting proper anatomical alignment. For a reduction, getting strain environment right, and therefore the idea being that we get more cycles.
So we get more time for the fracture to heal. So the St curve is really important now. This curve suggests that at X amount of load after, say, 20,000 cycles, if we load it at that much, the plate will fail. We now we now know with fatigue failure that what actually happens when you draw this curve is that it fails at a much lower load down here around this point. So it has that fails.
After three months, the patients only had 10,000 cycles, but the play has failed well before the curve. Now, the reason for that is, number one, we're putting a lot more load through it than the plate was designed to do it. But actually what also is happening is that the plate is deforming. OK, so just before a plane breaks, you will always see that a plate starts to bend or deform.
Now that means that this curve that we're looking at is what the plate should do if there's no deformity to the plate. We're actually as the plate starts to bend. You start to get something called necking, where the plate starts to thin. So a bit like a paperclip. When you bend the paperclip continuously, what you'll see is the point of most movement.
The two sides of the metal, the metal start to narrow and thin out, and then suddenly they give. Now on that curve, what actually happens is it's a single load. And the plate has failed. So this curve that we drew originally is what the plate would do if there was no deformity to the plate. But actually, as the plate is bending and necking, the curve is moving down and down and down and down to the point where this load suddenly comes into what we call physiological mode, so the patient doesn't fall off a building for the plate to break, because that will be this curve over here.
What happens is the patient just walks and suddenly takes one step off the curb and the plate snaps, OK, so essentially the curve for that plate has moved down. So this is a curve for the plate as it comes out the packet, and this is the curve that's occurring as a plate starts to bend and neck, which is why you get a single episode of Ultimate tensile strength, where it fails. It's a hard concept to understand, but I hope everyone understands that it comes up in the exam a lot.
Right case number two. OK, we'll do this one. So I was trauma again, a very classical case. Most people are really happy with exits. Most people are unhappy with this one, which is the Charlie. Just remember that North of the border North of Birmingham, most people use time Leeds for the cemented South of Birmingham.
Most people use exits. So you need to know both when it comes to the exam and how they work. So with the Exeter, it's important to remember it's a taper slip. It moves. It's not bonded to the cement, so it actually, in effect is an ax that is going into the femur. So what stops the femur splitting or the axes are just continuing down?
The most important concept here is this stuff, the White stuff. It's the cement. The cement imparts viscoelastic properties to the femur. So as you load, you generate what we call huge stresses. So everyone's happy with who stresses. So it's an axle load that's converted into circumferential loads. So the way, in my mind that works is it's essentially a balloon.
You blow into the balloon and it creates the tension in the rubber. As you push harder or you blow in, or as this rubber stretches more and more, the resistance to blowing in the air becomes harder and harder. Exactly the same way as an exit engages, it becomes harder and harder as the whoop stresses start to go up. The other bits, the reason the exit was asked a lot is that the cement would deform over time.
We all know that the exits are subsides by a few millimeter over the first year. We we call that creep. So again, from a normal day to day perspective, what we talk about is a bookshelf. You put a very heavy encyclopedia on there, leaving for a year and you take the book off. What happens? The shelf is plastically deformed and is left with a constant bow.
Similarly, with the cement, it will deform very slightly, with continuous impaction of the stem going up and down. And eventually this is the Exeter will settle, usually somewhere between two and 4 millimeters after the first year. The other with the elastic properties stress relaxation. So again, I think of this as a rubber band. So if you pull a rubber band as hard as you can out to its limit and hold it there, the most amount of force is required to pull it out in the first place.
And then while you hold it over time, the amount of force required starts to drop off till it plateaus to a certain point. OK, so the initial stretch creates the most amount of energy. And then as you hold that over time, it relaxes. So similarly, in an exit, we talk about stress, relaxation of that loading and unloading. When we talk about the totally, completely different concept, we're talking here about a composite OAM beam theory and we're talking about a matte finish to the stem, and therefore there is complete bonding between this the metal, the cement and the bone.
So this is what we call a Composite Medium. It's a mixture of three things now with a composite being. The loading is very different, so it does not load like a Exeter. So in a composite beam, the biomechanics of how a beam works is it will always share the load through the most stiffest part of the beam. So if there's a mixture of materials, the stiffest material always take the most amount of the load.
And then as things start to change, then that shear force will be shared with other bits. So in this scenario, with a Charnley or any composite being theory, there is so much metal at the top here that actually when you load the hip, the force preferentially goes through the stem rather than through the cement mantle or rather than through the bone. Then, as we start to go further down the hip, the metal starts to thin and therefore forces, then slowly starting to be shared with the cement and the bony mantle.
So we classically see in this scenario, which is what we call our stress shielding. So stress shielding is a stiffness phenomenon at the top. Again, we have significant amount of material. So when we load the hip, it preferentially loads through the implant to the point where it comes that the stiffness starts to reduce because there's less material in comparison to there and the bone starts are shared, you can then see the bone thickening up and taking more of the load.
So this is your classic stress shielding, ok? Again, a very common exam question talking about stress shielding and then what you end up talking about is the composite OAM beam theory and stress shielding is Wolfe's law again, basic science. If you don't apply to a bone, the bone will start to be resolved, and that's exactly what you see. I won't go through that, so last thing.
I've got a few others, but we'll go through this very quickly. Charlie stand low friction arthroplasty again, a common question in the exam. You will not get asked to draw a free body diagram of the hip. It's too well known, it's too easy, and all of the candidates know it's going to come up. What they'll ask you is. Here's a chance to talk me through it and tell me why. It's only how it works and what we're trying these principles.
So we're talking about a low friction arthroplasty. I'll say that's what Charlie called it. And there are specific things that Charlie did to try and reduce what we call the friction to the hip. Now, for me, the friction part is a slight misnomer. OK, so ignore all these funny symbols and everyone gets really panicky about this. But what we're looking at is what actually is friction and friction is a constant.
OK it's a coefficient, which is basically developed as soon as you know what the two surfaces are. Your friction is set at that point. And then other things that can affect it are the lubrication within that joint and the sliding speed and the radius. And the load applied. But at no point does it talk about anything else about offset and leg length and those sort of things.
So actually, what Charlie was talking about was not actually friction, but what he was trying to do is to reduce the amount of joint reaction force across the hip. And by doing that, what he was actually talking about is a low where arthroplasty. That's what he's trying to create. OK, now Charlie always knew that his hip stems would do brilliantly, but the weakness in his construct was always the.
And he knew that if this started to wear out, then he'd get aseptic listening and all his stems would fall out and he didn't want that. So he needed a way to minimize the amount of aseptic listening. So he needed to reduce his joint reaction force. So he realized the cup. So on a classic Charlie. I'm sorry, I'm going to go back.
You see a Mexican hat, see over me, realize this to a point. He almost breaches the media war on purpose, so he knows that media lies the cup as much as possible. He does a truck attack osteotomy, which distills a laterals to the counter, and he then uses a small head. Now all of those have a reason. So again, I've drawn it here. There's your classic free body diagram, but in effect, what I'm going to do is draw it as a seesaw.
So you go to your center of rotation. You get your force of your doctors. You've got your joint reaction force and you've got your body away and he got your lever arms. So Charlie's concept was the medial the cup. So the center of rotation goes medial. So therefore you're lengthening the lever arm for the force of the doctors. And in addition, he laterals the distillers at the counter so you increase that lever arm of the force of the adductors even further.
By doing that, the amount that the muscle needs to do to generate the same amount of force goes down. So if that's centimeters versus 10 centimeters, then you have to do far less work with the muscle to generate the same amount of work and force of a doctors in effect is proportional to your joint reaction force. OK, so by reducing your force of your doctors, you have in effect reduced your joint reaction force and thereby hopefully reduce the amount of wear that's going through your pulley.
In addition, he talked about the 22 millimeter head, and the reason he did that again was to preferentially go for linear wear versus volumetric wear. So the bigger the head, the more where you get over a larger surface area. Well, actually on a physical macroscopic perspective, you don't see a lot of wear. But what you do generate is more volume of debris, whereas with a linear wear, which is a smaller head.
So what you're generating is wear, which is much more macroscopic. You'll see the head wearing into a poly, but it's only in a smaller area. So they're actually you're generating much less poly debris and therefore you're actually getting a lot less aseptic loosening. And I'm going to stop there because I'm going to run out of time.
Otherwise there are lots of other bits. Any question? Um, Joe is being thank you very much. That's an excellent talk. There are a few questions. Joe, if you want to. Yeah, there are a few questions. Thank you very much.
First for the brilliant joke. I clarified a lot of things in my mind. First of all, what is the concept of strain distribution in comminuted fracture? OK, so essentially it's a figure in a trauma surgeons head, OK, the trauma surgeon, no one can tell you how much strain you need to put across a fracture. That's experience. OK, so but basically what you're trying to get is an understanding of how much movement there's going to be across your fracture and the combination of how many screws you put in, how long the plate is, how much of the plate you're going to make do.
The work is all depending on every single individual fracture, and that changes from fracture to fracture to fracture. What most surgeons will say is you need a balance fixation. So that's number one. So that means you don't put an ex fix on with five pins at one end and one pin at the bottom end. OK, and then when you lift, that expects it's going to be unbalanced.
So similarly, with a bridging plate you want. Eight unit cortical screws distally, so that's your classic sort of femoral plate, you don't go by cortical distally, so you have six to eight distal screws before you fracture and then at the top end, if you've got eight unit cortical screws, you want 4 by cortical screws on the other side of the fracture. OK, so you've got eight cortices either side.
That's a balanced fixation. Now the question then, is how much strain do you want across your fracture? So if it's very comminuted, you're going to go for a near fall construct with those screws because you have much more movement of the fracture. Therefore, you don't want as much plate moving because if the fracture is very mobile, then you don't want a long plate taking all that load because it's going to move a lot.
So i.e. the stiffer the construct, i.e. the tie to the fracture. Less common is the fracture, the further the screws go away. Whereas if you're very comminuted, you then bring the screws further in because you want less movement at the plate. So therefore you're controlling the amount of movement and the strain. That kind of makes sense.
Yeah, definitely make a lot of sense. Thank you very much. And the second question was in interim, nail has short lever arm, so it will be more stable. Construct right for rotation? Yes for rotation. Yeah, I think the muhamed meant the torque for the lever arm. Yeah what is the working length in plate fixation with leg screw?
There isn't one, as there isn't one. So compression, if you're genuinely using a large screw, then a bit like a fibula, your lag screws doing all the work. So in effect, your plate is a neutralization plate if you're genuinely lagging that fracture. OK the screwy thing most of the work? OK so if you've got a really big large surface area across the femur, then you're even with a single lag screw that's going to have some movement.
But what you're trying to do is essentially neutralize the rotation around your leg. So if you're genuinely lagging a fracture properly, like on a fibula? Perfect anatomical reduction lagged it into place. And then you put a plate across it that plays neutralization. OK, if you're using a lag in a comminuted fracture to bring bits together, then you're mixing concepts, you're mixing.
You're trying to get primary bone healing, but then you're using a play in bridging mode. So you're actually not doing it properly. You're mixing methodologies. So if you're going to put a lag screw across, what you're saying is I can get perfect anatomical reduction and the lag screw is doing all the work. And all I want is a plate to neutralize that fracture. The minute.
You're saying my plates actually doing some work, you're mixing concepts, OK, and then in that situation, you should be really using a bridging mode. I said, so what, what is the difference between? Is there any difference between the working length in the locking and unlocking plates? Yeah so the working life of. So that's one of the questions is the work and length of a locking plate is from the screw and the screw.
It's that the better the plate over the fracture in a non locking plate, the working length of the plate is the entirety of the plate. Because all the plate is moving. OK, because there is no stiffness and therefore all the screws are moving within the screw holes. OK, so if you loaded a non locking plate, every screw head would be taking some pressure. Whereas in a locking concept, the two screws that do all the work is the one closest to the fracture and the one closest to the fracture and the plate in between.
That's the working bit. That's the energy part of the plate. OK whereas that's the fix. Yes, it goes through the bone. The screw across the plate, back down the screw and across. So the working length of your plate is that bit. That's the bit, the plate working. And those two screws are doing all the work. You're just providing extra stabilization there and there to share to protect the plate.
OK but actually in a lock in a non locking plate when you load a comedy to fracture a bit like that first case that I showed, if you load that plate and wait there, which bit of the plate is doing all the work, it's all of it, the whole place having to work, whether it's the screw, whether it's the 17 screws at the top. All of them are taking some degree of load and the plate is trying to rip out.
So I'll gather. All right. Thank you. So well, this is a clarification question, does it mean that the plate bending the straight at the fracture site? Yes, changes. And this can be reduced by stiffer plates. Yes, correct.
So so we didn't want to change the stiffness of the plate because we wanted titanium plates because they're Young's modulus is much closer to the bone, so it's easier to judge the amount of bend in a plate. So rather that two people looked at making the plates really stiff. And all that happened is that we got more nonunion because the plates are stiff. You have to put screws so far away to generate strain that it didn't work.
So then surgeons came up with the idea of something called as well as screws, which you may have seen, which are wobbly locking screws. So you've got screws, locking screws that you put in and you fill as many holes as you want and they sit-in a little washer. And it allows them to rock whilst being locked into the plate. So that was a concept that Cynthia's tried to make to generate the fact that you could get anyone to fix a plate, but as many locking screws as you wanted.
But the locking screws were wobbly. It's a very odd concept, but if you look, you can see it's locked into the plate. But actually the screw itself was in a little washer so you could wobble. So it generated movement. So we went the other way and said, you can make it as stiff as you want from the plate perspective, but we'll try and make the screws a bit wobbly and that generates the strain.
Actually, what we found is the easiest way at this point is to get something as close to bone. And then you play with the screw concepts just to get your straight environment right. OK, thank you. Thank you very much. Yeah that's all the questions, I believe axilo.
Segment:0 .
Welcome to another Wednesday session. This is a combined session with orthopedic Research UK or UK and the first group.
We are very happy today to present Mr. Zahir Nawaz. He's a revision specialist, interest in frimley park. He's had opportunity to work and gain experience in several tertiary students, both in the UK and abroad. And as I've completed an international trauma fellowship in calgary, he's completed the European K fellowship in Italy, and he graduated from Imperial College London and completed its basic surgical training both in London and a registrar, the famous London location.
He has an excellent background in teaching, and I've taught previously in on these courses, including writing in and St Peter's parks. That's where I remember meeting you, Mr. Nawaz. I was at the writing course. You were amazing. Thank you. The he also has an avid interest in research on multiple international presentations and several publications, including the world's largest cohorts in the cartilage transplant.
Mr Nawaz is today going to give us a presentation on the clinical basic science. Those of you who know me know that I consider this the most important topic in the entire syllabus because it's the basis of our entire syllabus. So I'm really looking forward to this talk. We'll start with the talk from Mr. Nawaz. Then we have invited questions and then we'll have example questions from his registrar and egawa, who recently passed the exam and will, after a 2/8/35 will close the session there and start our Wednesday evening session, which will be the unrecorded portion of this teaching session today.
Without further ado, Mr. Really, looking forward to hearing your talk. Thank you so much. All right. Hello, everyone. Everyone said this is probably one of the most important topics in the exam. Almost certainly every single Viva station somehow relates back to basic science, so I've kind of based this lecture on few clinical cases, which we'll go through.
We'll cover some of the kind of standard kind of basic science that goes around it. So it's to be slightly lecture based, but it will be based on important things that you need to know and be able to discuss in the exam. OK, so it's not me. It's not a problem. All right, right? So we're going to talk about practicing healing and nonunion.
It's basically the Communist question you can get in the exam in some way or another. You're going to get a bit of failed math to work. A fracture nonunion is classic, so one out of two candidates will get something along these lines. So the approach to the question is talking about the fracture itself, the soft tissue envelope, the metalwork, the alignment, and a little bit about the host. But actually, it's this down here, the metal work bit and the fracture personality where they want you to bring your basic science.
And what type of implant would you use? How do you deal with the defect or the nonunion? Do you think that a fracture has failed or hasn't got on to healing? So this bit is very much a basic science question. So it's very, very common in trauma to talk about basic science, and it is important that you understand trauma. Basic science.
OK, so this is my favorite slide. Anyone who's been told by me always gets this slide. So this is your classic example of a fracture with a plate failure, and it is important that in the exam you highlight the important things. OK, so the priority here is to see that this is a very community fracture, and the most important word in the exam probably is to say segmental.
You have a fracture line here, you have a fracture line here. So this is a segmental fracture, which immediately tells the examiner you understand that this is a high energy injury. This immediately. That also implies that we're talking about the soft tissue, the blood supply. You then comment on the lateral view where you could talk about the bone looking sclerotic.
So again, one of my Cardinal rules in the exam is if you ever see metal work in the exam, you always have to say the word. Could this be infected? OK with the metal work? We don't talk about the metal work. So in this situation, they've used what is called a DCS plate. So screw device with what is a non locking plate.
And we're going to go through what we look at when we're talking about plate fixation. So what mode is this plate being used in? So most people would say that this place being used in a bridging mode, which is what most people say now, it is important to understand that when we're bridging, the idea is that we are essentially creating an internal fix, aren't we? So the idea is that the screws take the load that bypasses the plate and then it comes back down through the DCS screw.
Now this is a non locking plate. So in effect, this cannot bridge the fracture. So this is what we call a load sharing device. So this is sharing the load with the fracture. This is not a load bearing device, which is your typical bridging plate. It's a load bearing device to start with. And then as the fracture heals, it gradually becomes a load sharing device.
Now, if we imagine what this play is doing in the first 24, 48 hours of the patients standing up, you can imagine that plate is essentially taking the entire load and the screws are moving within the plate. So it is important to understand that when you're using a bridging plate, a bridging mode, we have to use locking plates. OK so this in effect is a spanning plate.
This is a weight bearing plate, and it's sharing it with a fracture. So we're going to come back to why that's important. So in the exam is string theory comes up a lot in the fracture. OK, so this imaginary curve that exists. No one knows what these values are, except we know it's based around 2% What we know is very strange. Theory looks at strain, so that is the change in length over the original length.
OK so what that means is if there's lots and lots of movement, which is this area down here of the curve, I hope you can see my arrow. Then that basically means that there is going to be so much movement of the fracture site that you are not going to get union and you're going to get fibrous tissue or granulation tissue, depending on how much movement there is at the fracture site. Whereas if we go right to the other end of the curve.
And this is probably what we see more often these days, we're much more understanding of that is that if we make it too stiff, i.e. the change of length is so minor, so little that the implant is so stiff that actually there is no ability for the fracture to unite either. But no one knows what this little figure is right down here. What we knew is we want about 2% of strain, around 2% OK, so that's what we're aiming for.
So in the exam, when we're talking about that plate where we just saw what we want to know is how much movement is happening at that fracture site. OK and then similarly, if we look at my next slide, which is going to come up, this is the same plate with a different fracture. And you can clearly see that the amount of movement that you expect with construct one construct to construct 3 and construct 4 would be completely different.
And again, think of it like an external fixator. How much movement are you going to get? OK, so you need to think about how many screws you're going to put in, what type of device you're going to use when you're talking about metal work and the fracture pattern. So a simple transverse fracture? Do you actually need to bridge it? The answer is probably not.
You just need compression. Whereas if you've got something like this where you don't want the weight going through it, then you want a bridging mode. So therefore you need to then think about how much strain or how much movement you want at your fracture. So if this is an extremely comminuted fracture compared to, say, something like this over here, then you would probably end up putting more screws in here to try and hold it in the incline to 2% range.
Because if you just did two screws far away, two screws far away, then the amount of movement, you know, the fracture would be quite significant, whereas in a fracture like this, actually two screws either side would actually be quite reasonable. So the idea being is that when you're doing these fixations, the idea is to try and work out the right amount of movement of the fracture. And that's quietly experience of understanding.
But there is lots of evidence to say we talk about the near far construct talking about screws far away and screws nearby, and we'll come back to that because that's something else that's quite important. So this is what I'm talking about when I talk about spanning play or is this play dead? OK, so this is a spanning play that's spanning a comminuted risk joint. It's not being used in bridging mode, it's just jacking out the joint and almost using ligament taxes to hold the fracture in the right place.
But if the patient tries to move this arm or wrist, then it's actually going to start moving at the screw plate interface rather than a locking plate where you get this. Again, this diagram of the force coming up, going through the screw, going across the plate, bypassing the fracture and then back through the bone. OK, so it's an important concept when you're talking about bridging. So again, the reason behind the bridging and the locking screw is that failure requires a significant failure of one side of the entire construct, rather than potentially one or two screws.
So that's why we're now going to very articulate plates are all locking plates near the they're the joint surface because they get much more hold and then at the top end, we then encourage the use not locking to essentially get the plate on. And then locking to basically provide that bridging mode. OK so the movement in a locking construct has to be with the whole plate. The whole plate has to move in unity, whereas in a non in a non locking construct, the movement occurs between the screw head and the plate.
OK, so. When we're talking about that, then we need to basically go right, we're happy using bridging plates. We understand the concept of strain. We understand that we need a bit of movement for our fracture to heal and we need that movement to be enough that we don't get a nonunion it stiff.
So here again, this diagram is designed in a similar way to talk about where do you put your screws? Do you put them close? And in this construct, you can see four screws on either side very, very close to fracture. So you can see the amount of distance there and the amount of movement you're going to achieve, is going to be almost negligible. Ok?
it's going to be tiny. Whereas when you have this scenario, the further the screws away, the more movement you're going to achieve at the fracture. And from your point of view, you're going to get more chance of union. This is where the concept of working length also comes in, because when we're talking about working, like most people talk about working length of a nail and they're very happy to talk about a working length of a nail because they say it's from the diocese to the most, the most the next screw on the other side of the fracture.
That's what's doing the work. So similarly, in a play, how much of the play is doing the work? So think of a plate as a lever. And similarly, here, if you've only got a centimeters worth a plate doing all the work, that is an extremely stiff construct. The amount of force required to bend that bit of plate when you've got so much fixation versus that is very different.
So working length helps with your strain environment. So that's again, something to be aware of, and these are the concepts that they will ask you in the exam. So again, locking plate, look at it as the next fix, so when you look at this construct, if you put 2x fixed pins relatively far away with a bar, is that a stable construct? Yes, it is. If it's close enough to the fracture that it doesn't wobble, then you've got a good, stable construct that you can put weight through and it will work.
In this scenario. You've got a standard transverse stretch and you've essentially put 4x six pins in for X pins and not the other side. And you've basically put the rod right across and there's very little movement. And again, that is just far too stiff for the fracture to ever heal. So I always think as a bridging player, as a fixed device, a bit like here.
So again, those pins are really important. So you look at this construct, sorry, I couldn't find a picture of someone putting 2x is really close, but two screws right next to the fracture, two screws right next to fracture. The movement of this site is almost negligible, whereas if you have a construct like this, you've got a much better straight environment, which is balanced with a long beam that has a working length here.
And these bits of the play are pretty rigid. So you've got a nice big construct, ok? And again, the concept of how stable is this X fixed with two pins here, one pin here. The chances are this is a very unstable construct. So if you put a plate in a similar fashion, would that be sufficient? And the answer is no, it wouldn't. OK, so we don't talk about the concept of what we call on axis and off axis fixation.
So people are used to this. The whole idea is with a DHS or a nail, you put the plate or you put the device as close or shorten the lever arm as best as you can. When there's torque involved. So with any comminuted fracture where you're going to bridge, there's essentially going to be a bending force. Therefore, there's a virus or about this force supply to the device.
Therefore, from your point of view, the plate is best at resisting that with the shortest lever on. OK, so in the concept of a proximal femur, it's very simple. If you've got a subtropics fracture and you put a d.h.s in, there is much more torque and the lever arm is much bigger because the plate is on the lateral aspect of the femur.
Whereas when you put a nail in, it's in the intermodal cavity and therefore the lever arm is much shorter. Therefore, it's designed to resist torque or rotation. So again, my concept of the seesaw? You've got your fulcrum, you've got your lever arm and your force being applied to the end of the beam. So the closer you can move that from Chrome over to where the load is being applied, the more stable and more resistant that is.
Now with a nail, it's a very simple concept to understand with the plate, it's people need to understand that we also have off axis fixation. So when we play to femur and I promise you, this isn't one of mine, but when we play fema, we're actually plating it in a mechanically disadvantaged position because we play laterally. The weight bearing axis of FEMA is actually through the medial side.
So the best place to put a plate like on this diagram over here is to put it immediately. But the reason we don't go there is obviously the adductor canal and the femoral and all the blood vessels that occur around here. But actually, by mechanically a medial plate is much more in favor than a lateral plate. So the minute we put a lateral distal femur plate, we are essentially creating a bending moment because the plate is over here off the axis.
OK, so one of the classic examples of an on axis classification is the nail, but that actually still off axis to a degree. So what we actually describe as pure on axis fixation is a loser a-frame because the wires crossed through the center of the bone. And when you load the frame, the force is applied down the weight bearing axis of a literal frame.
So any of you that are done in is are afraid will understand the concept of getting the frame to be on the mechanical alignment of the bone, not along the anatomical alignment of the bone. It's all about making sure that those wires are on the mechanical axis. And that's why a laser a frame is so good at getting fractures to heel. If you have on axis fixation, you have anatomical reduction and you get good stability and strain environment across your fracture.
You will get your fracture to heal. And those are all the concepts that your complex surgeons that do non-union surgery will use to decide how they fix a nonunion or email union. So back to this fracture, we talk about the fracture personality, so in the exam we talk about it's dominated. The fracture is over a large zone of injury, high energy fracture pattern because it's segmental. We have to query whether it might have been opened at the beginning, and we have to query where the bone is dead.
Because if you look at that lateral view, you can certainly see that there sclerotic bone there. We talk about a soft tissue envelope. You must always comment on any fracture when you see that, so it's high energy, so we're worried that there is lots of soft tissue stripping. When we get to the metal work, we comment on the metal that was used. So what mode is what the examiners are interested in?
And you can look at that by being able to recognize whether it's a locking or a non locking device or the screws used. We're talking about the bridging mode or what mode the plate's been used that the working length. And then whether it's an off axis fixation and whether the implant has reduced the fracture and restore the mechanical alignment, which is the most important thing in anything that heals and then obviously at the bottom is highest, which in the exam is obviously less important.
Even though you need to mention it, the exam is centered all over this part of the discussion. One of the things that broke metal work always generates is the vibrant fatigue failure, so fatigue failure, the definition you must learn, OK, so cyclical loading, which eventually leads to failure of the implant, which occurs. And this is the most important statement in a single subthreshold load or a physiological load.
So that basically means that the play is designed to take a significant amount of load and the plate will break at a certain load with one load that's called our ultimate tensile strain. We get a point on the plate where if you load it below that limit, it doesn't matter how many cycles you do, the plate will not break. So that's our endurance limit.
So typically we talk about this curve. Now, this curve is really important to understand, so you guys will understand it. So on this axis down here, we're talking about the number of cycles. There's a logarithmic scale. So from a testing perspective? Companies use tenotomy million as their endurance limit, so if you load this amount of newtons per meter or stress.
But this many cycles that beyond that point, the plate will never break, ok? Whereas this red line demonstrates a single cycle where the plate breaks immediately, so that's our ultimate tensile strength. So that's the one single 0.1 load with one amount of load, and it breaks instantly. All plates that we use in fractures work in zone A OK because essentially eventually, if the fracture doesn't heal, the metal work will fail.
OK, so the idea is that we want our plate not to be working over here where this star is, but we want to be working down here. So the idea is that we get as many cycles. Before the break, so that's all race between union and the plate breaking that we achieved this by reducing the amount of load going through the plate. And we achieved that by getting proper anatomical alignment. For a reduction, getting strain environment right, and therefore the idea being that we get more cycles.
So we get more time for the fracture to heal. So the St curve is really important now. This curve suggests that at X amount of load after, say, 20,000 cycles, if we load it at that much, the plate will fail. We now we now know with fatigue failure that what actually happens when you draw this curve is that it fails at a much lower load down here around this point. So it has that fails.
After three months, the patients only had 10,000 cycles, but the play has failed well before the curve. Now, the reason for that is, number one, we're putting a lot more load through it than the plate was designed to do it. But actually what also is happening is that the plate is deforming. OK, so just before a plane breaks, you will always see that a plate starts to bend or deform.
Now that means that this curve that we're looking at is what the plate should do if there's no deformity to the plate. We're actually as the plate starts to bend. You start to get something called necking, where the plate starts to thin. So a bit like a paperclip. When you bend the paperclip continuously, what you'll see is the point of most movement.
The two sides of the metal, the metal start to narrow and thin out, and then suddenly they give. Now on that curve, what actually happens is it's a single load. And the plate has failed. So this curve that we drew originally is what the plate would do if there was no deformity to the plate. But actually, as the plate is bending and necking, the curve is moving down and down and down and down to the point where this load suddenly comes into what we call physiological mode, so the patient doesn't fall off a building for the plate to break, because that will be this curve over here.
What happens is the patient just walks and suddenly takes one step off the curb and the plate snaps, OK, so essentially the curve for that plate has moved down. So this is a curve for the plate as it comes out the packet, and this is the curve that's occurring as a plate starts to bend and neck, which is why you get a single episode of Ultimate tensile strength, where it fails. It's a hard concept to understand, but I hope everyone understands that it comes up in the exam a lot.
Right case number two. OK, we'll do this one. So I was trauma again, a very classical case. Most people are really happy with exits. Most people are unhappy with this one, which is the Charlie. Just remember that North of the border North of Birmingham, most people use time Leeds for the cemented South of Birmingham.
Most people use exits. So you need to know both when it comes to the exam and how they work. So with the Exeter, it's important to remember it's a taper slip. It moves. It's not bonded to the cement, so it actually, in effect is an ax that is going into the femur. So what stops the femur splitting or the axes are just continuing down?
The most important concept here is this stuff, the White stuff. It's the cement. The cement imparts viscoelastic properties to the femur. So as you load, you generate what we call huge stresses. So everyone's happy with who stresses. So it's an axle load that's converted into circumferential loads. So the way, in my mind that works is it's essentially a balloon.
You blow into the balloon and it creates the tension in the rubber. As you push harder or you blow in, or as this rubber stretches more and more, the resistance to blowing in the air becomes harder and harder. Exactly the same way as an exit engages, it becomes harder and harder as the whoop stresses start to go up. The other bits, the reason the exit was asked a lot is that the cement would deform over time.
We all know that the exits are subsides by a few millimeter over the first year. We we call that creep. So again, from a normal day to day perspective, what we talk about is a bookshelf. You put a very heavy encyclopedia on there, leaving for a year and you take the book off. What happens? The shelf is plastically deformed and is left with a constant bow.
Similarly, with the cement, it will deform very slightly, with continuous impaction of the stem going up and down. And eventually this is the Exeter will settle, usually somewhere between two and 4 millimeters after the first year. The other with the elastic properties stress relaxation. So again, I think of this as a rubber band. So if you pull a rubber band as hard as you can out to its limit and hold it there, the most amount of force is required to pull it out in the first place.
And then while you hold it over time, the amount of force required starts to drop off till it plateaus to a certain point. OK, so the initial stretch creates the most amount of energy. And then as you hold that over time, it relaxes. So similarly, in an exit, we talk about stress, relaxation of that loading and unloading. When we talk about the totally, completely different concept, we're talking here about a composite OAM beam theory and we're talking about a matte finish to the stem, and therefore there is complete bonding between this the metal, the cement and the bone.
So this is what we call a Composite Medium. It's a mixture of three things now with a composite being. The loading is very different, so it does not load like a Exeter. So in a composite beam, the biomechanics of how a beam works is it will always share the load through the most stiffest part of the beam. So if there's a mixture of materials, the stiffest material always take the most amount of the load.
And then as things start to change, then that shear force will be shared with other bits. So in this scenario, with a Charnley or any composite being theory, there is so much metal at the top here that actually when you load the hip, the force preferentially goes through the stem rather than through the cement mantle or rather than through the bone. Then, as we start to go further down the hip, the metal starts to thin and therefore forces, then slowly starting to be shared with the cement and the bony mantle.
So we classically see in this scenario, which is what we call our stress shielding. So stress shielding is a stiffness phenomenon at the top. Again, we have significant amount of material. So when we load the hip, it preferentially loads through the implant to the point where it comes that the stiffness starts to reduce because there's less material in comparison to there and the bone starts are shared, you can then see the bone thickening up and taking more of the load.
So this is your classic stress shielding, ok? Again, a very common exam question talking about stress shielding and then what you end up talking about is the composite OAM beam theory and stress shielding is Wolfe's law again, basic science. If you don't apply to a bone, the bone will start to be resolved, and that's exactly what you see. I won't go through that, so last thing.
I've got a few others, but we'll go through this very quickly. Charlie stand low friction arthroplasty again, a common question in the exam. You will not get asked to draw a free body diagram of the hip. It's too well known, it's too easy, and all of the candidates know it's going to come up. What they'll ask you is. Here's a chance to talk me through it and tell me why. It's only how it works and what we're trying these principles.
So we're talking about a low friction arthroplasty. I'll say that's what Charlie called it. And there are specific things that Charlie did to try and reduce what we call the friction to the hip. Now, for me, the friction part is a slight misnomer. OK, so ignore all these funny symbols and everyone gets really panicky about this. But what we're looking at is what actually is friction and friction is a constant.
OK it's a coefficient, which is basically developed as soon as you know what the two surfaces are. Your friction is set at that point. And then other things that can affect it are the lubrication within that joint and the sliding speed and the radius. And the load applied. But at no point does it talk about anything else about offset and leg length and those sort of things.
So actually, what Charlie was talking about was not actually friction, but what he was trying to do is to reduce the amount of joint reaction force across the hip. And by doing that, what he was actually talking about is a low where arthroplasty. That's what he's trying to create. OK, now Charlie always knew that his hip stems would do brilliantly, but the weakness in his construct was always the.
And he knew that if this started to wear out, then he'd get aseptic listening and all his stems would fall out and he didn't want that. So he needed a way to minimize the amount of aseptic listening. So he needed to reduce his joint reaction force. So he realized the cup. So on a classic Charlie. I'm sorry, I'm going to go back.
You see a Mexican hat, see over me, realize this to a point. He almost breaches the media war on purpose, so he knows that media lies the cup as much as possible. He does a truck attack osteotomy, which distills a laterals to the counter, and he then uses a small head. Now all of those have a reason. So again, I've drawn it here. There's your classic free body diagram, but in effect, what I'm going to do is draw it as a seesaw.
So you go to your center of rotation. You get your force of your doctors. You've got your joint reaction force and you've got your body away and he got your lever arms. So Charlie's concept was the medial the cup. So the center of rotation goes medial. So therefore you're lengthening the lever arm for the force of the doctors. And in addition, he laterals the distillers at the counter so you increase that lever arm of the force of the adductors even further.
By doing that, the amount that the muscle needs to do to generate the same amount of force goes down. So if that's centimeters versus 10 centimeters, then you have to do far less work with the muscle to generate the same amount of work and force of a doctors in effect is proportional to your joint reaction force. OK, so by reducing your force of your doctors, you have in effect reduced your joint reaction force and thereby hopefully reduce the amount of wear that's going through your pulley.
In addition, he talked about the 22 millimeter head, and the reason he did that again was to preferentially go for linear wear versus volumetric wear. So the bigger the head, the more where you get over a larger surface area. Well, actually on a physical macroscopic perspective, you don't see a lot of wear. But what you do generate is more volume of debris, whereas with a linear wear, which is a smaller head.
So what you're generating is wear, which is much more macroscopic. You'll see the head wearing into a poly, but it's only in a smaller area. So they're actually you're generating much less poly debris and therefore you're actually getting a lot less aseptic loosening. And I'm going to stop there because I'm going to run out of time.
Otherwise there are lots of other bits. Any question? Um, Joe is being thank you very much. That's an excellent talk. There are a few questions. Joe, if you want to. Yeah, there are a few questions. Thank you very much.
First for the brilliant joke. I clarified a lot of things in my mind. First of all, what is the concept of strain distribution in comminuted fracture? OK, so essentially it's a figure in a trauma surgeons head, OK, the trauma surgeon, no one can tell you how much strain you need to put across a fracture. That's experience. OK, so but basically what you're trying to get is an understanding of how much movement there's going to be across your fracture and the combination of how many screws you put in, how long the plate is, how much of the plate you're going to make do.
The work is all depending on every single individual fracture, and that changes from fracture to fracture to fracture. What most surgeons will say is you need a balance fixation. So that's number one. So that means you don't put an ex fix on with five pins at one end and one pin at the bottom end. OK, and then when you lift, that expects it's going to be unbalanced.
So similarly, with a bridging plate you want. Eight unit cortical screws distally, so that's your classic sort of femoral plate, you don't go by cortical distally, so you have six to eight distal screws before you fracture and then at the top end, if you've got eight unit cortical screws, you want 4 by cortical screws on the other side of the fracture. OK, so you've got eight cortices either side.
That's a balanced fixation. Now the question then, is how much strain do you want across your fracture? So if it's very comminuted, you're going to go for a near fall construct with those screws because you have much more movement of the fracture. Therefore, you don't want as much plate moving because if the fracture is very mobile, then you don't want a long plate taking all that load because it's going to move a lot.
So i.e. the stiffer the construct, i.e. the tie to the fracture. Less common is the fracture, the further the screws go away. Whereas if you're very comminuted, you then bring the screws further in because you want less movement at the plate. So therefore you're controlling the amount of movement and the strain. That kind of makes sense.
Yeah, definitely make a lot of sense. Thank you very much. And the second question was in interim, nail has short lever arm, so it will be more stable. Construct right for rotation? Yes for rotation. Yeah, I think the muhamed meant the torque for the lever arm. Yeah what is the working length in plate fixation with leg screw?
There isn't one, as there isn't one. So compression, if you're genuinely using a large screw, then a bit like a fibula, your lag screws doing all the work. So in effect, your plate is a neutralization plate if you're genuinely lagging that fracture. OK the screwy thing most of the work? OK so if you've got a really big large surface area across the femur, then you're even with a single lag screw that's going to have some movement.
But what you're trying to do is essentially neutralize the rotation around your leg. So if you're genuinely lagging a fracture properly, like on a fibula? Perfect anatomical reduction lagged it into place. And then you put a plate across it that plays neutralization. OK, if you're using a lag in a comminuted fracture to bring bits together, then you're mixing concepts, you're mixing.
You're trying to get primary bone healing, but then you're using a play in bridging mode. So you're actually not doing it properly. You're mixing methodologies. So if you're going to put a lag screw across, what you're saying is I can get perfect anatomical reduction and the lag screw is doing all the work. And all I want is a plate to neutralize that fracture. The minute.
You're saying my plates actually doing some work, you're mixing concepts, OK, and then in that situation, you should be really using a bridging mode. I said, so what, what is the difference between? Is there any difference between the working length in the locking and unlocking plates? Yeah so the working life of. So that's one of the questions is the work and length of a locking plate is from the screw and the screw.
It's that the better the plate over the fracture in a non locking plate, the working length of the plate is the entirety of the plate. Because all the plate is moving. OK, because there is no stiffness and therefore all the screws are moving within the screw holes. OK, so if you loaded a non locking plate, every screw head would be taking some pressure. Whereas in a locking concept, the two screws that do all the work is the one closest to the fracture and the one closest to the fracture and the plate in between.
That's the working bit. That's the energy part of the plate. OK whereas that's the fix. Yes, it goes through the bone. The screw across the plate, back down the screw and across. So the working length of your plate is that bit. That's the bit, the plate working. And those two screws are doing all the work. You're just providing extra stabilization there and there to share to protect the plate.
OK but actually in a lock in a non locking plate when you load a comedy to fracture a bit like that first case that I showed, if you load that plate and wait there, which bit of the plate is doing all the work, it's all of it, the whole place having to work, whether it's the screw, whether it's the 17 screws at the top. All of them are taking some degree of load and the plate is trying to rip out.
So I'll gather. All right. Thank you. So well, this is a clarification question, does it mean that the plate bending the straight at the fracture site? Yes, changes. And this can be reduced by stiffer plates. Yes, correct.
So so we didn't want to change the stiffness of the plate because we wanted titanium plates because they're Young's modulus is much closer to the bone, so it's easier to judge the amount of bend in a plate. So rather that two people looked at making the plates really stiff. And all that happened is that we got more nonunion because the plates are stiff. You have to put screws so far away to generate strain that it didn't work.
So then surgeons came up with the idea of something called as well as screws, which you may have seen, which are wobbly locking screws. So you've got screws, locking screws that you put in and you fill as many holes as you want and they sit-in a little washer. And it allows them to rock whilst being locked into the plate. So that was a concept that Cynthia's tried to make to generate the fact that you could get anyone to fix a plate, but as many locking screws as you wanted.
But the locking screws were wobbly. It's a very odd concept, but if you look, you can see it's locked into the plate. But actually the screw itself was in a little washer so you could wobble. So it generated movement. So we went the other way and said, you can make it as stiff as you want from the plate perspective, but we'll try and make the screws a bit wobbly and that generates the strain.
Actually, what we found is the easiest way at this point is to get something as close to bone. And then you play with the screw concepts just to get your straight environment right. OK, thank you. Thank you very much. Yeah that's all the questions, I believe axilo.
Form Title Download
Transcript
Form Title Bookmark
Entire Media
Segment(s)
Custom Clip
Start At:
End At:
Form Title Share
Entire Media
Segment(s)
Custom Clip
Start At:
End At:
Form Title Accessibility and Keyboard Shortcuts
The cadmore media player is a professional video and audio player experience designed to deliver media as well as relevant transcript, segmentation, and metadata. On the screen is a traditional html video player with buttons such as play, pause, forward, captioning, language and play speed selection and more. Adjacent to the video player are generally tabs, one of which shows a scrolling transcript of the video and the other shows any segmentation of the media, sometimes referred to as chapters. At the top of the video is a menu bar containing an Explore button and Tools button. The Explore button allows you to dig deeper into the video by opening up an explore dialog which contains tabs for a visual navigation of the video using thumbnails, an about tab which contains rich metadata about the media, a segments tab which contains further information about the video, and a related tab which contains links to other media related to this media. The tools button opens a menu with options for sharing the media on social media, creating bookmarking links, creating embed codes for your website, generating citations, and more.
Keyboard Shortcuts
Keyboard shortcuts only work while you are in forms mode. By entering forms mode, you will be able to quickly access portions of the media player with single key commands.
Spacebar: Play/Pause Toggle
I: Info Menu,
O: Tools Menu
T: Transcript Tab,
S: Segments Tab
F: Forward 15,
R: Rewind 15
L: Languages,
P: Playspeed
M: Mute Toggle,
V: Volume Bar
N: Video Only Toggle,
B: Full Screen Toggle
C: Captions Toggle
Escape: Closes dialogs and menus / Exits Player
Z: Next Transcript Chapter
X: Previous Transcript Chapter
Q: Next Transcript Paragraph
W: Previous Transcript Paragraph
Entire Media
Segment(s)
Custom Clip
Start At:
End At:
Embed Size
-
You Size - Responsive
-
We Size - Responsive
-
Picture Overlay Popup
-
400 x 225
-
512 x 288
-
400 x 700
-
768 x 1024
-
1024 x 512
-
1280 x 608
Form Title Cite
No citation provided.
Info
Segments
Related
Thumbnails
Exit Clip Mode
You have requested to see a portion of the video outside of the clip.
Click OK to switch to the full video or click if you would like to stay inside the clip. You can always go back to the clip with Tools and Clip Mode