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Principles of Plates Fracture Fixation for Orthopaedic Exams
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Principles of Plates Fracture Fixation for Orthopaedic Exams
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Language: EN.
Segment:0 .
Signs of fracture management, but specifically about plates and plate design, the reason why this is a topic that if you haven't put any thought into it when you get hit by it, you will be shocked and you will not respond well. So it's very important that we kind of go through this. It's also a great topic because it does cover quite a number of chapters in basic science and also in fracture management.
And you can take this from plate to other forms of fixation and other forms of implants, and you can use the same basic science knowledge and apply it in different ways. So I really do recommend you do spend some time focusing on this area as well. So first of all, my declarations, these are my opinions and do not represent any organization. I have no final financial interests to declare.
Pictures of implants are in no way in endorsement of any of the implants taken from the internet as fair use for educational purposes. There's our first picture design, the perfect device and your that's the response I want to try and avoid. I don't want you saying things like I use X because I perfect or I know I know it well or my hospital uses or the rep tells me it's perfect.
That you see. Remember this image of me smacking my head and getting upset with you guys? OK, so the answer is always prepare a simple sentence for any question like this. Try and divide your answers into headings and then work on those headings. So the design of my implant would require consideration of many factors, including material properties, structural properties, interface fixation and modality of use.
I would usually say modality of use. First, depending on how I'm going to use it, then I would decide what material, structural and interface fixation devices I need. But I'm leaving this to the last because it's a bigger topic and it's worth kind of quizzing you guys on it down the line. So material properties you need to discuss Young's modulus elastic plastic yield points, the brittleness or ductile features of your device, and the toughness and hardness of them.
And remember, material properties are independent of shape, so my ideal material would be something which is inert, reliable, easily manufactured and sterilized. It should be a reasonable price or a price, which is acceptable considering we put so many into them and has a corrosion resistance idea should be ductile with. We need to know how ductile we want it and the toughness and hardness.
These are two different concepts, by the way, toughness and hardness will come to that in a moment. Examples are the materials we use commonly. Stainless steel L the 3 1 six. This is quite an important question. They do ask you about this quite frequently. What does the three stands for and what? 3% nickel 16% and the L stands for low carbon, which is any metal, which any stainless steel, which has less than 0.03% Now this is quite an important concept.
Why do we use this? We won six series. So why do we use the 300 series, but specifically the L series? The reason why is the low carbon is less is more resistant to corrosion in the human body because of sodium chloride in the body. So this is a plate on metal that's been that is used in the oceans and seas by engineers there, and it has the same resistant properties as it would have in the ocean because our bodies are essentially salt. So that's quite a quick trick to that question.
But once you get that one out, you're saving yourself trouble. The next question they usually ask is what is titanium all which which we use the six Allen for the aluminium, 6% vanadium, 4% know that vanadium does have some potential iron reaction problems, and that's potentially a question that can be asked, especially if you have scratch scratches on your titanium plate or titanium rod.
But the nice thing about titanium is it's self pacifying. OK, so that's quite a useful feature of it. Other advantages with titanium is that it's Young's modulus of edges closer to bone, and therefore it's more ductile and also works better in terms of giving you work. Things like that. However, in the conversation about this, the pros and cons, you can say stainless steel has many ways of modifying its modulus of elasticity, and we've come to those questions later.
The advantage of stainless steel is it's cheap, it's readily available. We know its properties and it's consistent throughout cobalt chromium alloys, the other one we use. But in fixation, it's rare that we use it. It's more for its surface hardness that we use it for. So what is modulus of elasticity? So if you take a diagram and give yourself force in displacement, your slope gives you your stiffness.
That's force of displacement. Very simple concept. Now we're going to make it a little bit more complicated and doesn't talk about stress and strain forces. Your stresses, your force over an area which is newtons over a meter squared or otherwise known as pastels, and your strain is your change in length or height compared 2 divided by its original length, and head has no units because you're dividing distance by itself.
OK, I'm just going over this very quickly because you do need to know these definitions very well and be able to spill them out very quickly because otherwise you'll get stuck. So then taking that same diagram instead, we use stress and we change. We use the bottom to strain and we've got our slope, which is Young's modulus of elasticity. The next thing to say is that the common materials in orthopedics, there's your numbers.
Do you notice that we say titanium as a closer elastic modulus of elasticity to cortical bone? But the reality is it's a huge difference between the two. So I'm not 100% convinced this is my personal opinion. I'm 100% convinced, but titanium's advantages in these situations, especially in plates as opposed to nails. And then this diagram, it's pretty much everywhere. I do recommend you memorize it because it has come up in the exams scenarios where they've put that picture in front of you and said, what is one?
What is two one, three 4 and so on? Essentially, what they want to know is, do you understand the relative Young's modulus compared to the bone? And where would you imagine bone would be and where each of the metals and other orthopedic implant material would be? OK, now we said, we talk about a few of the properties of a stress strain graph.
And what they mean. So the elastic property is the area where Young's modulus exists, where you get an equal and straight line, essentially where you get an equal between stress and strain. And that's at this point here. After that, you get plastic deformity. And for the purposes of this, I've drawn this quite severely. Just so we can show the different parts.
So the point is the point where you move from plastic to plastic, you're yielding area is the area where you're starting to lose strength. So use hardness, but then you start to develop a strain hardening environment. This this is important to know because this is in cold, cold welding steel called working with steel. This is where you can get ultimate tensile strength in your prosthesis so you can cold work this.
What this does is it creates the undulating molecules within your stainless steel to align up more. Well and to prevent the defects and to create a more compact spacing of the molecules together. And this gives you your most, strongest or hardest material possible, but anything after a certain point, the anything after ultimate tensile strength is lacking, and we do see necking in the early stages of failure of plates and/or prostheses and finally fracture.
Now I did say I'd mentioned the difference between strength and hardness of the properties of strength and hardness. So strength is everything the surface, the area underneath that graph. So the area underneath that graph is the strength of any metal. What it represents really is the energy required to create a fracture. While the hardness is a surface property of the material, so do make sure you understand the difference between those two, and it's quite important that you want to be able to throw out those definitions very quickly.
And now so so far, we've talked about the stress strain graphs and its modality in use in orthopedics and trauma. We've also talked about the different metals we use and we've shown. Something about them and why we use different ones, you can even go through the advantages and disadvantages graph in the Ramachandran book and you'll find that the. You'll be on safe ground straightaway.
So now we go into structural properties, these include bending stiffness, bending stiffness, torsional stiffness and axilo stiffness, so bending stiffness is pretty straightforward. By the way, this is all dependent on the shape of the material. OK, so bending stiffness is essentially, if you take any length of any material and you put pressure on the whatever the length is and bend against it, that's your bending stiffness.
Social stiffness is twisting that same material and axilo stiffness is weight bearing on the length of that material. But essentially, they're all dependent on your crossbar sectional shape of your property, so your design of your implant allows resistance to bending your if, for example, if you're using a rod. If you increase the radius of the rod, you have a more straighter construct using your second moment of inertia.
That formula is pi r to the power of 4 divided by 4. And that's quite a significant number to remember because you are you literally are multiplying. If you double something, you're multiplying it by a factor of 16 of a plate or any metal bar you're talking about with multiplied by the height or, in this case, D to the power of 3. Now that's an important concept to understand, because if you ever look at building sites, you'll always see that there are girders in the building sites and you wonder why would they use girders?
Well, there you are. That's the picture that explains it perfectly there. The bottom picture here, the girder itself, you're still preserving the height of your plate. But what you're doing is using less metal. Therefore, you have a lighter construct, and it's an important concept to remember because you're maintaining the width of your construct, you're maintaining the height of your construct, but using far less metal in that process, the same principle as your Hollow nails.
Again, less for the same amount of material. You can achieve a more rigid construct by bringing out using that material as a hollow tube. You can appreciate that there's far more material in this than there is in this. And for a small decrease in the proportion of resistance sort of decrease in the proportion of your movement area. OK now, now we're going to move on to the next part of this.
Remember, we talked about using your girders as a principal and remember that their height is preserved. That's the same principle behind the low contact plate in your low contact plate. You can now take away metal. Therefore, you need less metal. But more importantly, you now have less surface area to pressure the bone. As you can see, the height is still preserved and the witness to preserve.
But the plate is missing these small areas here, which represent this area here. OK and then that same principle we talked about with the girders is still present with your one third tubular once a tubular is usually 1 millimeter thick plate. But by putting it as a one third of a tube, you're still preserving the height, as you can see on this schematic representation there.
OK now we move on to our interface fixation, so we have a choice between conventional and locking screws and the other way to describe them as is by compression and using plate friction versus a fixed angle device. OK or you can use them in combination. And the conventional plate, you're dependent on your friction interface between the plate and the bone, so what you're doing is you're compressing your plate onto the bone.
And once you've done that, your pre-loading, you're loading the bone and then the patient own load adds up together to create. Sorry, apologize. Go back. The friction force is with the is far more than the patients load, therefore your plate constructor is going to be preserved. In terms of locking platelets, graphics, you are locking your plate, your screw into the plate, that's what those crosses represent.
That's the screw locked into the plate that's creating a fixed angle device. You're loading your patient load and you're overcoming the compressive strength of the bone. OK, so essentially you're locking device is allow is transferring the weight of the bone onto the plate. So in the stress situation, you're doing your patient loading with the different types, and you have one option of preloading this and that creates your interface, so there is a difference between your standard versus locking.
Loading and. To be honest with. And then this is demonstrating that the pull out strength is each the pull out strength of this construct is dependent on a single screw each time, and each one will individually fail. One is sequentially. While what we see with the locking plates is that you get you need you have a large resistant area, but your force requires you to make sure all your fixation fixed angle fixations to fail at one go.
So there are advantages to your locking plate. However, it's not necessarily always the right answer for this, and we'll come to why that is the case. So some of the other things we need to consider about in our plate design is preservation of blood supply, and that can be a discussion about curiosity, your blood supply and the centrifugal versus centripetal of blood flow.
You may be need to talk about when those two change over both in terms of childhood and/or childhood to adulthood, and vice versa in terms of postnatal or post trauma. So you have two options. You can use your low contact plate, your minimally invasive or minimally disruptive approach, and/or you can use your plate as an internal external fixator. Although this concept is going out of favor because it's the danger is that you do get a mild reduction on your working neck potentially can be quite long.
Welcome to that in a moment again. And then why not use both? So that's what you're going to say in your exam. Those are my options of fixation, but an ideal plate will give me both options. Ok? then the advantages will be, of course, that you have many more options intraoperatively. But other advantages include less plates, less equipment required on your shelf, and then you've got the pre countering and countering and fracture fragment specific plates.
These are all available and there are multiple options. And at this point, I would also talk about my distal metaphyseal fixation plates, such as a distal thermal plate with an elongated shaft to allow me to do a more complex fractures. I'll talk about my individual different types of plates when my fracture fragment fits patients. But again, I want an old dancing or singing plate, and I would love a plate that will give me multiple options in one plate.
And that's where you can talk about your variable angle versus your straight locking systems and your pre-contract plates, specifically for the different types of parts of the body. And then finally, you come to your modality of use. Now Remember, I told you. I would. I would bring up modality of use at the very beginning of this conversation because depending on what you're dealing with, that's how you want to design your plate.
Ideally, even though you want an all singing, all dancing plate. There are some plates which would be inappropriate for different parts of the body versus other plates. So my approach to any fracture is what is my intention? How am I going to achieve my intention? And how am I going to hold my intention until the fractures heal, so you need to discuss things like primary healing versus secondary healing?
You need to discuss anatomical reduction versus alignment, your rigid fixation versus your relative fixation, load sharing and load bearing and combinations, as demonstrated in the picture on the right. This one definitely needs combinations of different approaches. OK so in summary, I would like to say don't jump on implants. Don't mention names of prosthesis. Don't talk about different types of names.
Don't bring up companies. The question is not about what implants. You know, it's about your understanding of the different topics within basic science. You need to understand the management principles of your fracture. You need to understand what you're trying to achieve with your fracture and what your plate is going to do to help you achieve that.
And then design your plate accordingly. OK, structure your answer. You don't have to follow this structure, but I would advise you strongly to ever think about how you're going to answer that question. And this question can easily be design your perfect hip prosthesis, design your perfect meal replacement, design your perfect intermediary rod. But it's not about which rod you know it's all about exactly what are the principles behind the design, what are the potential pitfalls and how you can avoid them?
So I want to talk about a couple of things in terms of your intention to healing and primary healing. Sorry about your modality of use. So when you put it, there is a tendency in trauma as well to put up an X-ray of a really difficult looking fracture fragment, and they'll say, how are you going to fix this? The first thing you should always say is presuming this patient has been assessed and is this is an isolated, closed injury or if they tell you it's an open injury, therefore just assume that the patient is neurovascular intact in a fully consented and draped patient.
My positioning is. And from there say, my intention of fixation will be this. My how I will achieve my goal of fixation is why and how I will maintain that fixation is the length of the construct. That's the scrub nurse. Yeah, Yeah. Yeah, Yeah. I mean, you can see some e-mails, so some do the power to it.
That's what it is. If you look at the screen is between the two nearest pins to the fracture site. Yes second set of working means that you have to think about is the bone and the bone. Yes OK. And yeah, right. So now anything else I can do to this construct that will increase rigidity and tell me why I'm back down.
About increasing the height of between the distance between your two bars, decreasing the distance from the nearest bar to the skin. We talked about multiplayer any other things you can do. Yes, I could increase the thickness of the screws or the pins. And again, that would act as the force to the third power of 3 to the power 3 pins to the power pole to 4 because it's still the cylinder shape.
Good point. In addition, I could increase the number of screws on each side, so it depends on each side. OK Yes. Yeah, you could. But do you think that's going to make a big difference? No, that's the least of all of the factors. But that adds as well. OK I could.
We've talked about I could add the thickness of the bars themselves. So instead of using a 4 millimeter or five mm, I could use a 6 millimeter. Yeah, but that's really small because we establish the distance between the bars is far more important. OK, exactly. I could use a different material. So instead of using titanium, for example, could go for stainless steel or even cobalt.
And I can or what are these, you know, nowadays? The carbon fiber? Yeah, carbon fiber. Yes and anything else? Can you do anything to the factor? Yes anatomical reduction? Well, that adds to the bone stability, and that takes some of the weight. So if you have good contact of the fracture itself, then the device would act as a load sharing love rather than a load bearing, which means the amount of forces that goes through the external fixator construct is less because of the contact between the fragments, so changing your construct to a load sharing construct would increase your rigidity overall.
Excellent I like beautiful phrasing and beautiful understanding. Excellent well done. OK, can you think of anything else about this construct which would tell you the work to make the shorter than that? If you look very closely over here.
I know I'm not getting anything. OK, so the working length of the intermediary nail is the working length, take the definition that we already presented. The definition is the unsupported length of the construct. So we have support here, correct? We also have support at the diaphysis of this femur because that is the narrowest point and we've tried to get the nail in at the size of the dialysis or just a couple of millimeters smaller than the dialysis.
Isn't that right? OK that's my 1.5 above the size of the nail that we intend to put in because we want to get it as close to it, but as big a nail as possible? OK, OK. So that's the bottom line from here to here. Not purposely put this on because I know this is a concept that sometimes we miss in our discussion of these questions.
OK so if that's the working length from here to here, what can I do to increase its this rigidity of this construct? We've already used a good thickness nail. No, we haven't, but we can use a thicker nail. Yes OK, what else? Why does that increase rigidity? It'll decrease the working length.
Not there's another more bigger factor why increasing the size of your nail the diameter, yes, to the power of the four. Is it the diameter or the radius? Really sorry. That is correct. OK anything else we can do to this, a better alignment and a better reduction of those events, exactly the same conversation we had for the external fixator.
Yes OK, Yes. What else? Going back to the methodology of this? Yes so we can use a stiffer, stiffer implant or stainless steel? OK, that's good. We can do that now. That's a question I want to ask you. Do you think this device is stainless steel or titanium and which would be your preference?
Uh, Yeah. Of titanium, because it's modulus is more closer to the bone. OK why? Why do you want to modulus closer to the bone? We are achieving a relative type of fixation in these type of fractures. So for that to get a modulus closer to the bone, the implants model is closer to the bone.
It's better. And what does that do. If you bring your implant modulus closer to the bone? No, no. OK well, what it does do is, first of all, yes, you're correct. It increases it. It becomes less rigid as a prosthesis.
So titanium is less rigid. As prosthesis, it is more flexible, but more than it has a more elastic properties to it compared to stainless steel. However it also, sorry, I just lost my train of thought. I apologize. We were talking about titanium versus stainless steel and what? Oh Yes.
So titanium has the young modulus closer to the bone, and hence it prevents stress shielding. You are using this. Thank you very much. You are using this road as a load sharing device that if you make it very rigid, it will become a load bearing device and it will create a stress shielding guys your concept needs to. Yeah so I could see 3x rays.
In this three, the first X-ray radiographs shows the fracture of a radius. Anything about that party would be a little different. So there seems to be a shot. OK good shot. Yeah, brilliant. What do you think of the. So in the second extreme, I could see that it's a lag screw, which is placed across the fracture with the neutralization plate with two screws on either side of the fracture fragment either side of a fracture.
Brilliant so what is it working like here? So this again, is a zero working Allen, because that fracture is anatomically reduced and that is a lag screw causing compression. So that will be. But this is a shaft fracture. Why are we going for anatomical and primary heating here? So the concept in both bone 4 and fractures is it is not only the I mean, this is a dangerous yes, my brain is also considered as a joint because there is a movement happening there, which is a pronation interpretation moment.
And if there is a reduction in the length of one bone, it will affect the joints proximal and distal. That is, the proximal distal radial nerve joints, which in turn will reduce the forearm pronation and supination range of motion. OK, good. So why not just put a leg screw? Do you want a neutralization plate? And what is the concept of a neutralization plate?
What does it control? OK Yeah. So, yeah, lag, screw it provides compression, but it does not have adequate bending and torsional stiffness. So to provide more bending and tonsils if we add a plate, which is a neutralization plate. Very good. You brought up the exact concepts that I wanted you to bring up bending and torsional.
So if you want to prevent, what type of plate do you want to use? So to improve the bending stiffness, I would use a blade, which is thicker with the material, which is more rigid and then. We'll OK, very good. So any other places where we would use a neutralization plate routinely?
Neutralization plates can be used everywhere, wherever we are achieving a common factual presentation that you would use a neutralization plate for. It is like an oblique fracture, but I would definitely. So what anatomical area usually the ankle? Isn't that correct? Yes Yes.
Yeah, especially on the fibula. So why? Why do we need to? Why do we use a one third tubular as a neutralization plates there compared to using a big DHCP LCP DHCP plate here? Majority of the load passes through the radius, whereas in the ankle. Majority of the load passes through the tibia of.
Good, excellent, and that's what, I don't want to hear anymore. I know, you know your stuff. You would literally. That's a minimum of a. And if we continue driving you, we probably would have got to. I think that's right.
Segment:0 .
Signs of fracture management, but specifically about plates and plate design, the reason why this is a topic that if you haven't put any thought into it when you get hit by it, you will be shocked and you will not respond well. So it's very important that we kind of go through this. It's also a great topic because it does cover quite a number of chapters in basic science and also in fracture management.
And you can take this from plate to other forms of fixation and other forms of implants, and you can use the same basic science knowledge and apply it in different ways. So I really do recommend you do spend some time focusing on this area as well. So first of all, my declarations, these are my opinions and do not represent any organization. I have no final financial interests to declare.
Pictures of implants are in no way in endorsement of any of the implants taken from the internet as fair use for educational purposes. There's our first picture design, the perfect device and your that's the response I want to try and avoid. I don't want you saying things like I use X because I perfect or I know I know it well or my hospital uses or the rep tells me it's perfect.
That you see. Remember this image of me smacking my head and getting upset with you guys? OK, so the answer is always prepare a simple sentence for any question like this. Try and divide your answers into headings and then work on those headings. So the design of my implant would require consideration of many factors, including material properties, structural properties, interface fixation and modality of use.
I would usually say modality of use. First, depending on how I'm going to use it, then I would decide what material, structural and interface fixation devices I need. But I'm leaving this to the last because it's a bigger topic and it's worth kind of quizzing you guys on it down the line. So material properties you need to discuss Young's modulus elastic plastic yield points, the brittleness or ductile features of your device, and the toughness and hardness of them.
And remember, material properties are independent of shape, so my ideal material would be something which is inert, reliable, easily manufactured and sterilized. It should be a reasonable price or a price, which is acceptable considering we put so many into them and has a corrosion resistance idea should be ductile with. We need to know how ductile we want it and the toughness and hardness.
These are two different concepts, by the way, toughness and hardness will come to that in a moment. Examples are the materials we use commonly. Stainless steel L the 3 1 six. This is quite an important question. They do ask you about this quite frequently. What does the three stands for and what? 3% nickel 16% and the L stands for low carbon, which is any metal, which any stainless steel, which has less than 0.03% Now this is quite an important concept.
Why do we use this? We won six series. So why do we use the 300 series, but specifically the L series? The reason why is the low carbon is less is more resistant to corrosion in the human body because of sodium chloride in the body. So this is a plate on metal that's been that is used in the oceans and seas by engineers there, and it has the same resistant properties as it would have in the ocean because our bodies are essentially salt. So that's quite a quick trick to that question.
But once you get that one out, you're saving yourself trouble. The next question they usually ask is what is titanium all which which we use the six Allen for the aluminium, 6% vanadium, 4% know that vanadium does have some potential iron reaction problems, and that's potentially a question that can be asked, especially if you have scratch scratches on your titanium plate or titanium rod.
But the nice thing about titanium is it's self pacifying. OK, so that's quite a useful feature of it. Other advantages with titanium is that it's Young's modulus of edges closer to bone, and therefore it's more ductile and also works better in terms of giving you work. Things like that. However, in the conversation about this, the pros and cons, you can say stainless steel has many ways of modifying its modulus of elasticity, and we've come to those questions later.
The advantage of stainless steel is it's cheap, it's readily available. We know its properties and it's consistent throughout cobalt chromium alloys, the other one we use. But in fixation, it's rare that we use it. It's more for its surface hardness that we use it for. So what is modulus of elasticity? So if you take a diagram and give yourself force in displacement, your slope gives you your stiffness.
That's force of displacement. Very simple concept. Now we're going to make it a little bit more complicated and doesn't talk about stress and strain forces. Your stresses, your force over an area which is newtons over a meter squared or otherwise known as pastels, and your strain is your change in length or height compared 2 divided by its original length, and head has no units because you're dividing distance by itself.
OK, I'm just going over this very quickly because you do need to know these definitions very well and be able to spill them out very quickly because otherwise you'll get stuck. So then taking that same diagram instead, we use stress and we change. We use the bottom to strain and we've got our slope, which is Young's modulus of elasticity. The next thing to say is that the common materials in orthopedics, there's your numbers.
Do you notice that we say titanium as a closer elastic modulus of elasticity to cortical bone? But the reality is it's a huge difference between the two. So I'm not 100% convinced this is my personal opinion. I'm 100% convinced, but titanium's advantages in these situations, especially in plates as opposed to nails. And then this diagram, it's pretty much everywhere. I do recommend you memorize it because it has come up in the exams scenarios where they've put that picture in front of you and said, what is one?
What is two one, three 4 and so on? Essentially, what they want to know is, do you understand the relative Young's modulus compared to the bone? And where would you imagine bone would be and where each of the metals and other orthopedic implant material would be? OK, now we said, we talk about a few of the properties of a stress strain graph.
And what they mean. So the elastic property is the area where Young's modulus exists, where you get an equal and straight line, essentially where you get an equal between stress and strain. And that's at this point here. After that, you get plastic deformity. And for the purposes of this, I've drawn this quite severely. Just so we can show the different parts.
So the point is the point where you move from plastic to plastic, you're yielding area is the area where you're starting to lose strength. So use hardness, but then you start to develop a strain hardening environment. This this is important to know because this is in cold, cold welding steel called working with steel. This is where you can get ultimate tensile strength in your prosthesis so you can cold work this.
What this does is it creates the undulating molecules within your stainless steel to align up more. Well and to prevent the defects and to create a more compact spacing of the molecules together. And this gives you your most, strongest or hardest material possible, but anything after a certain point, the anything after ultimate tensile strength is lacking, and we do see necking in the early stages of failure of plates and/or prostheses and finally fracture.
Now I did say I'd mentioned the difference between strength and hardness of the properties of strength and hardness. So strength is everything the surface, the area underneath that graph. So the area underneath that graph is the strength of any metal. What it represents really is the energy required to create a fracture. While the hardness is a surface property of the material, so do make sure you understand the difference between those two, and it's quite important that you want to be able to throw out those definitions very quickly.
And now so so far, we've talked about the stress strain graphs and its modality in use in orthopedics and trauma. We've also talked about the different metals we use and we've shown. Something about them and why we use different ones, you can even go through the advantages and disadvantages graph in the Ramachandran book and you'll find that the. You'll be on safe ground straightaway.
So now we go into structural properties, these include bending stiffness, bending stiffness, torsional stiffness and axilo stiffness, so bending stiffness is pretty straightforward. By the way, this is all dependent on the shape of the material. OK, so bending stiffness is essentially, if you take any length of any material and you put pressure on the whatever the length is and bend against it, that's your bending stiffness.
Social stiffness is twisting that same material and axilo stiffness is weight bearing on the length of that material. But essentially, they're all dependent on your crossbar sectional shape of your property, so your design of your implant allows resistance to bending your if, for example, if you're using a rod. If you increase the radius of the rod, you have a more straighter construct using your second moment of inertia.
That formula is pi r to the power of 4 divided by 4. And that's quite a significant number to remember because you are you literally are multiplying. If you double something, you're multiplying it by a factor of 16 of a plate or any metal bar you're talking about with multiplied by the height or, in this case, D to the power of 3. Now that's an important concept to understand, because if you ever look at building sites, you'll always see that there are girders in the building sites and you wonder why would they use girders?
Well, there you are. That's the picture that explains it perfectly there. The bottom picture here, the girder itself, you're still preserving the height of your plate. But what you're doing is using less metal. Therefore, you have a lighter construct, and it's an important concept to remember because you're maintaining the width of your construct, you're maintaining the height of your construct, but using far less metal in that process, the same principle as your Hollow nails.
Again, less for the same amount of material. You can achieve a more rigid construct by bringing out using that material as a hollow tube. You can appreciate that there's far more material in this than there is in this. And for a small decrease in the proportion of resistance sort of decrease in the proportion of your movement area. OK now, now we're going to move on to the next part of this.
Remember, we talked about using your girders as a principal and remember that their height is preserved. That's the same principle behind the low contact plate in your low contact plate. You can now take away metal. Therefore, you need less metal. But more importantly, you now have less surface area to pressure the bone. As you can see, the height is still preserved and the witness to preserve.
But the plate is missing these small areas here, which represent this area here. OK and then that same principle we talked about with the girders is still present with your one third tubular once a tubular is usually 1 millimeter thick plate. But by putting it as a one third of a tube, you're still preserving the height, as you can see on this schematic representation there.
OK now we move on to our interface fixation, so we have a choice between conventional and locking screws and the other way to describe them as is by compression and using plate friction versus a fixed angle device. OK or you can use them in combination. And the conventional plate, you're dependent on your friction interface between the plate and the bone, so what you're doing is you're compressing your plate onto the bone.
And once you've done that, your pre-loading, you're loading the bone and then the patient own load adds up together to create. Sorry, apologize. Go back. The friction force is with the is far more than the patients load, therefore your plate constructor is going to be preserved. In terms of locking platelets, graphics, you are locking your plate, your screw into the plate, that's what those crosses represent.
That's the screw locked into the plate that's creating a fixed angle device. You're loading your patient load and you're overcoming the compressive strength of the bone. OK, so essentially you're locking device is allow is transferring the weight of the bone onto the plate. So in the stress situation, you're doing your patient loading with the different types, and you have one option of preloading this and that creates your interface, so there is a difference between your standard versus locking.
Loading and. To be honest with. And then this is demonstrating that the pull out strength is each the pull out strength of this construct is dependent on a single screw each time, and each one will individually fail. One is sequentially. While what we see with the locking plates is that you get you need you have a large resistant area, but your force requires you to make sure all your fixation fixed angle fixations to fail at one go.
So there are advantages to your locking plate. However, it's not necessarily always the right answer for this, and we'll come to why that is the case. So some of the other things we need to consider about in our plate design is preservation of blood supply, and that can be a discussion about curiosity, your blood supply and the centrifugal versus centripetal of blood flow.
You may be need to talk about when those two change over both in terms of childhood and/or childhood to adulthood, and vice versa in terms of postnatal or post trauma. So you have two options. You can use your low contact plate, your minimally invasive or minimally disruptive approach, and/or you can use your plate as an internal external fixator. Although this concept is going out of favor because it's the danger is that you do get a mild reduction on your working neck potentially can be quite long.
Welcome to that in a moment again. And then why not use both? So that's what you're going to say in your exam. Those are my options of fixation, but an ideal plate will give me both options. Ok? then the advantages will be, of course, that you have many more options intraoperatively. But other advantages include less plates, less equipment required on your shelf, and then you've got the pre countering and countering and fracture fragment specific plates.
These are all available and there are multiple options. And at this point, I would also talk about my distal metaphyseal fixation plates, such as a distal thermal plate with an elongated shaft to allow me to do a more complex fractures. I'll talk about my individual different types of plates when my fracture fragment fits patients. But again, I want an old dancing or singing plate, and I would love a plate that will give me multiple options in one plate.
And that's where you can talk about your variable angle versus your straight locking systems and your pre-contract plates, specifically for the different types of parts of the body. And then finally, you come to your modality of use. Now Remember, I told you. I would. I would bring up modality of use at the very beginning of this conversation because depending on what you're dealing with, that's how you want to design your plate.
Ideally, even though you want an all singing, all dancing plate. There are some plates which would be inappropriate for different parts of the body versus other plates. So my approach to any fracture is what is my intention? How am I going to achieve my intention? And how am I going to hold my intention until the fractures heal, so you need to discuss things like primary healing versus secondary healing?
You need to discuss anatomical reduction versus alignment, your rigid fixation versus your relative fixation, load sharing and load bearing and combinations, as demonstrated in the picture on the right. This one definitely needs combinations of different approaches. OK so in summary, I would like to say don't jump on implants. Don't mention names of prosthesis. Don't talk about different types of names.
Don't bring up companies. The question is not about what implants. You know, it's about your understanding of the different topics within basic science. You need to understand the management principles of your fracture. You need to understand what you're trying to achieve with your fracture and what your plate is going to do to help you achieve that.
And then design your plate accordingly. OK, structure your answer. You don't have to follow this structure, but I would advise you strongly to ever think about how you're going to answer that question. And this question can easily be design your perfect hip prosthesis, design your perfect meal replacement, design your perfect intermediary rod. But it's not about which rod you know it's all about exactly what are the principles behind the design, what are the potential pitfalls and how you can avoid them?
So I want to talk about a couple of things in terms of your intention to healing and primary healing. Sorry about your modality of use. So when you put it, there is a tendency in trauma as well to put up an X-ray of a really difficult looking fracture fragment, and they'll say, how are you going to fix this? The first thing you should always say is presuming this patient has been assessed and is this is an isolated, closed injury or if they tell you it's an open injury, therefore just assume that the patient is neurovascular intact in a fully consented and draped patient.
My positioning is. And from there say, my intention of fixation will be this. My how I will achieve my goal of fixation is why and how I will maintain that fixation is the length of the construct. That's the scrub nurse. Yeah, Yeah. Yeah, Yeah. I mean, you can see some e-mails, so some do the power to it.
That's what it is. If you look at the screen is between the two nearest pins to the fracture site. Yes second set of working means that you have to think about is the bone and the bone. Yes OK. And yeah, right. So now anything else I can do to this construct that will increase rigidity and tell me why I'm back down.
About increasing the height of between the distance between your two bars, decreasing the distance from the nearest bar to the skin. We talked about multiplayer any other things you can do. Yes, I could increase the thickness of the screws or the pins. And again, that would act as the force to the third power of 3 to the power 3 pins to the power pole to 4 because it's still the cylinder shape.
Good point. In addition, I could increase the number of screws on each side, so it depends on each side. OK Yes. Yeah, you could. But do you think that's going to make a big difference? No, that's the least of all of the factors. But that adds as well. OK I could.
We've talked about I could add the thickness of the bars themselves. So instead of using a 4 millimeter or five mm, I could use a 6 millimeter. Yeah, but that's really small because we establish the distance between the bars is far more important. OK, exactly. I could use a different material. So instead of using titanium, for example, could go for stainless steel or even cobalt.
And I can or what are these, you know, nowadays? The carbon fiber? Yeah, carbon fiber. Yes and anything else? Can you do anything to the factor? Yes anatomical reduction? Well, that adds to the bone stability, and that takes some of the weight. So if you have good contact of the fracture itself, then the device would act as a load sharing love rather than a load bearing, which means the amount of forces that goes through the external fixator construct is less because of the contact between the fragments, so changing your construct to a load sharing construct would increase your rigidity overall.
Excellent I like beautiful phrasing and beautiful understanding. Excellent well done. OK, can you think of anything else about this construct which would tell you the work to make the shorter than that? If you look very closely over here.
I know I'm not getting anything. OK, so the working length of the intermediary nail is the working length, take the definition that we already presented. The definition is the unsupported length of the construct. So we have support here, correct? We also have support at the diaphysis of this femur because that is the narrowest point and we've tried to get the nail in at the size of the dialysis or just a couple of millimeters smaller than the dialysis.
Isn't that right? OK that's my 1.5 above the size of the nail that we intend to put in because we want to get it as close to it, but as big a nail as possible? OK, OK. So that's the bottom line from here to here. Not purposely put this on because I know this is a concept that sometimes we miss in our discussion of these questions.
OK so if that's the working length from here to here, what can I do to increase its this rigidity of this construct? We've already used a good thickness nail. No, we haven't, but we can use a thicker nail. Yes OK, what else? Why does that increase rigidity? It'll decrease the working length.
Not there's another more bigger factor why increasing the size of your nail the diameter, yes, to the power of the four. Is it the diameter or the radius? Really sorry. That is correct. OK anything else we can do to this, a better alignment and a better reduction of those events, exactly the same conversation we had for the external fixator.
Yes OK, Yes. What else? Going back to the methodology of this? Yes so we can use a stiffer, stiffer implant or stainless steel? OK, that's good. We can do that now. That's a question I want to ask you. Do you think this device is stainless steel or titanium and which would be your preference?
Uh, Yeah. Of titanium, because it's modulus is more closer to the bone. OK why? Why do you want to modulus closer to the bone? We are achieving a relative type of fixation in these type of fractures. So for that to get a modulus closer to the bone, the implants model is closer to the bone.
It's better. And what does that do. If you bring your implant modulus closer to the bone? No, no. OK well, what it does do is, first of all, yes, you're correct. It increases it. It becomes less rigid as a prosthesis.
So titanium is less rigid. As prosthesis, it is more flexible, but more than it has a more elastic properties to it compared to stainless steel. However it also, sorry, I just lost my train of thought. I apologize. We were talking about titanium versus stainless steel and what? Oh Yes.
So titanium has the young modulus closer to the bone, and hence it prevents stress shielding. You are using this. Thank you very much. You are using this road as a load sharing device that if you make it very rigid, it will become a load bearing device and it will create a stress shielding guys your concept needs to. Yeah so I could see 3x rays.
In this three, the first X-ray radiographs shows the fracture of a radius. Anything about that party would be a little different. So there seems to be a shot. OK good shot. Yeah, brilliant. What do you think of the. So in the second extreme, I could see that it's a lag screw, which is placed across the fracture with the neutralization plate with two screws on either side of the fracture fragment either side of a fracture.
Brilliant so what is it working like here? So this again, is a zero working Allen, because that fracture is anatomically reduced and that is a lag screw causing compression. So that will be. But this is a shaft fracture. Why are we going for anatomical and primary heating here? So the concept in both bone 4 and fractures is it is not only the I mean, this is a dangerous yes, my brain is also considered as a joint because there is a movement happening there, which is a pronation interpretation moment.
And if there is a reduction in the length of one bone, it will affect the joints proximal and distal. That is, the proximal distal radial nerve joints, which in turn will reduce the forearm pronation and supination range of motion. OK, good. So why not just put a leg screw? Do you want a neutralization plate? And what is the concept of a neutralization plate?
What does it control? OK Yeah. So, yeah, lag, screw it provides compression, but it does not have adequate bending and torsional stiffness. So to provide more bending and tonsils if we add a plate, which is a neutralization plate. Very good. You brought up the exact concepts that I wanted you to bring up bending and torsional.
So if you want to prevent, what type of plate do you want to use? So to improve the bending stiffness, I would use a blade, which is thicker with the material, which is more rigid and then. We'll OK, very good. So any other places where we would use a neutralization plate routinely?
Neutralization plates can be used everywhere, wherever we are achieving a common factual presentation that you would use a neutralization plate for. It is like an oblique fracture, but I would definitely. So what anatomical area usually the ankle? Isn't that correct? Yes Yes.
Yeah, especially on the fibula. So why? Why do we need to? Why do we use a one third tubular as a neutralization plates there compared to using a big DHCP LCP DHCP plate here? Majority of the load passes through the radius, whereas in the ankle. Majority of the load passes through the tibia of.
Good, excellent, and that's what, I don't want to hear anymore. I know, you know your stuff. You would literally. That's a minimum of a. And if we continue driving you, we probably would have got to. I think that's right.
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