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Free Body Diagram for Orthopaedic Exams
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Free Body Diagram for Orthopaedic Exams
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Upload Date:
2024-05-31T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
What's going to happen? Hello, everyone. Good evening, thank you, everyone, for joining us in this webinar. This is part of the teaching program we're trying to deliver to all non trainee orthopedic surgeons in the UK and overseas, preparing for the first case for us are now I work in Bristol and I'll be moderating the session, trying to help to organize it.
And you manage all your questions with the help of Sean. Our guest today is Juan, obviously, everyone knows Juan hinari, he works in banbury, in Oxford, and he's the cornerstone of our group. He's behind educational activities that we run here, and we're very privileged. He's with us. We will run the session into 30 minute blocks between each 30 minute block.
We'll have five minutes break and you have a chat option, which you can click on the bottom of the screen. That will take a chat box where you can please write all your questions, any queries you have. You want to put forward to each one, and we will try to answer this for you. Or if you have any other comments, any other technical problems, anything, feel free to write your question.
Also, raise your hand, if the issue, but the best thing is to write question. The session will be recorded. So you can all view it later on. If you have anything you want to listen to or see again, and also for the benefit of all of our colleagues on the ground, I'm not going to make any more delays. I will give the microphone now to Juan to get started. Please put your questions or comments on the chat box for me.
Thank you. OK over to you, Sean. Thank you for asking everyone, everyone, please be patient with us. We are just learning the technology now. So so far things are going quite well. We're very pleased with everything and Thanks to for us for all of this. So first of all, we're going to talk today about a free body diagram, how to draw them on some principles behind it for your exams.
The important. I do know that some of the guys have already had this presentation. We're trying to improve the presentation, but now putting it out to the whole group as a presentation. Now I'm sharing my screen with you now. Just bear with me. One second, I'll start the presentation as a slide.
Now there we go. I hope you can all see this, so everybody got diagrams for the FRC. A couple of things you need to know some principles. First of all, you do need to know about Newton's laws of motion, about inequality and remain in equilibrium unless acted on by external force. Number two, the sum of all forces on an object is equal to the mass multiplied that by the acceleration, which is force OK.
The number 3 for every force, there is an equal and opposite force on the body, provided the body is in equilibrium. OK, another thing to be aware of is weight, and we interchange weight with mass all the time and you need to know that there is a difference between the two. So weight is a force. What it is a mass by gravity, which is kilo meter per second squared.
If you think about it, gravity is an accelerating force. So it's f, which gives you your force, which is a Newton's gravity on Earth is 9.8 meters per second squared. So if you're falling from a height, you're accelerating at that speed. So to make life simple for us, we should round this all to 10 meters per second squared. So a person who has 70 kilos will have an approximate weight of 17 newtons.
Do we care? No, because we're not going to use mathematics in this way of foreign body diagrams. OK next thing is levers machine designed to move objects. It has a bar and a fulcrum. And there are three classes within the class one lever. The force and the load are on opposite sides of the fulcrum has to lever. The force is further away than the load from the fork, and one example of that is a wheelbarrow has three levers.
The force is closer to the fulcrum where the load is further away. For example, in your elbow joint with your biceps or your brachial radius so you're not breaking out. The other thing is that going to work with vectors vectors is a diplomatic representation of force. Force has a magnitude as well as direction as you can see. If you draw an arrow, the arrow indicates the magnitude and the tip of the arrow tells you the direction.
It's going OK. Shorter the arrow, the smaller the magnitude of the force, longer the arrow, the greater the magnitude of the force. The final thing we're going to need is moments, moments of a force is applied, the distance from the pivot, which causes segmental rotation. Distance is this distance is called the moment or the distance between the force and the center of rotation is the long term because the rotational effect called the turning moment and the turning moment is equivalent of force by normal time, also known as torque.
If you think about it when you're trying to screw a very tight screwdriver into your. It's like using a screwdriver into a tight bone, if you use a bigger handle screwdriver, you, you're taking, you're increasing the distance of your force away from the center of rotation. Therefore, it's easier for you to turn. So this is diagrammatic representation of this moment is equal to force by perpendicular distance from the center of rotation.
Do you guys notice that there's a small little blue line there, kind of like a right angle to angle there on the drawing that is the mathematical symbol for perpendicular angle? I'm not sure who's drawing on our screen. It's definitely not me. I apologize if that's interfering with what you're seeing. But the distance is the green dotted line from the center of rotation, and the force is.
As you can see, it's got a magnitude in the direction, but the D is perpendicular to the direction, of course. It's a very important concept to get because a lot of textbooks miss drawbacks and a lot of their descriptions. The straw that. And we are drawing so some assumptions that you need to know when you're doing this. Assumptions one is we are drawing a simplified 2D image of a complex 3D structure.
We're using vectors of moments. These are the things you must say to the examiners as you start drawing body. We draw is an equilibrium. Bones are rigid. Broad joints are frictionless, simple hinges with no antagonistic muscle actions. Weight of a body is concentrated to the center of mass internal forces.
Cancel each other out. Muscles act only intention forces or the muscle only act to the center of mass of muscle, and the joint reaction force is presumed to be compressive only if you. I know it's very hard to remember all of this, but if you start off with we're drawing simplified thing, we're using vectors and moments where our body's in equilibrium.
Usually usually it all comes to you as you're talking, so don't worry about it too much. Do you use moments? Do you use vectors? Do use magnitude and direction, resolve your vectors and draw simple diagrams to simplify your and simplify those diagrams? Don't do complex multiple lines, multiple drawings and change your levers to allow single muscle action.
A lot of people try to do multiple muscle action on a single point, so we all know the hit one. But a lot of people try to make an ankle one very complicated or a finger and very complicated unnecessarily. We won't use trigonometry, we won't use complex maths, we won't be drawing any anatomy, and we won't stop talking in the exam, ok? So that's our diagram. Just need to turn off the sharing for a moment.
Just apologize. As I said, we're just getting used to the technology now. While Sean is doing this, can I ask everyone to remember you have a chat option at the bottom of the screen? If you click on it, it will open the chat box. You could put your questions here and it really is anything that you want more to be clarified or any comments, you could put them here, and I will bring them across to Sean to remember the chat option at the bottom of the screen.
You can click on the chat box. OK, so the sharing is off yet. You can see me again now. I'm just going to go to a different device, which will allow me to draw for you while we discuss all of this, ok? No sharing is not off.
You we can see your computer share. Yeah, I appreciate that I'm sorry, I'm just having trouble are. I'm sorry about that. The so just going to move to a different device for sharing, we should now all see a whiteboard on your screen.
OK, so I'm going to go back to the one that is most commonly asked, which is the hip. But there are variations of all of this, and it's very important to understand all of this. OK, so first of all, do not draw complex anatomy. So the best way to draw this is to draw just a simple line diagram. OK OK, so that's my hip.
Everyone agree that that's a right hip. There's no issues in that question there right now. So what we then do is we I'm going to change colors so that we have a different. On full force is. And what we then do is draw w- As a very small force, OK, remember, this is a vector, so vectors have magnitude and direction, weight is going down.
We're talking mutants here, but don't stress about numbers or anything like that. I'm making a very small arrow. It's very important that you always keep your W small. The weight very small. Then we are going to draw an abductor force, which is going to go in this direction. And you do notice it's quite large.
Then I'm just going to change the color to light blue so we can do our moment arms. And through the center of rotation. We go perpendicular, and that's the mathematical symbol for perpendicular. Ok? and again, the same perpendicular to the direction of force.
You all appreciate that, because what tends to happen is that when you read the textbooks or when people draw, they tend to do that. That is incorrect, ok? It has to be a perpendicular force and you will be caught out if you don't do this. So what I always do is I always take the smallest line and give it a alphabetical designation.
So this is the force between the center of rotation is between and the 4 and the force of the adductors. I draw, I write it as a small D then because I know actually what is the answer here? I'm just going to say, well, this looks like one d, the distance between central location and you looks like 5D. Does that make sense? So then what we then do is go F. Multiplied by D is equal to.
5 3 multiplied by w if you cancel out, the force of the adductors is equal to 5 times the body weight. And then if the examiners insist on a number and say, well, the person's brain is 70, then you say it's five times 70 and they want to get if you want them to give you a number, just tell them, give me a calculator. You don't need mathematics for this.
You don't need complex trigonometry. Now, the reason why you don't need complex trigonometry here is because what we're going to do is resolve for the foreseeable vectors here. OK, so if we draw this as a parallelogram, what we then do is draw air. You don't do that, just apologize or go back to doing this is a green line.
And do you notice what I'm doing is I'm transferring this air, I'm moving it away from there, but keeping it parallel and the same magnitude. Forgive my artistic lack of artistic abilities, but that's what I'm doing. What I then do is I take the W and add it onto the tip of the F. Tale starts on the tip of the hat.
And the same parallel and the same length. OK, so if this is 5 w, this is w because we know F is equal to five, w is not right. We then take joint reaction force must be going from the W to the tale of a. And here is some guesswork presume that this is half the length of a W So then this is 5 and 1/2 times W That's our joint reaction force.
Two and then all you do is transfer that over to this side and you've got your joint reaction force there. We're going to take a second piece of paper and use that as your ruler type thing if you really want it, but you don't need to be very accurate here, what you're showing is the concept. You understand this concept. OK, everyone. If everyone's happy with that and I'll take questions on the next session.
So we can come back to this, we'll just erase all of this. And we start again now with a different concept. So I'm going to go to the more difficult ones, by the way, on the hit, I'm very sure that you can all resolve this easily for. I'm very sure you can always all easily that you can work out if the person is using a stick on the opposite side of the head, therefore that force is going up and therefore on the lever.
It's actually decreasing the joint reaction force overall because the abductors work less. The whole point is because the abductors are working so hard, they're causing a massive joint reaction force to take off the weight of the adductors we can. Then we can decrease joint reaction force. We can come back to that in the next section. I just want to move on to a little bit more complicated ones, which people seem to always have a lot of trouble with the ankle.
What we'll do is when we use red as our primary color for tenotomy. OK so with the ankle. People tend to draw the ankle as a flood situation, I don't what I do is I tell the examiner straightaway that I am drawing the person standing on tiptoe. OK if that's the person standing on tiptoe, this is the ground. And if that is the case, this is the uncle is here.
This is Bianca, correct? So if you remember Newton's third law, this patient is in equilibrium and he's balancing on his tiptoes, his entire weight is now going through the toes, touching the ground for every action. There is an opposite and there's an equal and opposite reaction. Therefore, if the body weight of the patient is going all the way through the tiptoes and down, we need to switch to 10.
We need to get. If that's w. There must be an equal and opposite reaction, so therefore there must be a ground reaction force equal and opposite on this patient because he is this person because he's balanced. OK, so grief is going up. Correct now, what is counteracting the force of the group push to push this put up is the force of the Achilles tendon.
So if we draw the Achilles tendon as a large force? That's the force of the Achilles tendon. Now you can appreciate now we have the ankle as our fulcrum, and this is now a simple type 1 lever as opposed to what tends to happen, is people try to put the center of gravity in an unusual place or put the patient on flat foot. And then you have to engage tip arms and Achilles tendon in the balance process.
And of course, you're standing on a tripod as opposed to a single point. You make life easier. You're now moving to a single lever and you just turn the hip upside down. That's what you've done. Does that make sense? OK, so now once again, if you switch to blue to draw our momentum, pretty sure you go best, but our only two arms are going to be.
That's momentum for the ground reaction force and everyone, everyone kind of looks well, it's not interacting with the actual force. Yes, it is. If you just go and imagine this line continuing up, there is your reaction reaction force. This is in line in perpendicular to the line of direction of the force that you're measuring.
OK, your ground reaction force for the Achilles. Is here so your momentum for your tenodesis here. Now, if we again take the smaller line and take it as de. This must be for the. OK, so once again, resolving what we get is if. Baiji is equal to 4. The f, since we know that grief is w.
Or we have to then say is for. Wf is equal to 4 w. OK, now the next question they're going to ask you is so the force going into these is 4 times W The next question we're going to ask you is, can you resolve the show is what the joint reaction force is. So if you take f as your first round, you move it away to the side and go to hear f.
Everyone agree that it's close to exactly the same size and line, then from tale of from the tip of at the tail of ground reaction force. So that's g. Rf, which we know is w, and this is w then the most because this is an equilibrium, there must be an equal and opposite reaction from the joint, the joint reaction force. And all you have to do is add the tip or so from the tip of graph down to the tail of f.
Of course. The reason why I'm drawing them next to each other is because if I draw them on top of each other, you can't see what's going on, but all I'm doing is drawing one line on top of the other. Does that make sense? And this is my joint reaction force. And if you add these two, if this is w equals ground reaction force, what you get is equal to D5W and then all you do is draw that here.
Now, of course, my paper is too small, but you can appreciate that is my joint reaction force D5W. OK everyone, I know there is no interaction at the moment, if you have questions, please take them for later. I'm just going to go on to the we have time for us to go to the next topic next. I think if you're going to start a new topic.
Better to leave it to the next block. We could allow enough time for questions. There have been some private questions sent to me. The minor issues, but if anyone has. Any questions and you want to talk and speak to Sean directly about it? Just raise your hand. Next to your name on the list of participants and I could make you active so you can talk and speak to 1 or the other option is you could write your question down.
So on the question at the moment. OK OK, shall we? How many minutes is left on this session? We have. We have about just over five minutes. OK in that case, what I would do is just quickly draw the hips. While we have those five minutes, OK, we got the hit for one moment and we'll show you how it goes here.
What you can do with the hip to try and show that. How to decrease joint reaction force.
OK very quick, rudimentary drawing there. If the person takes a stick on his opposite hand, but we then have is a force going up in this direction, so this is, we call it as caustic. If a person is carrying a weight on the opposite hand, we have a. Back in the opposite town, that's be all you can do is sum up the situation. So this is, we said, five days.
This must be the number five days between the tweets and say, so what to just resolve for this area? So just to resolve for the stick in the hand, what we can do is D is equal to 5 dw plus. The 10 the. Does that make sense? So then if we take away these.
We have 5 equal to D5W plus tens. Now you can see that the force required for the abductors is going to need sorry minus as my apologies should have been mine from the beginning. Did I just erase everything? And we've run out of time. OK, we're. So we haven't gone out. I thought it's just not there for us.
That should be a minus because if you can see this is going in the opposite direction or W so therefore it's push up the c, so on the W side, push up the liberal side. So that should be a minus. So if. Plus, tens because we now move it over to the other side is equal to D5W.
And as you can see that wef is now you need to be much smaller in size. But the reality is what we then do is we make the vector much smaller. You don't need to draw all this out. You just say the stick on the opposite side. And this is the reason why, because the force will go in the opposite direction of the weight is some of the weight is now supported by the stick.
Therefore, the forces of the adductors are decreased. Therefore, overall, the joint reaction force will decrease because there's less force going through the joint because Earth is much smaller. It's the same with the bag on the other side. You just have to say that because the patient is carrying the weight on the other side. The doctors don't need to work. So hard to keep the patient balanced.
Therefore, they're much smaller forces. Therefore, there's less joint reaction force. I know it's counterintuitive because the patient is carrying more weight, but what? What you have to remember is at that moment when that patient is standing on one leg on that hip. This is not a situation where all the weight is going through the hip. It's the situation where the forces are being balanced on a seesaw between the two.
And therefore, if you can make the seesaw more balanced on one side or the other, you decrease the forces going through the hip by decreasing the abductor force. OK that was wonderful show, and thank you very much for all the efforts we put so far. We will guys everyone. We will have a break of five minutes so you can relax and stretch. I will send another link through the WhatsApp group to join the next session next block, where everyone is going to tell us all about the rest of the more tricky joints and the more detailed explanation of free body diagram of different joints and would also, we really need to have questions and comments from you, mainly to know that everything is clear to know your views.
You have the reaction from you just to know how things are. How are you getting on? So we need to have your comments and questions, please. So that will help us a lot to proceed with the session today. So I will log off now and the meeting, and I will send you another link you have five minutes for everyone to have a break to see you in five minutes.
Segment:0 .
What's going to happen? Hello, everyone. Good evening, thank you, everyone, for joining us in this webinar. This is part of the teaching program we're trying to deliver to all non trainee orthopedic surgeons in the UK and overseas, preparing for the first case for us are now I work in Bristol and I'll be moderating the session, trying to help to organize it.
And you manage all your questions with the help of Sean. Our guest today is Juan, obviously, everyone knows Juan hinari, he works in banbury, in Oxford, and he's the cornerstone of our group. He's behind educational activities that we run here, and we're very privileged. He's with us. We will run the session into 30 minute blocks between each 30 minute block.
We'll have five minutes break and you have a chat option, which you can click on the bottom of the screen. That will take a chat box where you can please write all your questions, any queries you have. You want to put forward to each one, and we will try to answer this for you. Or if you have any other comments, any other technical problems, anything, feel free to write your question.
Also, raise your hand, if the issue, but the best thing is to write question. The session will be recorded. So you can all view it later on. If you have anything you want to listen to or see again, and also for the benefit of all of our colleagues on the ground, I'm not going to make any more delays. I will give the microphone now to Juan to get started. Please put your questions or comments on the chat box for me.
Thank you. OK over to you, Sean. Thank you for asking everyone, everyone, please be patient with us. We are just learning the technology now. So so far things are going quite well. We're very pleased with everything and Thanks to for us for all of this. So first of all, we're going to talk today about a free body diagram, how to draw them on some principles behind it for your exams.
The important. I do know that some of the guys have already had this presentation. We're trying to improve the presentation, but now putting it out to the whole group as a presentation. Now I'm sharing my screen with you now. Just bear with me. One second, I'll start the presentation as a slide.
Now there we go. I hope you can all see this, so everybody got diagrams for the FRC. A couple of things you need to know some principles. First of all, you do need to know about Newton's laws of motion, about inequality and remain in equilibrium unless acted on by external force. Number two, the sum of all forces on an object is equal to the mass multiplied that by the acceleration, which is force OK.
The number 3 for every force, there is an equal and opposite force on the body, provided the body is in equilibrium. OK, another thing to be aware of is weight, and we interchange weight with mass all the time and you need to know that there is a difference between the two. So weight is a force. What it is a mass by gravity, which is kilo meter per second squared.
If you think about it, gravity is an accelerating force. So it's f, which gives you your force, which is a Newton's gravity on Earth is 9.8 meters per second squared. So if you're falling from a height, you're accelerating at that speed. So to make life simple for us, we should round this all to 10 meters per second squared. So a person who has 70 kilos will have an approximate weight of 17 newtons.
Do we care? No, because we're not going to use mathematics in this way of foreign body diagrams. OK next thing is levers machine designed to move objects. It has a bar and a fulcrum. And there are three classes within the class one lever. The force and the load are on opposite sides of the fulcrum has to lever. The force is further away than the load from the fork, and one example of that is a wheelbarrow has three levers.
The force is closer to the fulcrum where the load is further away. For example, in your elbow joint with your biceps or your brachial radius so you're not breaking out. The other thing is that going to work with vectors vectors is a diplomatic representation of force. Force has a magnitude as well as direction as you can see. If you draw an arrow, the arrow indicates the magnitude and the tip of the arrow tells you the direction.
It's going OK. Shorter the arrow, the smaller the magnitude of the force, longer the arrow, the greater the magnitude of the force. The final thing we're going to need is moments, moments of a force is applied, the distance from the pivot, which causes segmental rotation. Distance is this distance is called the moment or the distance between the force and the center of rotation is the long term because the rotational effect called the turning moment and the turning moment is equivalent of force by normal time, also known as torque.
If you think about it when you're trying to screw a very tight screwdriver into your. It's like using a screwdriver into a tight bone, if you use a bigger handle screwdriver, you, you're taking, you're increasing the distance of your force away from the center of rotation. Therefore, it's easier for you to turn. So this is diagrammatic representation of this moment is equal to force by perpendicular distance from the center of rotation.
Do you guys notice that there's a small little blue line there, kind of like a right angle to angle there on the drawing that is the mathematical symbol for perpendicular angle? I'm not sure who's drawing on our screen. It's definitely not me. I apologize if that's interfering with what you're seeing. But the distance is the green dotted line from the center of rotation, and the force is.
As you can see, it's got a magnitude in the direction, but the D is perpendicular to the direction, of course. It's a very important concept to get because a lot of textbooks miss drawbacks and a lot of their descriptions. The straw that. And we are drawing so some assumptions that you need to know when you're doing this. Assumptions one is we are drawing a simplified 2D image of a complex 3D structure.
We're using vectors of moments. These are the things you must say to the examiners as you start drawing body. We draw is an equilibrium. Bones are rigid. Broad joints are frictionless, simple hinges with no antagonistic muscle actions. Weight of a body is concentrated to the center of mass internal forces.
Cancel each other out. Muscles act only intention forces or the muscle only act to the center of mass of muscle, and the joint reaction force is presumed to be compressive only if you. I know it's very hard to remember all of this, but if you start off with we're drawing simplified thing, we're using vectors and moments where our body's in equilibrium.
Usually usually it all comes to you as you're talking, so don't worry about it too much. Do you use moments? Do you use vectors? Do use magnitude and direction, resolve your vectors and draw simple diagrams to simplify your and simplify those diagrams? Don't do complex multiple lines, multiple drawings and change your levers to allow single muscle action.
A lot of people try to do multiple muscle action on a single point, so we all know the hit one. But a lot of people try to make an ankle one very complicated or a finger and very complicated unnecessarily. We won't use trigonometry, we won't use complex maths, we won't be drawing any anatomy, and we won't stop talking in the exam, ok? So that's our diagram. Just need to turn off the sharing for a moment.
Just apologize. As I said, we're just getting used to the technology now. While Sean is doing this, can I ask everyone to remember you have a chat option at the bottom of the screen? If you click on it, it will open the chat box. You could put your questions here and it really is anything that you want more to be clarified or any comments, you could put them here, and I will bring them across to Sean to remember the chat option at the bottom of the screen.
You can click on the chat box. OK, so the sharing is off yet. You can see me again now. I'm just going to go to a different device, which will allow me to draw for you while we discuss all of this, ok? No sharing is not off.
You we can see your computer share. Yeah, I appreciate that I'm sorry, I'm just having trouble are. I'm sorry about that. The so just going to move to a different device for sharing, we should now all see a whiteboard on your screen.
OK, so I'm going to go back to the one that is most commonly asked, which is the hip. But there are variations of all of this, and it's very important to understand all of this. OK, so first of all, do not draw complex anatomy. So the best way to draw this is to draw just a simple line diagram. OK OK, so that's my hip.
Everyone agree that that's a right hip. There's no issues in that question there right now. So what we then do is we I'm going to change colors so that we have a different. On full force is. And what we then do is draw w- As a very small force, OK, remember, this is a vector, so vectors have magnitude and direction, weight is going down.
We're talking mutants here, but don't stress about numbers or anything like that. I'm making a very small arrow. It's very important that you always keep your W small. The weight very small. Then we are going to draw an abductor force, which is going to go in this direction. And you do notice it's quite large.
Then I'm just going to change the color to light blue so we can do our moment arms. And through the center of rotation. We go perpendicular, and that's the mathematical symbol for perpendicular. Ok? and again, the same perpendicular to the direction of force.
You all appreciate that, because what tends to happen is that when you read the textbooks or when people draw, they tend to do that. That is incorrect, ok? It has to be a perpendicular force and you will be caught out if you don't do this. So what I always do is I always take the smallest line and give it a alphabetical designation.
So this is the force between the center of rotation is between and the 4 and the force of the adductors. I draw, I write it as a small D then because I know actually what is the answer here? I'm just going to say, well, this looks like one d, the distance between central location and you looks like 5D. Does that make sense? So then what we then do is go F. Multiplied by D is equal to.
5 3 multiplied by w if you cancel out, the force of the adductors is equal to 5 times the body weight. And then if the examiners insist on a number and say, well, the person's brain is 70, then you say it's five times 70 and they want to get if you want them to give you a number, just tell them, give me a calculator. You don't need mathematics for this.
You don't need complex trigonometry. Now, the reason why you don't need complex trigonometry here is because what we're going to do is resolve for the foreseeable vectors here. OK, so if we draw this as a parallelogram, what we then do is draw air. You don't do that, just apologize or go back to doing this is a green line.
And do you notice what I'm doing is I'm transferring this air, I'm moving it away from there, but keeping it parallel and the same magnitude. Forgive my artistic lack of artistic abilities, but that's what I'm doing. What I then do is I take the W and add it onto the tip of the F. Tale starts on the tip of the hat.
And the same parallel and the same length. OK, so if this is 5 w, this is w because we know F is equal to five, w is not right. We then take joint reaction force must be going from the W to the tale of a. And here is some guesswork presume that this is half the length of a W So then this is 5 and 1/2 times W That's our joint reaction force.
Two and then all you do is transfer that over to this side and you've got your joint reaction force there. We're going to take a second piece of paper and use that as your ruler type thing if you really want it, but you don't need to be very accurate here, what you're showing is the concept. You understand this concept. OK, everyone. If everyone's happy with that and I'll take questions on the next session.
So we can come back to this, we'll just erase all of this. And we start again now with a different concept. So I'm going to go to the more difficult ones, by the way, on the hit, I'm very sure that you can all resolve this easily for. I'm very sure you can always all easily that you can work out if the person is using a stick on the opposite side of the head, therefore that force is going up and therefore on the lever.
It's actually decreasing the joint reaction force overall because the abductors work less. The whole point is because the abductors are working so hard, they're causing a massive joint reaction force to take off the weight of the adductors we can. Then we can decrease joint reaction force. We can come back to that in the next section. I just want to move on to a little bit more complicated ones, which people seem to always have a lot of trouble with the ankle.
What we'll do is when we use red as our primary color for tenotomy. OK so with the ankle. People tend to draw the ankle as a flood situation, I don't what I do is I tell the examiner straightaway that I am drawing the person standing on tiptoe. OK if that's the person standing on tiptoe, this is the ground. And if that is the case, this is the uncle is here.
This is Bianca, correct? So if you remember Newton's third law, this patient is in equilibrium and he's balancing on his tiptoes, his entire weight is now going through the toes, touching the ground for every action. There is an opposite and there's an equal and opposite reaction. Therefore, if the body weight of the patient is going all the way through the tiptoes and down, we need to switch to 10.
We need to get. If that's w. There must be an equal and opposite reaction, so therefore there must be a ground reaction force equal and opposite on this patient because he is this person because he's balanced. OK, so grief is going up. Correct now, what is counteracting the force of the group push to push this put up is the force of the Achilles tendon.
So if we draw the Achilles tendon as a large force? That's the force of the Achilles tendon. Now you can appreciate now we have the ankle as our fulcrum, and this is now a simple type 1 lever as opposed to what tends to happen, is people try to put the center of gravity in an unusual place or put the patient on flat foot. And then you have to engage tip arms and Achilles tendon in the balance process.
And of course, you're standing on a tripod as opposed to a single point. You make life easier. You're now moving to a single lever and you just turn the hip upside down. That's what you've done. Does that make sense? OK, so now once again, if you switch to blue to draw our momentum, pretty sure you go best, but our only two arms are going to be.
That's momentum for the ground reaction force and everyone, everyone kind of looks well, it's not interacting with the actual force. Yes, it is. If you just go and imagine this line continuing up, there is your reaction reaction force. This is in line in perpendicular to the line of direction of the force that you're measuring.
OK, your ground reaction force for the Achilles. Is here so your momentum for your tenodesis here. Now, if we again take the smaller line and take it as de. This must be for the. OK, so once again, resolving what we get is if. Baiji is equal to 4. The f, since we know that grief is w.
Or we have to then say is for. Wf is equal to 4 w. OK, now the next question they're going to ask you is so the force going into these is 4 times W The next question we're going to ask you is, can you resolve the show is what the joint reaction force is. So if you take f as your first round, you move it away to the side and go to hear f.
Everyone agree that it's close to exactly the same size and line, then from tale of from the tip of at the tail of ground reaction force. So that's g. Rf, which we know is w, and this is w then the most because this is an equilibrium, there must be an equal and opposite reaction from the joint, the joint reaction force. And all you have to do is add the tip or so from the tip of graph down to the tail of f.
Of course. The reason why I'm drawing them next to each other is because if I draw them on top of each other, you can't see what's going on, but all I'm doing is drawing one line on top of the other. Does that make sense? And this is my joint reaction force. And if you add these two, if this is w equals ground reaction force, what you get is equal to D5W and then all you do is draw that here.
Now, of course, my paper is too small, but you can appreciate that is my joint reaction force D5W. OK everyone, I know there is no interaction at the moment, if you have questions, please take them for later. I'm just going to go on to the we have time for us to go to the next topic next. I think if you're going to start a new topic.
Better to leave it to the next block. We could allow enough time for questions. There have been some private questions sent to me. The minor issues, but if anyone has. Any questions and you want to talk and speak to Sean directly about it? Just raise your hand. Next to your name on the list of participants and I could make you active so you can talk and speak to 1 or the other option is you could write your question down.
So on the question at the moment. OK OK, shall we? How many minutes is left on this session? We have. We have about just over five minutes. OK in that case, what I would do is just quickly draw the hips. While we have those five minutes, OK, we got the hit for one moment and we'll show you how it goes here.
What you can do with the hip to try and show that. How to decrease joint reaction force.
OK very quick, rudimentary drawing there. If the person takes a stick on his opposite hand, but we then have is a force going up in this direction, so this is, we call it as caustic. If a person is carrying a weight on the opposite hand, we have a. Back in the opposite town, that's be all you can do is sum up the situation. So this is, we said, five days.
This must be the number five days between the tweets and say, so what to just resolve for this area? So just to resolve for the stick in the hand, what we can do is D is equal to 5 dw plus. The 10 the. Does that make sense? So then if we take away these.
We have 5 equal to D5W plus tens. Now you can see that the force required for the abductors is going to need sorry minus as my apologies should have been mine from the beginning. Did I just erase everything? And we've run out of time. OK, we're. So we haven't gone out. I thought it's just not there for us.
That should be a minus because if you can see this is going in the opposite direction or W so therefore it's push up the c, so on the W side, push up the liberal side. So that should be a minus. So if. Plus, tens because we now move it over to the other side is equal to D5W.
And as you can see that wef is now you need to be much smaller in size. But the reality is what we then do is we make the vector much smaller. You don't need to draw all this out. You just say the stick on the opposite side. And this is the reason why, because the force will go in the opposite direction of the weight is some of the weight is now supported by the stick.
Therefore, the forces of the adductors are decreased. Therefore, overall, the joint reaction force will decrease because there's less force going through the joint because Earth is much smaller. It's the same with the bag on the other side. You just have to say that because the patient is carrying the weight on the other side. The doctors don't need to work. So hard to keep the patient balanced.
Therefore, they're much smaller forces. Therefore, there's less joint reaction force. I know it's counterintuitive because the patient is carrying more weight, but what? What you have to remember is at that moment when that patient is standing on one leg on that hip. This is not a situation where all the weight is going through the hip. It's the situation where the forces are being balanced on a seesaw between the two.
And therefore, if you can make the seesaw more balanced on one side or the other, you decrease the forces going through the hip by decreasing the abductor force. OK that was wonderful show, and thank you very much for all the efforts we put so far. We will guys everyone. We will have a break of five minutes so you can relax and stretch. I will send another link through the WhatsApp group to join the next session next block, where everyone is going to tell us all about the rest of the more tricky joints and the more detailed explanation of free body diagram of different joints and would also, we really need to have questions and comments from you, mainly to know that everything is clear to know your views.
You have the reaction from you just to know how things are. How are you getting on? So we need to have your comments and questions, please. So that will help us a lot to proceed with the session today. So I will log off now and the meeting, and I will send you another link you have five minutes for everyone to have a break to see you in five minutes.
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