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Examples of Free Body Diagram for Orthopaedic Exams
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Examples of Free Body Diagram for Orthopaedic Exams
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Language: EN.
Segment:0 .
OK, everyone. Thank you, everyone, to everyone who has come back. Thanks, Juan. Give us give us very good introduction to the principles behind free diagrams and hip and ankle diagrams drawings. He's going to continue now with next half an hour with more.
More joints. And please, please keep your comments and questions coming. I just have to let you know. After this session, we will carry on a small Viva session for people who want to be take a hot seat on. Or people who just want to watch. But that would be after this next block over. Guys who are going to sit there for three repeating this for some of you guys.
So it's worth giving you something else as well. OK thank you, Ferre. Over to you. OK thank you for us. The so we discussed hips, we discussed ankle, I showed you how you can chair the class one levers are easiest ones to resolve. And I showed you how you can change an Ankle to cast one lever as well.
There's another class one lever in the body. There's actually two more class one levers that you should pretty well. Ok? the first one is the spine purposely going to difficult ones. Everyone tends to think that these difficult ones are really hard. They're not.
They're very straightforward, very easy. Nothing to worry about. So for the spine, what I would do is I would draw to declare two motion segments of the spine. Essentially, this is two vertebrae. And the way I would describe this to the examiner, apart from talking about all my assumptions which we discussed earlier on, I would say this person is leaning forward.
OK so I appreciate that this drawing is like leaning forward, but it's just easier to draw it this way using this whiteboard. So imagine this person is leaning forward and the person is leaning forward. Then what we have is the person's whole weight, and he's carrying the weight as well. Let's presume he's carrying the box with arms straight and leaning forward, so he's hanging down.
So the whole weight of the body and the weight of the box all combined gives you a force of w. Just W just there. OK OK, so what's counteracting this force? Remember, our center of gravity is our center rotation is the disk.
And are interesting and quite badly. As I said, I'm not used to this. There this. OK, so our center is the middle of that desk, so what's the forces that are going there are the spinal muscles, ok? They are then creating a. Forced in the opposite direction.
And then we're assuming this patient is meaning. OK so this force is. So then we just do the same thing that we get, everyone else is type I cast one lever, so there's nothing special about it. We just change the color to you. You can see the moments on.
And I suspect all of you have already kind of worked out how to draw this. If you raise this up to date and then this one is perpendicular again. And remember, this is a mathematical symbol for perpendicular. OK, so even if you're not going perpendicular, if you draw that and say it's perpendicular, the examiners have to accept it because you were saying momentum is perpendicular to the direction of.
OK, so if we say this is D. The shortest one is the and then just take that as a multiple of these in this case, a the reality is in real life, you're drawing something like five or 60, but it's very hard to draw this on a small piece of paper then resolving our forces we've got. By D equals, we BW cancel out Kessler suture degrees F is equal 3 times weight.
In this case, weight includes the weight of what the person is carrying. OK, so what's our joint reaction force? So again, it's the same thing. It's a type I either. All you need to do is just add these legs together. And then do an equally opposite reaction force. OK, so once again. I would agree that is where it should be parallel.
And then just add another line down there, and then of course, these are the arrows. So this is w And this is. And then you go from tip of arrow, you add the tail to the tip of the arrow to the tail of the last, the first arrow.
And that's our joint reaction force. OK again, if you say this is 3-d, this is w if we w apologize w tenodesis w, you can presume that you can take a guesswork with jerk reaction force equal to 3 and 1/2 times right now. Please be aware. You should draw this really big exam and don't use 3D as your. No, it should be something around the line or five or 60 because the weight your body weight is actually very far away from the center of rotation.
You're leaning forward compared to your spinal muscles, the muscles that are erect and so on. OK does that make sense? So do your line. But I'm just showing you. It's just a simple class form again. OK the next one with some examiners asked about the weight of the head on the cervical spine and how it affects the T2 C2.
OK, so once again, just simple diagram, nothing fancy. Don't be a hero. Don't do anything foolish. Just do a simple diagram. So circle for a head. OK, I'd like to draw my circle like an egg to represent the skull.
The simple rectangle for your. The spine. And say your center of gravity, so your center of rotation, your function is just there, ok? That's that's it. That's all it is. OK, so once you've done that, you can then take your weight again.
OK and then again, the muscles at the back of your neck. OK and once again, it's a type class one labor type, class one labor.
There's your. Two different forces, if that's D And that's d, then fd equals dw. Therefore, F is equal to the weight of the stock. Simple as that. Of course, again, you could make a 2 day as in the wake of your patient is leaning forward, so therefore the weight is far more forward.
So you make it to can say that in the exam if you wish to say that. OK, so and then now to calculate your joint reaction force here, then it's just add the F vector F. To vector W OK in this case, because we've decided the FMW are the same size, let's just redraw that as FMW. Then you don't reaction force is equal to. To w.
Does that makes sense, I hope everyone understands this. Look again, if you do decide that you are leaning the head forward and I would advise you to do that, make your W far more forward and say it's too D as opposed to distances 2 times D OK, so therefore you can then get F is equal to 2 w, then your joint reaction force will be f-ing.
Joint reaction force will be equal to 3w. OK you are. I'm sorry, I just want to make sure you'll understand when you're drunk, when you're drawing pictures, when you're adding vectors, you add them in the way you would add a parallelogram. But what we're doing is we're taking a little cheat instead of doing parallel.
We're doing a triangle and just to show you what I mean. If I take a line. And just like that. Take another line like that, and I want to resolve the forces on this point here. These are two forces. If I want to resolve these two forces on this point here, I then draw a parallel line like this. There, which is the equivalent of x, and this is why I draw another line parallel, which is why.
OK does that make sense? This is something for want of a better way of saying it and why can't? What we then have is. The sum of these two vectors is in this direction. These two forces are working in this way. And you can appreciate. It's quite a large vector. Magnitude is increased, as you can see.
And also the force direction is increased. So what we're really doing here is we're just not including this part. All we're doing is a triangle. So we're adding this force and then we're taking the next triangle and taking it. Sorry, I didn't make myself myself. So we're taking this course. Adding another force this way, because we want to talk about opposite and equal reaction that sum of these two forces must give you an opposite reaction in this direction.
Does that make sense? OK, so you all understand how to add vectors in this way? OK OK. Sean, what are you talking about this? I had a good question coming through just a bit more expansion on the hip free body diagram and a little bit more explanation from you on how they're using a stick affects the joint reaction forces.
How is the difference between using stick on one hand on the, you know, the affected side versus using it on the contralateral side? And how does this affect joint reaction forces? If you could briefly touch on that, let me just quickly draw the hip again. OK so. If if this is the person's weight.
W and we have abductors going here. Yeah if the patient is carrying a stick on the opposite side. That's the force of the stick. Yes OK, so then what happens here is if you take the moment of those two forces, if you think about it, this is a seesaw. So if I draw you a seesaw? There you are.
This is a seesaw. This is the abductor force doing this to this, and this is the weight of the person doing that. And this is the stick doing that. As you can see, the two forces that are working together is. And yes, they're on the same side, they're trying to rotate the seesaw anticlockwise. The only thing that's working clockwise is w.
OK, so this is what we're essentially resolving here, we resolving those forces. So if you imagine if you take f as your force abductor and you add s to it. You don't need a lot of f, you don't need a lot of adapter for us to counteract the effect of your body weight because you have as helping you. Isn't that right? But if you have no S if.
This is absent, then, yes, you do need quite a large. You do need quite a large and I do appreciate that I've drawn the distance is wrong, but I just wanted to show you the principle of a seesaw here. That's what we call a type I lever. So if you type 1 lever is in balance, then all forces must be resolved in equal within. And if you put your stick on the opposite side, so if you have a stick here on this side.
Instead, OK, let's call this again, I appreciate I'm not going to back those on the right side, but I just want to be able to see them. So let's put that S on this C So here. And then you can see that as here wants to help the weight. So what's happening is she wants to change the direction to clockwise, it wants to flip the seesaw clockwise and the only m.w., so they're working together, while f is the only force that's working anti-clockwise.
So this is all in balance, then F is equal to w plus s. OK, because the reality is f-minus asked initially, and then you take over the house to the other side and F is equal to. Does that make sense? OK, so you can appreciate the F here who is working far more hard or your abductors are working far more harder.
And if your abductors are working far more harder, then far larger magnitude of a vector. And if it's a far larger magnitude of a vector, you have to add a W on to that. And of course, you've minus the bit of s away, and now you've got a far larger joint reaction force. I hope that explains it, why you need to stick it on the side. This one that explains it very well, thank you.
I had another question. Schwann different type of lever is the shoulder joint and people want to hear from you. How would you draw a shoulder free body diagram? OK, so these are the other levers that we need to move on to. That's correct. OK, so let's talk about the shoulder. All right.
So we'll start with that one. Once again, let's remember we're not doing anatomy, and you must talk about your assumptions when you're drawing. OK, so the best thing to do with this is everyone thinks that they need to draw the shoulder down. The problem with that is then you've got more complex muscles active in that situation, then you really need and you're now finding it very hard to find out where the direction of your biggest muscle your deltoid is going because you can appreciate your deltoid just now working as a 90 degree angle muscle as opposed to if you put it up here, it's not working as a contraction muscle.
Does that make sense? So the best thing to do is draw your shoulder perpendicular to parallel to the ground or just close to parallel to the ground. So if we take a. The small oval to show the humeral head to a line. Before the humerus or the arm. And draw the circle to represent the glenoid. No, that's all you need to draw for all of this.
You just say that the ground the arm is held out, it's almost parallel to the ground. Then you put the weight of the whole arm through the center of the arm in this case will put it very close to the edge so that you can see the difference. That's w. And then what you then now need to worry about is your deltoid, so your deltoid is a large force.
In this direction. OK does that make sense? Can everyone appreciate that the deltoid is now working in that direction if you go through the cross section of the muscle? So now what we need to do is. So what type of people is this? Is this a class I or a class to rebroadcast?
Well, the wait is further away from the fulcrum than the force, counteracting the weight. So the load is much further away than the force that's contracting it. So therefore this must be a class III lever. OK what you then do is resolve your moment times, this will find out where your arms are. So in this case, the moment armed for here is perpendicular to the force of the abduction, everyone happy with that.
And the momentum for your weight of your arm. Is perpendicular to the direction of the weight of the gravity disappears. The weight of your arm so perpendicular to the direction of the force, which is gravity straight down. OK, so if we call this d, I take this line D as an added to the momentum of w. What we say is that probably around four d, let's say, or 5D.
Let's say if I die for the sake of argument, OK, so force. Course by the. Is equal to. By dw. So F is equal to 5 times the way to the r. Because I hope you all understand that, as you can see that it's not that difficult, you just need to work your clockwise and your anti-clockwise direction.
OK the then what you need to do is correct your vectors and get your joint reaction force. So That's f we are W2 D f, which is in this direction. No tip of the arrow tail of w goes to the tip of the arrow of f. And then you connect the two.
There you go. So that's our joint reaction force, this is the direction our joint reaction force goes. And we can make a guesstimate that since F is equal to 5 w, this is now losing a part of a. We can say this is 4 and 1/2. W is the joint reaction force.
And if you move that there, this is the direction of your joint reaction force. OK if you think about it, if is trying to shove the show, the humerus into the glenoid. And if this is an equilibrium, there must be an equal and opposite reaction from the glenoid and that is your joint reaction force. OK, that's brilliant.
Juan, thank you very much. That's really excellent. We have a few requests about the need. There is just one very pertinent question about this stuff and ask, why am I taking 4 and a half? OK, so I'm just this is a gross estimation. This is not saying that this is mathematically accurate in any way whatsoever, but it's a gross. So what I'm doing is if I take this line here and just bring it back to there, if you imagine I'm pivoting that line, the line back onto the line, what you're advancing is not all of the W is taken there.
Do you see that if I take this w, that's where it should end up there? So therefore, I'm saying it's about half of w. So the graph is 4 and 1/2 times w. I hope that it answers your questions to us. So sorry for us, where were you? So I think that's excellent explanation, as you said these numbers, you could use this part of your assumptions here.
And as long as you can justify this, you could put any numbers you want. We just had a few questions, Sean, about the knee joint. And people need to be clear that the knee joint that we took, which joint we are talking about, is it the actual knee joint or patella from a joint? And I think people want to know about the formal joint. It's very difficult joint this one and a lot of controversies around it and I don't know, applies to things for us.
So thank you for us. I never started the formal joint by talking about the. Because you can't resolve for a federal family joint unless, you know, the forces around the joint, which you which means you have to go much further than what we are describing here, ok? So it's always a trick question, and they say resolve showed me a free body diagram for the telephone once everyone starts doing that.
What then happens is that they get themselves stuck because then people don't know what the number is for those forces. So the way to start that is to actually just talk about the joint reaction force around the new. OK, so what we do is if I draw the ground. Here when I draw this, a person is in a crouching position just about to sit down.
This is his tibia. And this is his femur. OK, so then what I then say is that this person's weight is going through just around the knee, just change the color so you don't get mixed up with the colors. This person's weight is just about here. OK because remember, if they're crouching, they're leaning forward, so they're halfway over their FEMA.
This person is now in equilibrium. Who's crouching like this? OK so right now in this crouched position, this is w. So what is trying to keep the person straight up, it's not his hamstrings, it's not his Achilles tendon, it's not his band. It is a quadriceps. So his quadriceps are now in action.
If you take a look at this, if this is the folk and let me just draw a little oval so you can see where I'm putting the fulcrum just there. If this is the fulcrum, w wants to go anti-clockwise and the quadriceps are attached to the pelvis, and they were presuming they are just talking about the full muscle of the pelvis or the top of the femur. The what we are saying is that the sorry just been to get a line.
What we're saying is this is the force of the quadriceps. OK that's the anti-clockwise force. So what type of leader is this is the fulcrum is here. The weight is closer to the fulcrum, but the force is further away or the load is closer to the fulcrum. The force is further away.
It's like a real battle. It's a class Ii lever. OK, so now you've created yourself a simple task to lever. We call this f. So now we need to resolve for this, so if we switch again to our blue to get our arms. But that's our first moment.
And this is our second moment on. You give me a few, if I'm drawing very small here in the exam, as I said, draw very big. So if this is the then this, let's say, is 40. OK, so f is our clockwise action F multiplied by d? Is equal to w, which is our anticlockwise action multiplied by 4.
The Divide, take away our odds F is equal to 4 times. The body weight. So that's our. That force is equal to 4 times. Now we want to do joint reaction force on this, so if we take the joint reaction force here, what we then do is let me just switch colors because this is getting more complicated. So I just want to make sure we're in the same light colors.
If we take. If everyone agree that that's just about the same line, and then we add w. Sorry our joint reaction force is. Well, this direction. OK, so.
W now. And joint reaction force there, ok? No, if that's the joint reaction force we then have. Is equal to 4 and 1/2 times. Bodyweight, now what we then do with that is we switch, we switch to the kneecap. And if we draw the kneecap as oval.
To represent the firm epicondyle, I apologize, let me change color again to red so that we can see what we're doing. This is quite complicated, so that's why I'm taking a little time to make sure you all understand this. So that's your condyle. And what I'll do is I'll draw the kneecap free hand.
You don't like this. OK, so now we know that there's a force of quadriceps, which is equal to 4 acting on this person. Correct the keeping the person alive, but there must be an equal and opposite reaction of 4w. Struck again.
In the same in the opposite direction of a. OK, so we call this African. The if this is in balance, there must be a straight if this is an equilibrium, they must be an equal and opposite reaction to air, which is the patellar tendon, which is going straight down again. It must be an equal magnitude to a.
OK, you call it patellar tendon for now, but it's equal to equal to f in magnitude because it's in balance. Now if you want to resolve the joint reaction force, here is we have that remember, I showed you that principle of the game. So if I draw that as a parallelogram? And there's your joint reaction force, which you can appreciate it's smaller than at, so therefore let's key in the path.
Finds the body weight, which is quite a significant amount to put through your kneecap. Hope that makes sense. I think that's excellent. One really is very complex joint and you explain that very well. I think this joint is possibly the most difficult. Joint for them already. So I think that's very useful and people can.
Definitely listen to this recording later on to review. I think we are getting worse was the end. One more, if you don't mind for us, this is what we have. We have another two or three minutes one. So just very quickly the finger, everyone, the elbow and the finger, they're both the same, by the way. OK, I'll just draw them both parallel to you so you don't waste time.
OK, so the. If I say, first of all, let's draw the elbow one person. If this is my. US this is my honor. Let's draw the finger. The thing is, everyone tries to draw the finger like this and put a weight like that on it, but nobody walks with the weight on their finger like that.
If you can use shopping bags, you carry it like this. Isn't that right? OK, so why don't you draw your finger like that? Which is then now this is your phalanx. This is your proximal phalanx. This is your middle phalanx in your letter, your small Thanks again. If were this is now this is now what I would call a class III lever, an efficient lever, the most inefficient in the body.
OK what we then do is withdraw our forces for that, we have the biceps here. And in this case, we have the fifth. Yeah we have to wait here. And here we have the weight of not just the thing, but the bag they're carrying. You can say the person is carrying in a weight in the hand as well, so that's W for hands.
That's next for hiring NSW for the way to the arm. And you can say this person is carrying a bag which the way to the arm is negligible, the weight of the phalanx is negligible, so we can call this w ulnar claw. OK, so if this is f and this is f, you can appreciate that all you need to do is resolve your clockwise and anticlockwise forces.
The F is equal in this case. Let's talk for this one. So if we call this d, which colors again, so basically. This this perpendicular distance, and if this is then 5 and this is another body on top of that, we can then say if. He is equal to 60.
W plus. For the act. If you want to make life much easier for your elbow because this is what they say, a patient is carrying a weight on the hand, then just neglect. Get rid of this W and just say this is the weight of the whatever they're carrying and the weight of the arm all together in one, and that makes your life much easier.
But anyway, there you are. This is equal to 6 W I'm the same here. This is the year before this claw palsy. Is equal to w or dD's and equal to 4 w. OK, that's brilliant. Three levers in the body, and you can create the same levers in any joint.
Just excellent. Thank you very much. And we have to wrap up this session because it's about to. Our time is about to finish here next. Next session will be hot seat by the session. Priority will be given to the February candidates. Not everyone would have a chance to have a go, but some people can just watch and learn. Some people can have a go, as one would be asking some of the common questions and giving some feedback just to give you a little bit of practice.
So I will end the session everyone and I will send you another link for the Viva session. If you have any burning questions you want to ask, you also will let you ask during the session. Thank you everyone who has joined so far and I will post another link shortly. Thank you.
Segment:0 .
OK, everyone. Thank you, everyone, to everyone who has come back. Thanks, Juan. Give us give us very good introduction to the principles behind free diagrams and hip and ankle diagrams drawings. He's going to continue now with next half an hour with more.
More joints. And please, please keep your comments and questions coming. I just have to let you know. After this session, we will carry on a small Viva session for people who want to be take a hot seat on. Or people who just want to watch. But that would be after this next block over. Guys who are going to sit there for three repeating this for some of you guys.
So it's worth giving you something else as well. OK thank you, Ferre. Over to you. OK thank you for us. The so we discussed hips, we discussed ankle, I showed you how you can chair the class one levers are easiest ones to resolve. And I showed you how you can change an Ankle to cast one lever as well.
There's another class one lever in the body. There's actually two more class one levers that you should pretty well. Ok? the first one is the spine purposely going to difficult ones. Everyone tends to think that these difficult ones are really hard. They're not.
They're very straightforward, very easy. Nothing to worry about. So for the spine, what I would do is I would draw to declare two motion segments of the spine. Essentially, this is two vertebrae. And the way I would describe this to the examiner, apart from talking about all my assumptions which we discussed earlier on, I would say this person is leaning forward.
OK so I appreciate that this drawing is like leaning forward, but it's just easier to draw it this way using this whiteboard. So imagine this person is leaning forward and the person is leaning forward. Then what we have is the person's whole weight, and he's carrying the weight as well. Let's presume he's carrying the box with arms straight and leaning forward, so he's hanging down.
So the whole weight of the body and the weight of the box all combined gives you a force of w. Just W just there. OK OK, so what's counteracting this force? Remember, our center of gravity is our center rotation is the disk.
And are interesting and quite badly. As I said, I'm not used to this. There this. OK, so our center is the middle of that desk, so what's the forces that are going there are the spinal muscles, ok? They are then creating a. Forced in the opposite direction.
And then we're assuming this patient is meaning. OK so this force is. So then we just do the same thing that we get, everyone else is type I cast one lever, so there's nothing special about it. We just change the color to you. You can see the moments on.
And I suspect all of you have already kind of worked out how to draw this. If you raise this up to date and then this one is perpendicular again. And remember, this is a mathematical symbol for perpendicular. OK, so even if you're not going perpendicular, if you draw that and say it's perpendicular, the examiners have to accept it because you were saying momentum is perpendicular to the direction of.
OK, so if we say this is D. The shortest one is the and then just take that as a multiple of these in this case, a the reality is in real life, you're drawing something like five or 60, but it's very hard to draw this on a small piece of paper then resolving our forces we've got. By D equals, we BW cancel out Kessler suture degrees F is equal 3 times weight.
In this case, weight includes the weight of what the person is carrying. OK, so what's our joint reaction force? So again, it's the same thing. It's a type I either. All you need to do is just add these legs together. And then do an equally opposite reaction force. OK, so once again. I would agree that is where it should be parallel.
And then just add another line down there, and then of course, these are the arrows. So this is w And this is. And then you go from tip of arrow, you add the tail to the tip of the arrow to the tail of the last, the first arrow.
And that's our joint reaction force. OK again, if you say this is 3-d, this is w if we w apologize w tenodesis w, you can presume that you can take a guesswork with jerk reaction force equal to 3 and 1/2 times right now. Please be aware. You should draw this really big exam and don't use 3D as your. No, it should be something around the line or five or 60 because the weight your body weight is actually very far away from the center of rotation.
You're leaning forward compared to your spinal muscles, the muscles that are erect and so on. OK does that make sense? So do your line. But I'm just showing you. It's just a simple class form again. OK the next one with some examiners asked about the weight of the head on the cervical spine and how it affects the T2 C2.
OK, so once again, just simple diagram, nothing fancy. Don't be a hero. Don't do anything foolish. Just do a simple diagram. So circle for a head. OK, I'd like to draw my circle like an egg to represent the skull.
The simple rectangle for your. The spine. And say your center of gravity, so your center of rotation, your function is just there, ok? That's that's it. That's all it is. OK, so once you've done that, you can then take your weight again.
OK and then again, the muscles at the back of your neck. OK and once again, it's a type class one labor type, class one labor.
There's your. Two different forces, if that's D And that's d, then fd equals dw. Therefore, F is equal to the weight of the stock. Simple as that. Of course, again, you could make a 2 day as in the wake of your patient is leaning forward, so therefore the weight is far more forward.
So you make it to can say that in the exam if you wish to say that. OK, so and then now to calculate your joint reaction force here, then it's just add the F vector F. To vector W OK in this case, because we've decided the FMW are the same size, let's just redraw that as FMW. Then you don't reaction force is equal to. To w.
Does that makes sense, I hope everyone understands this. Look again, if you do decide that you are leaning the head forward and I would advise you to do that, make your W far more forward and say it's too D as opposed to distances 2 times D OK, so therefore you can then get F is equal to 2 w, then your joint reaction force will be f-ing.
Joint reaction force will be equal to 3w. OK you are. I'm sorry, I just want to make sure you'll understand when you're drunk, when you're drawing pictures, when you're adding vectors, you add them in the way you would add a parallelogram. But what we're doing is we're taking a little cheat instead of doing parallel.
We're doing a triangle and just to show you what I mean. If I take a line. And just like that. Take another line like that, and I want to resolve the forces on this point here. These are two forces. If I want to resolve these two forces on this point here, I then draw a parallel line like this. There, which is the equivalent of x, and this is why I draw another line parallel, which is why.
OK does that make sense? This is something for want of a better way of saying it and why can't? What we then have is. The sum of these two vectors is in this direction. These two forces are working in this way. And you can appreciate. It's quite a large vector. Magnitude is increased, as you can see.
And also the force direction is increased. So what we're really doing here is we're just not including this part. All we're doing is a triangle. So we're adding this force and then we're taking the next triangle and taking it. Sorry, I didn't make myself myself. So we're taking this course. Adding another force this way, because we want to talk about opposite and equal reaction that sum of these two forces must give you an opposite reaction in this direction.
Does that make sense? OK, so you all understand how to add vectors in this way? OK OK. Sean, what are you talking about this? I had a good question coming through just a bit more expansion on the hip free body diagram and a little bit more explanation from you on how they're using a stick affects the joint reaction forces.
How is the difference between using stick on one hand on the, you know, the affected side versus using it on the contralateral side? And how does this affect joint reaction forces? If you could briefly touch on that, let me just quickly draw the hip again. OK so. If if this is the person's weight.
W and we have abductors going here. Yeah if the patient is carrying a stick on the opposite side. That's the force of the stick. Yes OK, so then what happens here is if you take the moment of those two forces, if you think about it, this is a seesaw. So if I draw you a seesaw? There you are.
This is a seesaw. This is the abductor force doing this to this, and this is the weight of the person doing that. And this is the stick doing that. As you can see, the two forces that are working together is. And yes, they're on the same side, they're trying to rotate the seesaw anticlockwise. The only thing that's working clockwise is w.
OK, so this is what we're essentially resolving here, we resolving those forces. So if you imagine if you take f as your force abductor and you add s to it. You don't need a lot of f, you don't need a lot of adapter for us to counteract the effect of your body weight because you have as helping you. Isn't that right? But if you have no S if.
This is absent, then, yes, you do need quite a large. You do need quite a large and I do appreciate that I've drawn the distance is wrong, but I just wanted to show you the principle of a seesaw here. That's what we call a type I lever. So if you type 1 lever is in balance, then all forces must be resolved in equal within. And if you put your stick on the opposite side, so if you have a stick here on this side.
Instead, OK, let's call this again, I appreciate I'm not going to back those on the right side, but I just want to be able to see them. So let's put that S on this C So here. And then you can see that as here wants to help the weight. So what's happening is she wants to change the direction to clockwise, it wants to flip the seesaw clockwise and the only m.w., so they're working together, while f is the only force that's working anti-clockwise.
So this is all in balance, then F is equal to w plus s. OK, because the reality is f-minus asked initially, and then you take over the house to the other side and F is equal to. Does that make sense? OK, so you can appreciate the F here who is working far more hard or your abductors are working far more harder.
And if your abductors are working far more harder, then far larger magnitude of a vector. And if it's a far larger magnitude of a vector, you have to add a W on to that. And of course, you've minus the bit of s away, and now you've got a far larger joint reaction force. I hope that explains it, why you need to stick it on the side. This one that explains it very well, thank you.
I had another question. Schwann different type of lever is the shoulder joint and people want to hear from you. How would you draw a shoulder free body diagram? OK, so these are the other levers that we need to move on to. That's correct. OK, so let's talk about the shoulder. All right.
So we'll start with that one. Once again, let's remember we're not doing anatomy, and you must talk about your assumptions when you're drawing. OK, so the best thing to do with this is everyone thinks that they need to draw the shoulder down. The problem with that is then you've got more complex muscles active in that situation, then you really need and you're now finding it very hard to find out where the direction of your biggest muscle your deltoid is going because you can appreciate your deltoid just now working as a 90 degree angle muscle as opposed to if you put it up here, it's not working as a contraction muscle.
Does that make sense? So the best thing to do is draw your shoulder perpendicular to parallel to the ground or just close to parallel to the ground. So if we take a. The small oval to show the humeral head to a line. Before the humerus or the arm. And draw the circle to represent the glenoid. No, that's all you need to draw for all of this.
You just say that the ground the arm is held out, it's almost parallel to the ground. Then you put the weight of the whole arm through the center of the arm in this case will put it very close to the edge so that you can see the difference. That's w. And then what you then now need to worry about is your deltoid, so your deltoid is a large force.
In this direction. OK does that make sense? Can everyone appreciate that the deltoid is now working in that direction if you go through the cross section of the muscle? So now what we need to do is. So what type of people is this? Is this a class I or a class to rebroadcast?
Well, the wait is further away from the fulcrum than the force, counteracting the weight. So the load is much further away than the force that's contracting it. So therefore this must be a class III lever. OK what you then do is resolve your moment times, this will find out where your arms are. So in this case, the moment armed for here is perpendicular to the force of the abduction, everyone happy with that.
And the momentum for your weight of your arm. Is perpendicular to the direction of the weight of the gravity disappears. The weight of your arm so perpendicular to the direction of the force, which is gravity straight down. OK, so if we call this d, I take this line D as an added to the momentum of w. What we say is that probably around four d, let's say, or 5D.
Let's say if I die for the sake of argument, OK, so force. Course by the. Is equal to. By dw. So F is equal to 5 times the way to the r. Because I hope you all understand that, as you can see that it's not that difficult, you just need to work your clockwise and your anti-clockwise direction.
OK the then what you need to do is correct your vectors and get your joint reaction force. So That's f we are W2 D f, which is in this direction. No tip of the arrow tail of w goes to the tip of the arrow of f. And then you connect the two.
There you go. So that's our joint reaction force, this is the direction our joint reaction force goes. And we can make a guesstimate that since F is equal to 5 w, this is now losing a part of a. We can say this is 4 and 1/2. W is the joint reaction force.
And if you move that there, this is the direction of your joint reaction force. OK if you think about it, if is trying to shove the show, the humerus into the glenoid. And if this is an equilibrium, there must be an equal and opposite reaction from the glenoid and that is your joint reaction force. OK, that's brilliant.
Juan, thank you very much. That's really excellent. We have a few requests about the need. There is just one very pertinent question about this stuff and ask, why am I taking 4 and a half? OK, so I'm just this is a gross estimation. This is not saying that this is mathematically accurate in any way whatsoever, but it's a gross. So what I'm doing is if I take this line here and just bring it back to there, if you imagine I'm pivoting that line, the line back onto the line, what you're advancing is not all of the W is taken there.
Do you see that if I take this w, that's where it should end up there? So therefore, I'm saying it's about half of w. So the graph is 4 and 1/2 times w. I hope that it answers your questions to us. So sorry for us, where were you? So I think that's excellent explanation, as you said these numbers, you could use this part of your assumptions here.
And as long as you can justify this, you could put any numbers you want. We just had a few questions, Sean, about the knee joint. And people need to be clear that the knee joint that we took, which joint we are talking about, is it the actual knee joint or patella from a joint? And I think people want to know about the formal joint. It's very difficult joint this one and a lot of controversies around it and I don't know, applies to things for us.
So thank you for us. I never started the formal joint by talking about the. Because you can't resolve for a federal family joint unless, you know, the forces around the joint, which you which means you have to go much further than what we are describing here, ok? So it's always a trick question, and they say resolve showed me a free body diagram for the telephone once everyone starts doing that.
What then happens is that they get themselves stuck because then people don't know what the number is for those forces. So the way to start that is to actually just talk about the joint reaction force around the new. OK, so what we do is if I draw the ground. Here when I draw this, a person is in a crouching position just about to sit down.
This is his tibia. And this is his femur. OK, so then what I then say is that this person's weight is going through just around the knee, just change the color so you don't get mixed up with the colors. This person's weight is just about here. OK because remember, if they're crouching, they're leaning forward, so they're halfway over their FEMA.
This person is now in equilibrium. Who's crouching like this? OK so right now in this crouched position, this is w. So what is trying to keep the person straight up, it's not his hamstrings, it's not his Achilles tendon, it's not his band. It is a quadriceps. So his quadriceps are now in action.
If you take a look at this, if this is the folk and let me just draw a little oval so you can see where I'm putting the fulcrum just there. If this is the fulcrum, w wants to go anti-clockwise and the quadriceps are attached to the pelvis, and they were presuming they are just talking about the full muscle of the pelvis or the top of the femur. The what we are saying is that the sorry just been to get a line.
What we're saying is this is the force of the quadriceps. OK that's the anti-clockwise force. So what type of leader is this is the fulcrum is here. The weight is closer to the fulcrum, but the force is further away or the load is closer to the fulcrum. The force is further away.
It's like a real battle. It's a class Ii lever. OK, so now you've created yourself a simple task to lever. We call this f. So now we need to resolve for this, so if we switch again to our blue to get our arms. But that's our first moment.
And this is our second moment on. You give me a few, if I'm drawing very small here in the exam, as I said, draw very big. So if this is the then this, let's say, is 40. OK, so f is our clockwise action F multiplied by d? Is equal to w, which is our anticlockwise action multiplied by 4.
The Divide, take away our odds F is equal to 4 times. The body weight. So that's our. That force is equal to 4 times. Now we want to do joint reaction force on this, so if we take the joint reaction force here, what we then do is let me just switch colors because this is getting more complicated. So I just want to make sure we're in the same light colors.
If we take. If everyone agree that that's just about the same line, and then we add w. Sorry our joint reaction force is. Well, this direction. OK, so.
W now. And joint reaction force there, ok? No, if that's the joint reaction force we then have. Is equal to 4 and 1/2 times. Bodyweight, now what we then do with that is we switch, we switch to the kneecap. And if we draw the kneecap as oval.
To represent the firm epicondyle, I apologize, let me change color again to red so that we can see what we're doing. This is quite complicated, so that's why I'm taking a little time to make sure you all understand this. So that's your condyle. And what I'll do is I'll draw the kneecap free hand.
You don't like this. OK, so now we know that there's a force of quadriceps, which is equal to 4 acting on this person. Correct the keeping the person alive, but there must be an equal and opposite reaction of 4w. Struck again.
In the same in the opposite direction of a. OK, so we call this African. The if this is in balance, there must be a straight if this is an equilibrium, they must be an equal and opposite reaction to air, which is the patellar tendon, which is going straight down again. It must be an equal magnitude to a.
OK, you call it patellar tendon for now, but it's equal to equal to f in magnitude because it's in balance. Now if you want to resolve the joint reaction force, here is we have that remember, I showed you that principle of the game. So if I draw that as a parallelogram? And there's your joint reaction force, which you can appreciate it's smaller than at, so therefore let's key in the path.
Finds the body weight, which is quite a significant amount to put through your kneecap. Hope that makes sense. I think that's excellent. One really is very complex joint and you explain that very well. I think this joint is possibly the most difficult. Joint for them already. So I think that's very useful and people can.
Definitely listen to this recording later on to review. I think we are getting worse was the end. One more, if you don't mind for us, this is what we have. We have another two or three minutes one. So just very quickly the finger, everyone, the elbow and the finger, they're both the same, by the way. OK, I'll just draw them both parallel to you so you don't waste time.
OK, so the. If I say, first of all, let's draw the elbow one person. If this is my. US this is my honor. Let's draw the finger. The thing is, everyone tries to draw the finger like this and put a weight like that on it, but nobody walks with the weight on their finger like that.
If you can use shopping bags, you carry it like this. Isn't that right? OK, so why don't you draw your finger like that? Which is then now this is your phalanx. This is your proximal phalanx. This is your middle phalanx in your letter, your small Thanks again. If were this is now this is now what I would call a class III lever, an efficient lever, the most inefficient in the body.
OK what we then do is withdraw our forces for that, we have the biceps here. And in this case, we have the fifth. Yeah we have to wait here. And here we have the weight of not just the thing, but the bag they're carrying. You can say the person is carrying in a weight in the hand as well, so that's W for hands.
That's next for hiring NSW for the way to the arm. And you can say this person is carrying a bag which the way to the arm is negligible, the weight of the phalanx is negligible, so we can call this w ulnar claw. OK, so if this is f and this is f, you can appreciate that all you need to do is resolve your clockwise and anticlockwise forces.
The F is equal in this case. Let's talk for this one. So if we call this d, which colors again, so basically. This this perpendicular distance, and if this is then 5 and this is another body on top of that, we can then say if. He is equal to 60.
W plus. For the act. If you want to make life much easier for your elbow because this is what they say, a patient is carrying a weight on the hand, then just neglect. Get rid of this W and just say this is the weight of the whatever they're carrying and the weight of the arm all together in one, and that makes your life much easier.
But anyway, there you are. This is equal to 6 W I'm the same here. This is the year before this claw palsy. Is equal to w or dD's and equal to 4 w. OK, that's brilliant. Three levers in the body, and you can create the same levers in any joint.
Just excellent. Thank you very much. And we have to wrap up this session because it's about to. Our time is about to finish here next. Next session will be hot seat by the session. Priority will be given to the February candidates. Not everyone would have a chance to have a go, but some people can just watch and learn. Some people can have a go, as one would be asking some of the common questions and giving some feedback just to give you a little bit of practice.
So I will end the session everyone and I will send you another link for the Viva session. If you have any burning questions you want to ask, you also will let you ask during the session. Thank you everyone who has joined so far and I will post another link shortly. Thank you.
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