Knee Joint Biomechanics Overview

Welcome back in today's video we are going to discuss about one of the most important aspects in knee complex that is the knee complex biomechanics or the knee joint kinematics the movements possible around the knee complex we often think that the possible motion is only flexion and extension but there is flexion extension medial rotation lateral rotation abduction and adduction addiction that means three degrees of freedom and six possible motion along with three translatory motions. We are going to discuss each one of them in particular. In today's video, we will be focusing on the principal motion around the knee complex that is flexion and extension. Along with that the role of anterior and posterior cruciate ligament in flexion and extension, the role of menisci in flexion and extension, and finally the pathomechanic in flexion and extension movement. If you wish to know any one in particular, the time codes are given below in the description and comment box, you can check on to that. Here we discuss the knee complex biomechanics, in particular the joint flexion and extension. Ticks in the knee joint that means the movements possible in the tibiofemoral joint we are focusing on the tibiofemoral patellofemoral we will discuss later in tibiofemoral joint we have three degrees of motions i told you earlier that is a flexion extension which are the principal motion or predominant motion abduction adduction of course varus and valgus and finally media rotation or lateral rotation or internal or external rotation. When we evaluate the knee complex or any joint we need to have a joint axis for the motion to take place. But in human body we often discover that the axis is not a fixed one like a mechanical joint but it is an instantaneous one. Especially because the condyle or the surface articulating surface are not concurrent to each other. That means in every degree of knee motion and every particular motion the axis is not fixed but an instantaneous axis of motion. The points of the axis constantly changes. And that makes the knee joint movements much more complex. Along with the three degrees of rotatory movements, we have three translatory motions that is the anterior and posterior gliding or translation, the medial and lateral translation and of course a pure spin and anterior displacement movements in the Nikon. We will discuss each one of them in particular but first we will focus on the flexion and extension and all the arthrokinematics, arthrokinematics means glide, slide, spin etc. as well as the osteokinematic movement, the flexion extension in particular and how this comes together to make a beautiful and a systematic movements possible in the knee complex. before that let us look into the instantaneous axis of rotation of the knee complex. You can see here the instantaneous axis of femoral motion. I described it earlier that is the axis is constantly shifting. You can visualize different color schemes for the different levels of femoral motion, different degrees of femoral motion. And according to that the axis is shown or it is constantly changing or we have an instantaneous axis of femoral motion for each degree of knee flexion and also for knee extension. Yes. and now we move on to the principal motion in the knee complex that is the flexion and extension flexion and extension the flexion and extension is the principal motion in the knee complex and for identify the motion we need to identify the axis the axis is an axis passing through both the femoral condyles both the femoral condyle It's a horizontal line passing through both the femoral condyles and we call that axis trans epicondylar axis. the movement in the knee complex that is a flexion and extension takes place in a trans epicondylar axis which is nothing but a straight line passing through the femoral condyle it's the lower end of the femoral condyles right and but as I told you the axis is instantaneous so this axis is not Fixed one it changes constantly during the knee motion But need not complicate that you just remember in your mind in knee joint motions The trans epicondylar axis is not a fixed one It is constantly moving just that you need to get into mind now. Let us look into the motion Looking into the motion. We first need to remember it is a trans epicondylar axis passing through the femoral condyles epicondyles epicondyles right you just have to remember this in mind let it be in our mind now the first motion possible is flexion and then the extension let us evaluate this what is actually happening during flexion and extension you see that the femoral condyles are what you call convex and they are larger than the tibial condyles now for flexion to take place let us imagine a situation where the to tibia is fixed that means your tibia cannot move and femur is moving on the tibia there is an alternative like femur is fixed and tibia is moving but here we are going to take a consideration where fitibia is fixed and femur is moving can you give a real life experience a real life example for that that's our weight bearing position any of the weight bearing position team tibia is fixed and we can say that femur is moving that is for example in weight bearing you go for a squatting okay the tbi is fixed down there relatively fixed and the femur is moving okay so in that situation for example in squatting what happens is that for femur to move into the flexion okay for the hip to move into flexion or femur to move into flexion at the knee joint the femur should go backwards this is the flexion okay this is flexion here the tibia is flexed fixed and this is the flexion at the hip and knee right so this is the flexion and during this flexion The osteokinematic movement is flexion itself. Okay and what is the arthrokinematic movement? Femur roll downwards or rolls posteriorly. Right you can imagine this is what happening. This movement is known as the rolling of femur posteriorly. Femur can roll anteriorly but if femur moves anteriorly, flexion won't happen. So femur should move posteriorly. Right that's the first point to guess to remember. And now what is happening Imagine this is a let us get into this let us imagine this is the tibia and you have the femur just look at this clause look at this picture in clause you imagine that the femur is only moving going for a rolling okay femur rolls on the tibial condyle you just see that after the rolling happens rolling happens rolling happens rolling happens and at one stage you see the femur will not be in a position of contact with the TBR condyle. or the surface area on the tibial condyle gets finished that means femur cannot go in contact it should go like this okay can you guess it let us once again see that so imagine look at the lower end of the femur imagine what's the motion that is a rolling the flexion during flexion the femur you imagine a situation where femur is just rolling this is the rolling okay Just rolling like this rolling rolling rolling over rolling over rolling over rolling over and some degree of knee flexion you can see that Absolutely very little contact is only between femoral condyle and the tibial condyle and at this particular position Femur will be in a disadvantage. That is a disadvantage to the femur, right now How is it over come? This is overcome like this when femur is going to roll like this is okay After a few degrees of rolling, just look at this, after a few degrees of rolling posterior, this is the posterior rolling, what is going to happen? The femur is going to translate anteriorly. That means slide or glide anteriorly along with rolling. So that at every point, there is actually enough contact between the femoral condyle and the tibia. Should I explain it once again? Let us see it. So this motion is a disadvantageous one if there is roll alone. So in order to prevent that, in the fixed femur tibial content, the femur along with its rolling, the femur is going for an anterior translation. That means femur will go for an anterior glide. And this anterior glide when it is accompanied by the posterior roll, there is a perfection so that femur can go to the highest possible flexion how many how much degree is possible it can go up to that much otherwise it would be limited let us see that again once again I believe you can see it right you see this is the rolling this is the rolling and during this rolling after a 25 degree of rolling that's how it is so 0 to 25 degree of flexion there is pure rolling itself okay only this motion only this motion after 25 degree of rotation just you can see that please look at the lateral condyle what is happening the femur motion will be accompanied by the sliding motion so that at all ways anterior slide will be induced so that at all ways there is a contact between the tibial condyle and the femoral condyle right the tibial condyle is a concave one this is convex one this is what happening in the convex concave rule that is when a convex is moving on a concave the arthrochiaromatics and osteochiromatics occur in the opposite direction here when the flexion is occurring and posteriorly in the posterior roll is occurring what is happening there is an anterior translation the glide is anteriorly in the anterior direction so that is how the motion of femur is being initiated in the knee complex that is in the tibio femoral joint so initially from 0 to 25 degree there is only translation only rolling 0 to 25 degree there is pure rolling alone and greater than 25 degree roll is accompanied roll is posterior posterior roll is accompanied by slide or glide it can be same okay slide or glide anteriorly see that's how the knee flexion is going to takes place let us examine that with the help of a diagram this is a scenario where we discussed about the squatting position that is femur is moving on a fixed tbm and you can see that friction which is shown by the red sign is actually rolling which is happening in the posterior direction whereas slide is shown it is alternating on as glide is shown in the anterior direction so this is what actually happening anterior slide as well as a posterior rolling or during squatting position whereas when we look at the squat to up that is getting up that is extension the anterior rolling is accompanied by posterior slide. So this diagram clearly illustrate the difference between anterior and next extension and flexion flexion is accompanied by posterior roll posterior glide and posterior roll and anterior glide whereas extension is accompanied by what you call the anterior roll and posterior slide or glide that's one scenario the squatting scenario is going for flexion okay now we are going for extension that is from squatting position you are getting up that is an extension which is opposite of flexion right yes what is happening the things are same but the femur is in flexed position and tibia is fixed for this consideration that is the person is in squatting he need to get up he is going to get up here a roll is coming anteriorly right the femur is going to roll anteriorly similar to earlier condition when there is a pure rolling there can be a problem like the tibial condyle's articulation is going to finish off and to prevent that what is happening the same mechanism Here there is a rolling. Here there is a rolling in initial degree. But after that, along with the anterior rolling, the posterior sliding takes place. And this initiates a complete flexion. So along with rolling posteriorly, rolling anteriorly, here slide, here slide is going to happen posteriorly. So rolling anteriorly, sliding posteriorly. So that always this contact. tails are in articulation so that is what happening in extension initially that is followed by a rolling and then it is followed by what you call a posterior anterior roll is accompanied by a posterior translation or posterior slide or glide that is how the motion of extension and the motion of flexion is taking place in the knee joint and now you see that after 25 degree there is a roll plus slide okay there is roll plus slide. So you can call it as a pure spin movement. That means after 0 to 25 degree or after initial degree of flexion and extension, the motion that is taking place in the femur is a pure spin motion. Spin can be called as a movement around an axis. This movement along with that in literature a movement combining pure amounts of same The same amount of rolling and gliding is also known as a spin moment. So we call this as a pure spin moment. But if that is confusing just leave that and just check on to this. So during the position of weight bearing or during some examples like a squatting, when femur is fixed, sorry when tibia is fixed, the femoral motion of rolling takes place in one direction and the glide motion that is taking place inside the joint occur in the opposite direction. that is if flexion is occurring if flexion is occurring the gliding is occurring anteriorly if extension is occurring the gliding is occurring posteriorly all right i hope that is clear now let us move on to the second scenario where your femur is fixed your femur is fixed right here the scenario is different that is our femur is fixed yes what is a real life example For example, you are sitting in a table and you are extending your knee. Or the quartz table is an example of this one. You are extending your knee, your femur is fixed and the only possible motion possible is the femoral, the tibial motion, tibial flexion and extension. Let us look back into this one. See this scenario Here the entire thing changes only the femur is, tibia is moving and femur is fixed. So you can fix it this one and there is no possible absolute movement possible. So during knee flexion that is during knee flexion that is the tibia should go for flexion. The tibia should go for flexion okay. Now you imagine this is a concave on convex okay. This is a concave this gravity is concave on convex. What should happen when there is an argyrokinematic and osteokinematic should occur in the same direction remember that. Now let us imagine, see when tibia is going for X flexion, what is happening? Let us imagine what is happening. For example in flexion of the knee at this position that is the tibia is moving. When tibia is moving for flexion what is happening? There is the posterior roll, right? The rolling is of the posterior direction and along with you can just imagine look at this clearly along with that posterior roll. Along with that posterior roll, the slide is also posteriorly. Right? Along with that posterior roll, let us fix it like this, along with that posterior roll, the slide is also posteriorly. So that will help the motion to take place. But for example, you imagine this is going posterior roll, but if this is going for anterior slide, okay? Like the femur. For example, this is going for posterior roll. and this is going for anterior slide if it is sliding anteriorly you can see that this joint will slip off or there is no concurrency or articulation between this one so in order to prevent that during this posterior rolling during this posterior rolling from this position the slide is also taking place posteriorly for example the slide is also going to the slide is also going to take place posteriorly see see this one slide and rod is posteriorly right the slide and rod is posterior the slide and draw is posteriorly you can see that right it is not uh rod posteriorly and anterior slide it is slide and rod in same direction that is explained by the convex concave surface moving on a concave one and along with that during flexion to extension this is the flexed position of the knee uh sorry always femur is moving femur is flexed and femur is fixed and knee is flexed okay now in this position the femur the tibia moves anteriorly along with that anterior translation or anterior slide okay just imagine this one see this how beautiful it is uh you see this is the situation and this is already a flexed knee and from this flexed knee um this should move for extension when it is moving for this roll see this one is the roll along with that this slide and teacher slide of course so when femur is moving on the fixed tibia the rolling and sliding is in opposite direction but when tibia is moving on a femur this both are in same direction that is from a tabletop knee extension when tibia is extending moving anteriorly when tibia is moving anteriorly that translatory movement that is a glide also occur anterior during a tabletop knee flexion when tibia is moving posteriorly when tibia is moving posteriorly the glide also occur posteriorly right all these are done to ensure that always there is a complete accuracy or concurrency between both of the joints. Let us see this with the help of few diagrams. You can see here that example described earlier the extension is followed by or accelerated by anterior translation that is in extension the anterior translation happens whereas in flexion you can see that flexion is accompanied by posterior translation. So in cases like a femur is fixed the arthrokinematics and osteokinematics takes place in same direction. And now we move on to describe the role of ACL and PCL in knee flexion and extension. Let us move on to describe the role. Yes, the role of cruciate ligament in flexion and extension. You know that we have anterior cruciate ligament and posterior cruciate ligament. And each of them are having a separate role in knee flexion and extension. Let us examine that. From earlier discussion on PCL and ACL, if you haven't listened to that class, the link is given above just listen to that class that would help you really so when let us imagine for this situation that acl and pcl is made up of a rigid band that means they are rigid and of a constant length and we are we are oversimplifying that task but let us take it like that it is a rigid band now you see during flexion initial time of flexion the acl is of confined But when flexion is going to increase, you imagine that it is a rigid band, what is actually happening? The ACL which is attached from the femoral contaheil to this tibia is going to be stretched out. Right? It is going to be stretched out. So at this particular point, this ACL is going to be stretched out. And ACL actually prevents or ACL actually acts as a check to this motion. But when this movement is going to be continued, what actually happens is the ACL has a direction of fibers in this direction. The direction of fibers is this way, the direction of fibers is this way, the direction of movement is this way, the force produced is this way. If we divide that force component in a horizontal component and a perpendicular component, we see that the ACL's result in or the UCL supports Component is actually in this direction is in the anterior translator direction. So that will help the anterior translation of tibia. So femur is it clear? No. Let us imagine it again. You see that during the flexion of knee of the femur you need to have the rolling plus gliding. Okay now after some 25 degrees of pure rolling okay what happens the ACL becomes taut. At one stage it acts as a restraint but when it is this flexion is increasing you need to have this anterior translation right you need to have this anterior translation anterior glide of femur on during the flexion so what happens after some time when we reserve when we look into the force components of the ACL we see that the ACL initiates an anterior translation of femur So this anterior translation is actually helping. for assisting the anterior translation or glide anterior glide during the knee flexion we studied that during knee flexion there is anterior translation or anterior glide and posterior roll so this to assist this anterior raw anterior glide or anterior slide the acl is actually assisting acl is act actually assisting this anterior translatory motion okay it is acting as a check but after I said when the movement is being produced it produce an anterior translatory force on the fee for the femur and it initiates the anterior gliding similarly the piece here you see that at this one particular point female PCR is fine when extension is a film fraction to extension when extension is increasing PCL gets taught when PCL gets taught it will produce it's a force component will be in this direction the posterior direction right when in this is in positive direction the translatory component will be to this one and a perpendicular component will be into the joint axis that's actually causing compressing but we need to look at this translatory component this translatory component is actually producing a posterior translatory force this is actually aiding or assisting the posterior translation of femur during extension so this uh what we are going to see is what we are going to discover is that acl and pcl in fact actually help in the arthrokinematic movement inside the joint. Of course, they are acting as a restraint for anterior translation of tibia. That's another thing. But it is actually... ...in the arthrokinematic movement inside the joint. Now you can imagine if there is some damage to this ACL and PCL what can happen? The arthrokinematics inside the joint can get disturbed. The rolling can take place but the gliding... anterior glide cannot occur smoothly in anterior to ancillary push. We will discuss that in detail in the pathomechanics session. So that's all about the ACL and PCL dot. Let us examine that with the help of few diagrams. You can see the scenario of ACL and PCL. diagram shows clearly the role of ACL in flexion you know that when flexion is increasing the ACL gets stout considering it as a rigid band and you see the direction of fibers which is direction of force is in the direction of ACL fibers itself and now you resolve it into its component you can see that one component is vertically into the joint axis which is of course causing compression and of course you need not worry about that but about the other component which is directed outwards or anteriorly this component is initiating or causing anterior translation and this anterior translation in fact helps the anterior translation or anterior glide of the acl which is accompanying the flexion you know that flexion is accompanied by anterior glide and this is accelerated by the acl and here the pcl which has clearly shown in extension the fibers direction is shown the force direction is same as the direction of fibers it is having two components one component is into the joint axis and no need to worry about that the other component is providing a posterior directed force which will help or provide posterior translation this posterior translation help in the posterior glide of the femur during the movement of extension and it is in this way that the acl and pcl helps the arthrokinematic and osteokinematic movement of the knee joint now we are going to discover how menisci is helping in flexion and extension right you know that let us imagine for example this is the femoral condyle right this is the tibial condyle right and you know how the shape of the menisci the shape of menisci is like this okay menisci is thick in the periphery and thin in the central region that means it is having a wedge shaped wedge like shape from the lateral view this is having a wedge like shape in the center there is a less contact when the both sides that is thick one okay a wedge shape the shape so you you have here a wedge-shaped menisci yes you have here and here also right the wedge-shaped menisci now what is happening when flexion is initiated like this okay when the femur is moving for its reflection the initially that's no problem okay but what the femur should do the femur should actually climb the hill it should have an uphill motion on this meniscus it is not a straight one like this if it is straight one femur can move like this but it is an uphill motion femur has to move uphill should move an uphill motion and now you see that during this flexion during this movement femur has to move uphill so when it is moving uphill and this flexion is going to increase like this this menisci exert a force on the femur which is an oblique direction menisci on femur MF when we resolve that force into its component we see that there is a component like this and there is a translatory component you see that this is in direction of anterior direction anterior translation So what this Algeria translation will do. do like in the case of ACL this will also assist in the movement of femur this will also assist in the movement of gliding of the femur anteriorly so along with ACL this menisci also attaches or help or assist the movement of the femur similarly the femur should also exert a force on the menisci right that the femur exerts a force on the menisci and it is moving and you can saw that integers component you can see that what happens is this component of the force will actually compress the menisci like this and menisci is not a rigid structure and menisci will deform the menisci will deform in such a manner when femur is moving the menisci deforms like this menisci deforms like this so what happens ultimately is that during complete range of moment there is contact of menisci with the femur I don't know if it is rigid if it is a rigid structure the femur will slip off and menisci will be displaced anteriorly but menisci is attached very rigidly to the posterior horn we saw that the horns it is attached rigidly so menisci can move anteriorly instead menisci will get compressed like a sponge something like a sponge and this will ensure that there is always the femoral contact between the menisci this will always ensure that let's see with this what see when this is happening initially the menisci will be applied a force on the femur which is in this direction and resolving it will help in the anterior translation but when his femur is when femur is continuing downwards the femur will exert a force on the menisci this will cause the menisci to get compressed resolving this component you can see that it will cause the compression of the menisci or deformation of the menisci when this menisci is deformed it will always ensure that the femur is in contact the opposite happens in extension when extension what happens the menisci will get deformed anteriorly here this part menisci will get deformed and this part menisci will move up that means when extension is increasing this posterior deformation slowly vanishes it vanishes and vanishes and vanishes. and finally this is a situation when this is increasing the femoral force on the menisci is causing compression of the anterior meniscus anterior part of the meniscus why is it happening it is happening so that always there is a contact of menisci on the femur let us examine that with the help of you diagram here you can see the role of menisci the force mf denotes the force vector the force of menisci on femur you see the direction it is it can be resolved into its vertical component but component shown here the shear force one is actually helping the femoral motion and this translatory force anterior translatory force is what accompanies or facilitate the flexion of the femur where there is a natural anterior translation along with the rolling movement and the shear force 2 which is the femur on the meniscus is causing the deformation of the meniscus this both occur and help the femoral motion and here in extension the opposite happens In extension the opposite happens that is the force vector would initially resist or produce a posterior translatory force and the shear force will be on the anterior direction or anterior part of the meniscus which will cause its deformation. deformation. See the posterior translation of the meniscus or posterior movement and deformation is facilitated by the semimembranosus muscle along with semimembranosus the popliteus also play a role in this action. So this ensures that always there is a contact of menisci on femur and posterior translation of the menisci or posterior deformation of the menisci is of course accelerated by some muscles especially the semimembranosus muscle. You just saw the picture of the picture. that earlier right so this is what actually happened during the femoral motion of flexion and extension which you think that it is purely happening in the femoral is actually accelerated or facilitated by the motion of ACL facilitated by the motion of your menisci tune and the normal range of femoral motion is 130 degree about 130 degree of flexion right and you know that in some position like deep squatting you can increase up to 160 degree that is because of the body weight superimposed body weight and the continued motion as a complex so that can increase to 160 degree the normal range of motion possible is a 130 degree right and for normal level ground walking you need a knee flexion of 60 to 70 degree whereas for ascending a stair you need 80 degree of knee flexion right for normal level of ground walking you need 60 to 70 degree and now for ascending a stair you need 80 degrees of knee flexion and of course a person has a 0 to 5 degree or 5 to 10 degrees of knee extension an average of 5 to 10 degree of knee extension and if that is increased greater than that the condition is known as a genu recurvatum so genu recurvatum is a condition in ways the knee extension is increased greater than the normal. Normal value is 5 to 10 degree or of course 0 to 5 degree. 5 to 10 degree in particular and if it is increasing more than that it results in the condition known as genu recruitum. And of course there are many two joint muscles that are passing through the knee joint and this two joint muscles has an action on the knee flexion and extension. For example when hip is in neutral position imagine you are in a zip line lying position and hip is in a rotator position you go for knee flexion the knee new inflection is more but if uh hip is in extension position if hip is inflection position that knee flexion will be limited because of the passive insufficiency guess which muscle in particular rectus femoris due to the passive insufficiency in rectus femoris knee inflection will be limited for example you can try it down in prone position you go for knee flexion when hip is in neutral that's fine you can increase knee inflection but when hip piece inflection already the new flexion will be limited that is due to passive insufficiency in rectus femoris muscle and this is the example of passive insufficiency in rectus femoris muscle you can see that flexion in two position neutral and in already flexed position you can see the new flexion increase in range of motion in both we will look into detail about the pathomechanics in next session because time is running up so in this session in the next video we'll be discussing about the media rotation, data rotation, and the post-medium next-data. along with the pathomechanics of flexion and extension. So until then stay tuned and if you liked this video don't forget to click the like button and if you haven't subscribed to my channel kindly subscribe to the channel

If you wish to know any one in particular, the time codes are given below in the description and comment box, you can check on to that. Here we discuss the knee complex biomechanics, in particular the joint flexion and extension. Ticks in the knee joint that means the movements possible in the tibiofemoral joint we are focusing on the tibiofemoral patellofemoral we will discuss later in tibiofemoral joint we have three degrees of motions i told you earlier that is a flexion extension which are the principal motion or predominant motion abduction adduction of course varus and valgus and finally media rotation or lateral rotation or internal or external rotation.

When we evaluate the knee complex or any joint we need to have a joint axis for the motion to take place. But in human body we often discover that the axis is not a fixed one like a mechanical joint but it is an instantaneous one. Especially because the condyle or the surface articulating surface are not concurrent to each other.

That means in every degree of knee motion and every particular motion the axis is not fixed but an instantaneous axis of motion. The points of the axis constantly changes. And that makes the knee joint movements much more complex. Along with the three degrees of rotatory movements, we have three translatory motions that is the anterior and posterior gliding or translation, the medial and lateral translation and of course a pure spin and anterior displacement movements in the Nikon. We will discuss each one of them in particular but first we will focus on the flexion and extension and all the arthrokinematics, arthrokinematics means glide, slide, spin etc. as well as the osteokinematic movement, the flexion extension in particular and how this comes together to make a beautiful and a systematic movements possible in the knee complex.

before that let us look into the instantaneous axis of rotation of the knee complex. You can see here the instantaneous axis of femoral motion. I described it earlier that is the axis is constantly shifting. You can visualize different color schemes for the different levels of femoral motion, different degrees of femoral motion.

And according to that the axis is shown or it is constantly changing or we have an instantaneous axis of femoral motion for each degree of knee flexion and also for knee extension. Yes. and now we move on to the principal motion in the knee complex that is the flexion and extension flexion and extension the flexion and extension is the principal motion in the knee complex and for identify the motion we need to identify the axis the axis is an axis passing through both the femoral condyles both the femoral condyle It's a horizontal line passing through both the femoral condyles and we call that axis trans epicondylar axis. the movement in the knee complex that is a flexion and extension takes place in a trans epicondylar axis which is nothing but a straight line passing through the femoral condyle it's the lower end of the femoral condyles right and but as I told you the axis is instantaneous so this axis is not Fixed one it changes constantly during the knee motion But need not complicate that you just remember in your mind in knee joint motions The trans epicondylar axis is not a fixed one It is constantly moving just that you need to get into mind now. Let us look into the motion Looking into the motion.

We first need to remember it is a trans epicondylar axis passing through the femoral condyles epicondyles epicondyles right you just have to remember this in mind let it be in our mind now the first motion possible is flexion and then the extension let us evaluate this what is actually happening during flexion and extension you see that the femoral condyles are what you call convex and they are larger than the tibial condyles now for flexion to take place let us imagine a situation where the to tibia is fixed that means your tibia cannot move and femur is moving on the tibia there is an alternative like femur is fixed and tibia is moving but here we are going to take a consideration where fitibia is fixed and femur is moving can you give a real life experience a real life example for that that's our weight bearing position any of the weight bearing position team tibia is fixed and we can say that femur is moving that is for example in weight bearing you go for a squatting okay the tbi is fixed down there relatively fixed and the femur is moving okay so in that situation for example in squatting what happens is that for femur to move into the flexion okay for the hip to move into flexion or femur to move into flexion at the knee joint the femur should go backwards this is the flexion okay this is flexion here the tibia is flexed fixed and this is the flexion at the hip and knee right so this is the flexion and during this flexion The osteokinematic movement is flexion itself. Okay and what is the arthrokinematic movement? Femur roll downwards or rolls posteriorly. Right you can imagine this is what happening. This movement is known as the rolling of femur posteriorly.

Femur can roll anteriorly but if femur moves anteriorly, flexion won't happen. So femur should move posteriorly. Right that's the first point to guess to remember. And now what is happening Imagine this is a let us get into this let us imagine this is the tibia and you have the femur just look at this clause look at this picture in clause you imagine that the femur is only moving going for a rolling okay femur rolls on the tibial condyle you just see that after the rolling happens rolling happens rolling happens rolling happens and at one stage you see the femur will not be in a position of contact with the TBR condyle.

or the surface area on the tibial condyle gets finished that means femur cannot go in contact it should go like this okay can you guess it let us once again see that so imagine look at the lower end of the femur imagine what's the motion that is a rolling the flexion during flexion the femur you imagine a situation where femur is just rolling this is the rolling okay Just rolling like this rolling rolling rolling over rolling over rolling over rolling over and some degree of knee flexion you can see that Absolutely very little contact is only between femoral condyle and the tibial condyle and at this particular position Femur will be in a disadvantage. That is a disadvantage to the femur, right now How is it over come? This is overcome like this when femur is going to roll like this is okay After a few degrees of rolling, just look at this, after a few degrees of rolling posterior, this is the posterior rolling, what is going to happen? The femur is going to translate anteriorly.

That means slide or glide anteriorly along with rolling. So that at every point, there is actually enough contact between the femoral condyle and the tibia. Should I explain it once again? Let us see it.

So this motion is a disadvantageous one if there is roll alone. So in order to prevent that, in the fixed femur tibial content, the femur along with its rolling, the femur is going for an anterior translation. That means femur will go for an anterior glide.

And this anterior glide when it is accompanied by the posterior roll, there is a perfection so that femur can go to the highest possible flexion how many how much degree is possible it can go up to that much otherwise it would be limited let us see that again once again I believe you can see it right you see this is the rolling this is the rolling and during this rolling after a 25 degree of rolling that's how it is so 0 to 25 degree of flexion there is pure rolling itself okay only this motion only this motion after 25 degree of rotation just you can see that please look at the lateral condyle what is happening the femur motion will be accompanied by the sliding motion so that at all ways anterior slide will be induced so that at all ways there is a contact between the tibial condyle and the femoral condyle right the tibial condyle is a concave one this is convex one this is what happening in the convex concave rule that is when a convex is moving on a concave the arthrochiaromatics and osteochiromatics occur in the opposite direction here when the flexion is occurring and posteriorly in the posterior roll is occurring what is happening there is an anterior translation the glide is anteriorly in the anterior direction so that is how the motion of femur is being initiated in the knee complex that is in the tibio femoral joint so initially from 0 to 25 degree there is only translation only rolling 0 to 25 degree there is pure rolling alone and greater than 25 degree roll is accompanied roll is posterior posterior roll is accompanied by slide or glide it can be same okay slide or glide anteriorly see that's how the knee flexion is going to takes place let us examine that with the help of a diagram this is a scenario where we discussed about the squatting position that is femur is moving on a fixed tbm and you can see that friction which is shown by the red sign is actually rolling which is happening in the posterior direction whereas slide is shown it is alternating on as glide is shown in the anterior direction so this is what actually happening anterior slide as well as a posterior rolling or during squatting position whereas when we look at the squat to up that is getting up that is extension the anterior rolling is accompanied by posterior slide. So this diagram clearly illustrate the difference between anterior and next extension and flexion flexion is accompanied by posterior roll posterior glide and posterior roll and anterior glide whereas extension is accompanied by what you call the anterior roll and posterior slide or glide that's one scenario the squatting scenario is going for flexion okay now we are going for extension that is from squatting position you are getting up that is an extension which is opposite of flexion right yes what is happening the things are same but the femur is in flexed position and tibia is fixed for this consideration that is the person is in squatting he need to get up he is going to get up here a roll is coming anteriorly right the femur is going to roll anteriorly similar to earlier condition when there is a pure rolling there can be a problem like the tibial condyle's articulation is going to finish off and to prevent that what is happening the same mechanism Here there is a rolling. Here there is a rolling in initial degree. But after that, along with the anterior rolling, the posterior sliding takes place. And this initiates a complete flexion.

So along with rolling posteriorly, rolling anteriorly, here slide, here slide is going to happen posteriorly. So rolling anteriorly, sliding posteriorly. So that always this contact.

tails are in articulation so that is what happening in extension initially that is followed by a rolling and then it is followed by what you call a posterior anterior roll is accompanied by a posterior translation or posterior slide or glide that is how the motion of extension and the motion of flexion is taking place in the knee joint and now you see that after 25 degree there is a roll plus slide okay there is roll plus slide. So you can call it as a pure spin movement. That means after 0 to 25 degree or after initial degree of flexion and extension, the motion that is taking place in the femur is a pure spin motion. Spin can be called as a movement around an axis. This movement along with that in literature a movement combining pure amounts of same The same amount of rolling and gliding is also known as a spin moment.

So we call this as a pure spin moment. But if that is confusing just leave that and just check on to this. So during the position of weight bearing or during some examples like a squatting, when femur is fixed, sorry when tibia is fixed, the femoral motion of rolling takes place in one direction and the glide motion that is taking place inside the joint occur in the opposite direction. that is if flexion is occurring if flexion is occurring the gliding is occurring anteriorly if extension is occurring the gliding is occurring posteriorly all right i hope that is clear now let us move on to the second scenario where your femur is fixed your femur is fixed right here the scenario is different that is our femur is fixed yes what is a real life example For example, you are sitting in a table and you are extending your knee. Or the quartz table is an example of this one.

You are extending your knee, your femur is fixed and the only possible motion possible is the femoral, the tibial motion, tibial flexion and extension. Let us look back into this one. See this scenario Here the entire thing changes only the femur is, tibia is moving and femur is fixed. So you can fix it this one and there is no possible absolute movement possible. So during knee flexion that is during knee flexion that is the tibia should go for flexion.

The tibia should go for flexion okay. Now you imagine this is a concave on convex okay. This is a concave this gravity is concave on convex.

What should happen when there is an argyrokinematic and osteokinematic should occur in the same direction remember that. Now let us imagine, see when tibia is going for X flexion, what is happening? Let us imagine what is happening. For example in flexion of the knee at this position that is the tibia is moving.

When tibia is moving for flexion what is happening? There is the posterior roll, right? The rolling is of the posterior direction and along with you can just imagine look at this clearly along with that posterior roll.

Along with that posterior roll, the slide is also posteriorly. Right? Along with that posterior roll, let us fix it like this, along with that posterior roll, the slide is also posteriorly.

So that will help the motion to take place. But for example, you imagine this is going posterior roll, but if this is going for anterior slide, okay? Like the femur. For example, this is going for posterior roll.

and this is going for anterior slide if it is sliding anteriorly you can see that this joint will slip off or there is no concurrency or articulation between this one so in order to prevent that during this posterior rolling during this posterior rolling from this position the slide is also taking place posteriorly for example the slide is also going to the slide is also going to take place posteriorly see see this one slide and rod is posteriorly right the slide and rod is posterior the slide and draw is posteriorly you can see that right it is not uh rod posteriorly and anterior slide it is slide and rod in same direction that is explained by the convex concave surface moving on a concave one and along with that during flexion to extension this is the flexed position of the knee uh sorry always femur is moving femur is flexed and femur is fixed and knee is flexed okay now in this position the femur the tibia moves anteriorly along with that anterior translation or anterior slide okay just imagine this one see this how beautiful it is uh you see this is the situation and this is already a flexed knee and from this flexed knee um this should move for extension when it is moving for this roll see this one is the roll along with that this slide and teacher slide of course so when femur is moving on the fixed tibia the rolling and sliding is in opposite direction but when tibia is moving on a femur this both are in same direction that is from a tabletop knee extension when tibia is extending moving anteriorly when tibia is moving anteriorly that translatory movement that is a glide also occur anterior during a tabletop knee flexion when tibia is moving posteriorly when tibia is moving posteriorly the glide also occur posteriorly right all these are done to ensure that always there is a complete accuracy or concurrency between both of the joints. Let us see this with the help of few diagrams. You can see here that example described earlier the extension is followed by or accelerated by anterior translation that is in extension the anterior translation happens whereas in flexion you can see that flexion is accompanied by posterior translation.

So in cases like a femur is fixed the arthrokinematics and osteokinematics takes place in same direction. And now we move on to describe the role of ACL and PCL in knee flexion and extension. Let us move on to describe the role.

Yes, the role of cruciate ligament in flexion and extension. You know that we have anterior cruciate ligament and posterior cruciate ligament. And each of them are having a separate role in knee flexion and extension.

Let us examine that. From earlier discussion on PCL and ACL, if you haven't listened to that class, the link is given above just listen to that class that would help you really so when let us imagine for this situation that acl and pcl is made up of a rigid band that means they are rigid and of a constant length and we are we are oversimplifying that task but let us take it like that it is a rigid band now you see during flexion initial time of flexion the acl is of confined But when flexion is going to increase, you imagine that it is a rigid band, what is actually happening? The ACL which is attached from the femoral contaheil to this tibia is going to be stretched out. Right?

It is going to be stretched out. So at this particular point, this ACL is going to be stretched out. And ACL actually prevents or ACL actually acts as a check to this motion. But when this movement is going to be continued, what actually happens is the ACL has a direction of fibers in this direction.

The direction of fibers is this way, the direction of fibers is this way, the direction of movement is this way, the force produced is this way. If we divide that force component in a horizontal component and a perpendicular component, we see that the ACL's result in or the UCL supports Component is actually in this direction is in the anterior translator direction. So that will help the anterior translation of tibia.

So femur is it clear? No. Let us imagine it again. You see that during the flexion of knee of the femur you need to have the rolling plus gliding. Okay now after some 25 degrees of pure rolling okay what happens the ACL becomes taut.

At one stage it acts as a restraint but when it is this flexion is increasing you need to have this anterior translation right you need to have this anterior translation anterior glide of femur on during the flexion so what happens after some time when we reserve when we look into the force components of the ACL we see that the ACL initiates an anterior translation of femur So this anterior translation is actually helping. for assisting the anterior translation or glide anterior glide during the knee flexion we studied that during knee flexion there is anterior translation or anterior glide and posterior roll so this to assist this anterior raw anterior glide or anterior slide the acl is actually assisting acl is act actually assisting this anterior translatory motion okay it is acting as a check but after I said when the movement is being produced it produce an anterior translatory force on the fee for the femur and it initiates the anterior gliding similarly the piece here you see that at this one particular point female PCR is fine when extension is a film fraction to extension when extension is increasing PCL gets taught when PCL gets taught it will produce it's a force component will be in this direction the posterior direction right when in this is in positive direction the translatory component will be to this one and a perpendicular component will be into the joint axis that's actually causing compressing but we need to look at this translatory component this translatory component is actually producing a posterior translatory force this is actually aiding or assisting the posterior translation of femur during extension so this uh what we are going to see is what we are going to discover is that acl and pcl in fact actually help in the arthrokinematic movement inside the joint. Of course, they are acting as a restraint for anterior translation of tibia.

That's another thing. But it is actually... ...in the arthrokinematic movement inside the joint.

Now you can imagine if there is some damage to this ACL and PCL what can happen? The arthrokinematics inside the joint can get disturbed. The rolling can take place but the gliding...

anterior glide cannot occur smoothly in anterior to ancillary push. We will discuss that in detail in the pathomechanics session. So that's all about the ACL and PCL dot.

Let us examine that with the help of few diagrams. You can see the scenario of ACL and PCL. diagram shows clearly the role of ACL in flexion you know that when flexion is increasing the ACL gets stout considering it as a rigid band and you see the direction of fibers which is direction of force is in the direction of ACL fibers itself and now you resolve it into its component you can see that one component is vertically into the joint axis which is of course causing compression and of course you need not worry about that but about the other component which is directed outwards or anteriorly this component is initiating or causing anterior translation and this anterior translation in fact helps the anterior translation or anterior glide of the acl which is accompanying the flexion you know that flexion is accompanied by anterior glide and this is accelerated by the acl and here the pcl which has clearly shown in extension the fibers direction is shown the force direction is same as the direction of fibers it is having two components one component is into the joint axis and no need to worry about that the other component is providing a posterior directed force which will help or provide posterior translation this posterior translation help in the posterior glide of the femur during the movement of extension and it is in this way that the acl and pcl helps the arthrokinematic and osteokinematic movement of the knee joint now we are going to discover how menisci is helping in flexion and extension right you know that let us imagine for example this is the femoral condyle right this is the tibial condyle right and you know how the shape of the menisci the shape of menisci is like this okay menisci is thick in the periphery and thin in the central region that means it is having a wedge shaped wedge like shape from the lateral view this is having a wedge like shape in the center there is a less contact when the both sides that is thick one okay a wedge shape the shape so you you have here a wedge-shaped menisci yes you have here and here also right the wedge-shaped menisci now what is happening when flexion is initiated like this okay when the femur is moving for its reflection the initially that's no problem okay but what the femur should do the femur should actually climb the hill it should have an uphill motion on this meniscus it is not a straight one like this if it is straight one femur can move like this but it is an uphill motion femur has to move uphill should move an uphill motion and now you see that during this flexion during this movement femur has to move uphill so when it is moving uphill and this flexion is going to increase like this this menisci exert a force on the femur which is an oblique direction menisci on femur MF when we resolve that force into its component we see that there is a component like this and there is a translatory component you see that this is in direction of anterior direction anterior translation So what this Algeria translation will do.

do like in the case of ACL this will also assist in the movement of femur this will also assist in the movement of gliding of the femur anteriorly so along with ACL this menisci also attaches or help or assist the movement of the femur similarly the femur should also exert a force on the menisci right that the femur exerts a force on the menisci and it is moving and you can saw that integers component you can see that what happens is this component of the force will actually compress the menisci like this and menisci is not a rigid structure and menisci will deform the menisci will deform in such a manner when femur is moving the menisci deforms like this menisci deforms like this so what happens ultimately is that during complete range of moment there is contact of menisci with the femur I don't know if it is rigid if it is a rigid structure the femur will slip off and menisci will be displaced anteriorly but menisci is attached very rigidly to the posterior horn we saw that the horns it is attached rigidly so menisci can move anteriorly instead menisci will get compressed like a sponge something like a sponge and this will ensure that there is always the femoral contact between the menisci this will always ensure that let's see with this what see when this is happening initially the menisci will be applied a force on the femur which is in this direction and resolving it will help in the anterior translation but when his femur is when femur is continuing downwards the femur will exert a force on the menisci this will cause the menisci to get compressed resolving this component you can see that it will cause the compression of the menisci or deformation of the menisci when this menisci is deformed it will always ensure that the femur is in contact the opposite happens in extension when extension what happens the menisci will get deformed anteriorly here this part menisci will get deformed and this part menisci will move up that means when extension is increasing this posterior deformation slowly vanishes it vanishes and vanishes and vanishes. and finally this is a situation when this is increasing the femoral force on the menisci is causing compression of the anterior meniscus anterior part of the meniscus why is it happening it is happening so that always there is a contact of menisci on the femur let us examine that with the help of you diagram here you can see the role of menisci the force mf denotes the force vector the force of menisci on femur you see the direction it is it can be resolved into its vertical component but component shown here the shear force one is actually helping the femoral motion and this translatory force anterior translatory force is what accompanies or facilitate the flexion of the femur where there is a natural anterior translation along with the rolling movement and the shear force 2 which is the femur on the meniscus is causing the deformation of the meniscus this both occur and help the femoral motion and here in extension the opposite happens In extension the opposite happens that is the force vector would initially resist or produce a posterior translatory force and the shear force will be on the anterior direction or anterior part of the meniscus which will cause its deformation. deformation.

See the posterior translation of the meniscus or posterior movement and deformation is facilitated by the semimembranosus muscle along with semimembranosus the popliteus also play a role in this action. So this ensures that always there is a contact of menisci on femur and posterior translation of the menisci or posterior deformation of the menisci is of course accelerated by some muscles especially the semimembranosus muscle. You just saw the picture of the picture. that earlier right so this is what actually happened during the femoral motion of flexion and extension which you think that it is purely happening in the femoral is actually accelerated or facilitated by the motion of ACL facilitated by the motion of your menisci tune and the normal range of femoral motion is 130 degree about 130 degree of flexion right and you know that in some position like deep squatting you can increase up to 160 degree that is because of the body weight superimposed body weight and the continued motion as a complex so that can increase to 160 degree the normal range of motion possible is a 130 degree right and for normal level ground walking you need a knee flexion of 60 to 70 degree whereas for ascending a stair you need 80 degree of knee flexion right for normal level of ground walking you need 60 to 70 degree and now for ascending a stair you need 80 degrees of knee flexion and of course a person has a 0 to 5 degree or 5 to 10 degrees of knee extension an average of 5 to 10 degree of knee extension and if that is increased greater than that the condition is known as a genu recurvatum so genu recurvatum is a condition in ways the knee extension is increased greater than the normal. Normal value is 5 to 10 degree or of course 0 to 5 degree.

5 to 10 degree in particular and if it is increasing more than that it results in the condition known as genu recruitum. And of course there are many two joint muscles that are passing through the knee joint and this two joint muscles has an action on the knee flexion and extension. For example when hip is in neutral position imagine you are in a zip line lying position and hip is in a rotator position you go for knee flexion the knee new inflection is more but if uh hip is in extension position if hip is inflection position that knee flexion will be limited because of the passive insufficiency guess which muscle in particular rectus femoris due to the passive insufficiency in rectus femoris knee inflection will be limited for example you can try it down in prone position you go for knee flexion when hip is in neutral that's fine you can increase knee inflection but when hip piece inflection already the new flexion will be limited that is due to passive insufficiency in rectus femoris muscle and this is the example of passive insufficiency in rectus femoris muscle you can see that flexion in two position neutral and in already flexed position you can see the new flexion increase in range of motion in both we will look into detail about the pathomechanics in next session because time is running up so in this session in the next video we'll be discussing about the media rotation, data rotation, and the post-medium next-data.

along with the pathomechanics of flexion and extension. So until then stay tuned and if you liked this video don't forget to click the like button and if you haven't subscribed to my channel kindly subscribe to the channel

Transcript for:Knee Joint Biomechanics Overview

Transcript for:
Knee Joint Biomechanics Overview