So, here in this video, we will study about the biomechanics of the knee joint. So, in our previous video, we have discussed about the biomechanics of the hip joint. So, now coming upon to the knee joint. So, we know that knee joint is basically a combination of the tibiofemoral articulation and the patellofemoral articulation. So, we will be discussing it one by one, starting with the tibiofemoral articulation. So, firstly, the alignment of the joint. So, from our previous video we know that we have the various mechanical and the anatomical axis of the bones and mechanical axis of the limb. So, starting with the femur, we have the mechanical axis of the femur from the center of the head of the femur to the center of the distal articulating surface of the femur. And we have the anatomical axis through the myelodiphysis to the center of the distal articulating surface of the femur. So, we have the different anatomical and the mechanical axis of the femur. Coming up on to the mechanical and the anatomical axis of the tibia, we have the center of the tibial plateau and we have the center of the ankle joint. So, the mechanical and the anatomical axis are basically aligned parallel in the tibia but they are aligned at an angle in the femur. So, beside these four axes we have the mechanical axes of the lower limb starting from the centre of the head of the femur to the centre of the ankle joint. So, the correlation of this axis to the knee joint tells us about the various deformities of the lower limb. So, normally this axis passes either through the center of the knee joint or the knee joint is slightly medial to this axis. Now, if the knee joint is drastically medial to this axis, there is a valgus deformity and if the knee joint is lateral to this axis, that means there is a varus deformity of the lower limb. So, continuing with the alignment part, so we have another diagram to explain it. the alignment of the knee joint. So we have discussed the mechanical axis of the femur from the center of the femur, head of the femur to the center of the distal articular surface of the femur. So this mechanical axis basically form a 9 degree angle to the central vertical axis. So, there is a 9 degree of angle which is a valgus angle. So, there is a 9 degree valgus angle of the mechanical axis of the femur to the vertical axis. Similarly, in tibia, the mechanical axis, it form a varus angle of 3 degree. So, here it was 9 degree of the valgus and here it is a 3 degree of varus. So, there is a resultant 6 degree of the valgus at the knee joint. So, this is the reason that the femoral component in the total knee replacement, it is placed in a 6 degree valgus position. Because we have a 6 degree of the resultant valgus at the knee joint. Now, starting with the various mechanism, the various mechanism involved in the Motion of the knee joint. So first is the screw-hole mechanism or which is known as locking or unlocking of the knee joint. So what does the screw-hole mechanism means? So it is basically external rotation of the tibia on the femur during the terminal extension. So while we are extending our knee joint, so in the final degrees of the extension there occur external rotation of the tibia. And similarly on flexing, starting to flex the knee joint, there occur internal rotation of the tibia during the knee flexion. So why does this occur? Because we have the basically anatomical differences between the lateral and the medial side. Starting with the tibial side, so we have the medial tibial plateau which is longer than the lateral tibial plateau. So in the medial tibial plateau, it is longer than the lateral tibial plateau. And similarly in femoral side we have a medial condyle which is larger and it extend distally than the lateral condyle. So this results in a that the there is a medial medially based pivoting of the knee joint. So the basically pivot of the knee joint is set in the femoral medial position, so there is internal rotation of the knee joint. So, what is the use of this screw-home mechanism or locking of the knee joint? So, on extension of the knee joint, there occur external rotation and the tibia gets locked in this position. So, this locking, what does this help? It decreases the work performed by the quadriceps while we are standing. So, this locking of the knee joint decreases the work of the quadriceps. Continuing with the screw home mechanism. So this is basically a question whether there is a movement of tibia occurring or it is a femur occurring so it depends whether it is open kinetic chain mechanism or it a closed kinetic chain mechanism so it depends whether we are sitting or we are standing if we are sitting our foot in in here that means it is open kinetic chain mechanism if we are standing that mean it is a closed complex our foot is on the ground and is fixed here our foot is free so if we are sitting so if we are sitting on terminal extension there will occur a external rotation of the tibia but if we are standing our tibia is fixed so on in those cases on extension there will occur a medial rotation of the femur on the tibia during the extension closed chain mechanism so there can occur a rotation of both it depends whether we are having a open kinetic chain mechanism that we are sitting or we are having a closed mechanism that we are standing So, another important is the rollback phenomena. So, this phenomena, it helps in basically flexion of the knee joint. So, in extended knee, this is the contact point. So, flexion of the knee joint, this contact point, it shifts posteriorly. So, there is a rollback of the femur, posteriorly on flexing the knee joint. knee joint. So why does it occur? Because of this posterior cruciate ligament. And what is the use of this rollback phenomena? That we are able to hyperflex the knee joint without impingement at this region. So similar funda is used in prosthetic design. That femoral rollback, it is a posterior translation of the femur with flexion. It is controlled by the to see a crucial ligament and what does it helps in it helps in the knee over knee flexion and it improves the quadricep function also so this was about the rollback of the knee joint now talking about the various features various now stability factors of the knee joint so we have the various stability factors which prevent the various and the valgus at the knee joint so to prevent the virus and the valgus we have the medial and the lateral collater ligament and to prevent the anterior translation we have the anterior crucial ligament and to prevent the posterior translation we have the posterior crucial ligament so that was about the tibio femoral component now coming to the patellofemoral part now to discuss the patellofemoral part firstly we should know the anatomy of the patella bone. Patella is a sesamoid bone. So as we all know in the quadriceps tendon, so we have it has a rough superior surface or the anterior surface. We have a base where the quadriceps is attached and we have the apex which is a attachment of the patellar ligament. Posterior surface we have two articulating facet. We have a larger lateral facet and we have a smaller medial facet. And the apex it is a non articulating part. It doesn't articulate. So why there is a use of patella? Why it is in our body? Because it increases the liver arm of the body. So if this is the center of rotation of the knee joint. So, this is the pull of the quadriceps, this is the pull of the patella tendon. So, the presence of the knee patella, it increases this liver. So, increased liver arc motion is there because of the presence of the patella joint. So, if the patella, in cases where the patella is removed, there occur a decrease in the strength of the extension because the liver arc motion is The length of the liver arm is decreased. This is the reason of the use of the patella in our body. Talking about the patellofemoral joint. So, it has a sliding articulation that in various degrees of flexion and extension it articulates differently and the maximum we will discuss it in a shorter while. So maximum contact between the femur and patella is at a 45 degree of flexion and the primary function of the patella is basically to increase the liver arm of the extensor mechanism of the knee joint thus improving the efficiency of the quadricep contraction. So that we have already discussed. So, in patellofemoral joint we have an important angle which is by the name of Keu angle. So, Keu angle is basically angle between the, it is extension of the anatomical axis of the femur that is line from the anterior spiral like spine to the center of the knee joint and then second line is from the the center of the base of the patella to the tibial tubercle. So, this forms an angular roughly. 13 degree in the male and 18 degree in the females. So KO angle is angle between the line from the anterior superior spine of the ilium to the middle of the patella and then a line from the middle of the patella to the tibial tuberosity. Basically, males have a shorter angle, females have a larger angle. So it indicates the valgus angle. So KO angle of more than 20 degree, if it is there, it creates an abnormal pull at the patella. It creates excessive lateral pull of the patella. So, talking about the articulation, so we have discussed that patella basically articulate differently in various motion. So, in zero degree of the flexion that is in a full extension. So, patella is lying here at a proximal extent of the femur. So, on progressive flexion of the knee joint, the articulating surface of the trochlea changes with the patella. It moves more distally. So, a 30 degree of flexion, this is articulating surface, 60 degree, 90 degree and in a full flexion that is 120 degree, only the two condyles articulate with the patella. So, similar in the patella, it is the inferior part that is articulating here in full extension and on flexion of the knee joint, there occur involvement of the superior part or the proximal part of the patella. So, here at 120 degree of flexion, it is the proximal or the superior part of the patella which articulates here with the two condyles. So, this is about the patellofemoral articulation. So, here in 20 degree, it is the inferior part of the patella articulating. And in full flexion 135 or 120 it is the superior and the two facet part articulating with the two condyles of the femur. So this was about the patellofemoral stability. the articulation of the patellofemoral joint. Now lastly, talking about the various stability factors. So, what all provides the stability? We have the various ligaments which provide the stability of the patellofemoral joint. So, we have the various ligaments. We have the most important of them is the medial patellofemoral ligament which prevents the lateral displacement of the patellofemoral joint. patella because of the KO angle. So we have discussed the KO angle which creates a lateral pull at the patella. So this important ligament which is the medial patella femoral ligament it prevents the lateral displacement of the patella. So that was the roughly about the biomechanics of the knee joint. So thank you for watching the video.