 So, this is going to be a demonstration of the knee joint, the interior of the knee joint and the surrounding structures from the posterior aspect. This is the prone cadaver, this is the right side, I am standing on the right side and the camera person is on the left side. This is the posterior aspect of the propritial fossa, we have removed every structure. This is the upturned, reflected gastrocnemius, the medial head, the lateral head, upturned plantaris muscle and this is the soleus muscle. So, this muscle that you see here, this forms flow of the propritial fossa, this is the propritius muscle and we can see it is taking insertion from the posterior aspect of the tibia, right tibia above the soleal line, this is the soleal line. This propritius muscle as it goes upwards and laterally, I am going to show from under the structures of the propritial fossa, namely the neurovascular structures. We can see that the propritius muscle is moving upwards and laterally and here we can see it is dividing into two origins. The main origin goes up like this under the fibular collateral ligament and my instrument has gone under the fibular collateral ligament and it gets into the lateral femoral condyle and this is the one which separates the fibular collateral ligament from the knee joint and the other origin is to this structure here, this is the posterior part of the lateral meniscus. In this portion, it pierces through the posterior capsule of the knee which we have opened up and it goes under the arcuate propritial ligament on the posterior aspect of the knee which also we have opened out. So therefore, the propritius muscle has got two origins, one from the lateral femoral condyle which goes under the fibular collateral ligament and the other is from inside the knee from the posterior aspect of the lateral meniscus. The propritius muscle by virtue of its origin from inside the knee joint when it contracts it pulls the lateral meniscus away from between the femoral and the tibial condyle and therefore it reduces the chances of injury to the lateral meniscus. The other origin of the propritius which runs under the fibular collateral ligament and gets attached to the femoral condyle, it separates the fibular collateral ligament from the lateral meniscus and from the capsule of the knee joint and that is why the lateral meniscus is much less likely to be injured, much less likely to be torn. This is the arthroscopic view of a normal lateral meniscus and a torn lateral meniscus being repaired arthroscopically. Incidentally, we can also see that the fibular collateral ligament is a tight pod and it splits the insertion of the bicep femoris. This is the outturned cut end of the bicep femoris to the head of the fibula and this is the other end of the bicep femoris and we can see that the fibular collateral ligament splits the bicep femoris and gets attached to the head of the fibula. The action of the propritius, when the knee is extended not weight bearing, then it rotates the TBR 5 degrees medially, when the leg is weight bearing, then it rotates the femur 5 degrees laterally. So therefore, propritius muscle acts on rotation of the knee 5 degrees only when the knee is fully extended. So that is one of the actions, it also has to lock and unlock the knee. Now let's take a look at another structure. We see this muscle here. This is the semi-membranosis. The semi-membranosis as it descends down, it gets inserted onto the upper medial aspect of the TBR, but we can see it is giving an expansion here. This expansion is the one which reinforces the posterior capsule of the knee joint. Number one. Number two, we can see it gives an expansion which also reinforces the propritius fascia that also we can see and part of that we have split here. Number three, we can see it is giving some curved fibres which we have cut. This is the oblique propritial ligament and under that was another series of ligament which is also fused with the posterior capsule of the knee joint which we mentioned earlier called the arcuate propritial ligament. And under the arcuate propritial ligament, the fibres of the propritius enter into the knee and get attached to the posterior aspect of the lateral meniscus. This fibres that we see here, this is the posterior menisco femoral ligament which extends from the posterior aspect of the lateral meniscus and get attached to the medial femoral condy. The posterior menisco femoral ligament is another one of the intraarticular ligaments which holds the lateral meniscus in place. The next structure that we see here is what we have lifted up here. This is the posterior cruciate ligament. The posterior cruciate ligament has got two bands. One band goes little medially and another band goes a little laterally, the thinner band. This whole thing is the posterior cruciate ligament. The posterior cruciate ligament, it takes attachment from the posterior aspect of the tibial condy. And it goes up and gets attached to the lateral surface of the medial condy of the femoral. What is the action of the posterior cruciate ligament? When a person is walking downhill, there is a tendency for the femoral to slide forward on the tibia. And therefore, the posterior cruciate ligament prevents the forward sliding of the femoral on the tibia, especially when walking downhill. When the posterior cruciate ligament is torn, we can elicit it by means of what is known as the posterior drawer sign, where the patient is sitting with the knee partially flexed if we can push the tibia backwards, if we can push the leg back on the femoral. That is known as posterior drawer sign and it will be associated with pain. That is indicative of posterior cruciate ligament dead. In some dissections, we may be able to see a little bit of the anterior cruciate ligament here, but in this case, we cannot see it very clearly. The next structure which I would like to draw your attention to and it's rather unique, it's not very common is if you listen to me closely here, we can hear a bony sound. My instrument is hitting against a bony structure under the origin of the lateral head of the gastrocnemius and we can see, I have removed some of the fibres of the gastrocnemius here to show you that and I can, we can feel it also very clearly here. This is sesameoid bone within the lateral head of the gastrocnemius and that sesameoid bone is referred to as the favela and we can see that this particular cadaver has a favela. This is a lateral x-ray to show you a favela, a sesameoid bone within the lateral head of the gastrocnemius. These are some of the structures which I wanted to show you, what do you mean to the posterior aspect of the open out knee joint. Thank you very much for watching. Dr. Sanjeev, Sanyal, Sunny out. If you have any questions or comments, please put them in the comment section below. Mr. Ken Nol, Cumberbatch is the camera person. Have a nice day.