 Good day everybody. This is Dr. Sanjay Sanyal, Professor of Department Chair. This is going to be a demonstration of the muscles and the ligaments on the posterior aspect of the knee with certain special movements which are associated with these ligaments and muscles and also associated structures in the propritial fossa and the back of the leg. So this is the left knee that you see in front of you. This is the whole femur. This is the left knee joint and there's the upper part of the leg here on the left side and we have put for comparison We have put the right side here. So we shall focus on the left side. So first let's take a look at the muscles which are attached to the back. Remember red is the origin, blue is the insertion. So we see this one here. This is the insertion of the doctor tendon. The doctor tendon comes straight from the ischial tuberosity and gets attached to this bone here. This is the adductor tubercle. This adductor tubercle is an elevation which you can feel on your medial condyle of a femur. It is in the region of the medial epicondyle and this is where it gets inserted. It is shown a little away. This is the insertion. So this is the insertion of the adductor tendon, the hamstring component of the adductor magnets. This is the origin of the medial head of the gastrocnemius. Gastrocnemius medial head forms the intromedial boundary of the propritial fossa. Here we see the origin of the lateral head of the gastrocnemius and we can see this is the origin of the plantaris. Inside the lateral head of the gastrocnemius there can be an isosemoid bone which is referred to as the favela. This is the lateral extreme of the knee to show the isosemoid bone called favela within the telenoid origin of the lateral head of the gastrocnemius. We can see another origin below that. This is one of the origins of the popliteus muscle. The other origin of the popliteus muscle is from inside the knee joint. There is an opening in the posterior capsule of the knee joint. It takes origin from the posterior limb of the lateral meniscus of the knee. Then we see this blue portion here above the soleal line. This is the insertion of the popliteus. The popliteus takes origin from the upper lateral side and it moves down and medially and gets inserted. Therefore the popliteus muscle and the popliteus fascia covering it forms the floor of the lower part of the popliteal fossa. We see this insertion here. This is the insertion of the semi-membranosis muscle. The semi-membranosis muscle as you know along with the semi-tendinosis it forms the supromedial boundary of the popliteal fossa. This semi-membranosis has got an extensive expansion. Apart from its main insertion on the back of the upper tibia, it reinforces the posterior capsule of the knee like this. It also gives a ligament called the oblique popliteal ligament which runs like this. It runs from the middle side up towards the lateral side. That's called the oblique popliteal ligament. It also gives an expansion which reinforces the popliteus fascia. So these are at least three expansions of the semi-membranosis that are very clearly established. Between the insertions of the semi-membranosis and the origin of the medial head of the gastrocnemius there can be a bursa. That is known as the semi-membranosis bursa. Similarly under the origin of the medial head of the gastrocnemius there can be a bursa that is known as the gastrocnemius bursa. Both these bursa as well as the popliteus bursa which is between the popliteus muscle and the knee joint. In these three bursa they can communicate with the knee joint. And if they rupture they can also form a collection in the popliteal fossa which is referred to as the modern baker's cyst. This is an MRI of the knee to show a popliteal cyst also known as the modern baker's cyst located in the popliteal fossa. So we have seen the muscles around that region. Now let's take a look at the ligaments. Two most important ligaments are the tibial collateral ligament on the tibial side that's the medial side and the febular collateral ligament which comes on the lateral side. So first let's take the tibial collateral ligament. The tibial collateral ligament takes origin from the medial epicondyle of the femur. It's a flat band, a tight flat band and it runs down like this. Here it is fused to the left side of the knee joint and here it is also attached to the peripheral margin of the medial meniscus. And then it gets attached here to the upper medial aspect of the tibia. There can be a bursa between this tibial collateral ligament and the tibia itself. And additionally there can be a bursa between the tibial collateral ligament and this insertion of the pesancerinas that is referred to as the ancerine bursa. The pesancerinas is the combined insertion of the sartorius, gracilis and semitate dinoces. For that I have turned the tibia slightly to show you. So that is the tibial collateral ligament. And because it is fused to the peripheral margin of the medial meniscus, the medial meniscus is relatively immobile. And that is one of the reasons why medial meniscus stares are much more common than the lateral meniscus stares. Now let's take the other ligament, the febular collateral ligament. For that I am showing the lateral side. The febular collateral ligament takes origin from the lateral sphemicondyle of the femur. And it goes down and it gets inserted onto the head of the fibula. And as it gets inserted it splits the insertion of the biceps femoris. And we can see this blue structure here. This is the insertion of the biceps femoris which incidentally forms the supralateral boundary of the paupitial fossa. And it splits that insertion so that the insertion of the biceps femoris forms a U all around the febular collateral ligament. This febular collateral ligament is separated from the knee joint and from the lateral meniscus by the paupitius tendon which I mentioned just a little while back. The febular collateral ligament therefore is not attached to the lateral meniscus. And because the febular collateral ligament is free from the lateral meniscus, plus the fact that the lateral meniscus also gives partial origin to the paupitius muscle, the lateral meniscus is much less commonly injured during rotation of the knee. Because during rotation of the knee the lateral meniscus is pulled away by the paupitius and therefore it is prevented from injury. Though it does get injured occasionally as a peripheral tear, but it is much less common than injury of the medial meniscus. There is also an archivate paupitial ligament. It starts from the head of the febular, it arches like this upwards and medially and it forms an opening under which the paupitius muscle emerges. This ligament is supposedly inversely related to the presence, size or the absence of the sesame bone which is present inside the lateral head of the gastrocnemius, which I mentioned earlier, the febular. It is postulated that these two structures ligament as well as the febular are concerned with maintaining the posterior lateral stability of the knee joint. This is another lateral x-ray of the knee to show febular and sesame bone within the lateral head of the gastrocnemius. Now let's come to a very special movement which is present in the knee and that is the rotation movement because everybody understands that the knee is a hand joint and therefore flexion and extension movement is something which everybody understands. What is poorly understood is that the knee is also capable of rotation. Rotation is defined as rotation of the tibia and that is measured by the direction the second toe is pointing. Usually when the knee is flexed to 90 degrees, the tibia can rotate 10 degrees immediately and can rotate 30 degrees laterally. When the knee is extended, the tibia can rotate 5 degrees immediately. How is this achieved? So let's take a look at the same muscles. Coming back to the muscles in the supramedial boundary of the optical fossa, we have the semi-membranosis and the semi-tendinosis. I told you this was the insertion of the semi-membranosis and I showed you this was the insertion of the semi-tendinosis. So these two muscles, the semi-membranosis and the semi-tendinosis are responsible for medial rotation of the tibia by 10 degrees when the knee is flexed to 90 degrees. Similarly, I told you this is the insertion of the biceps femoris to the head of the fibula. This is responsible for 30 degrees of lateral rotation of the tibia when the knee is flexed to 90 degrees. Now the question is why does the tibia rotate only 10 degrees immediately and 30 degrees laterally when the knee is flexed? Here the role of the cruciate ligaments come into play. Antean and the posterior cruciate ligaments. When the tibia, when the leg is rotating immediately, the antean and the posterior cruciate ligaments, they twist more tightly. And so therefore they limit medial rotation. And that's the reason why medial rotation is only 10 degrees and when the leg is laterally rotated, these ligaments un-twist and therefore lateral rotation is to a greater extent. That brings us to the other roles of the paupritis itself. One role of the paupritis I have already told you is to move the lateral meniscus away during rotation and therefore prevent it from injury. The paupritis also plays a role in rotation of the tibia. It helps to lock the knee when standing and in this it is helped by the cruciate ligaments. The paupritis also helps to unlock the knee, the extended knee before flexion so that we can sit down. And this again there are two aspects to this. When the leg is touching the ground, that is referred to as the closed kinetic chain. In such a situation obviously the tibia cannot rotate. In such a situation the paupritis rotates the femur 5 degrees laterally. On the other hand when the leg is lifted away from the ground that's called open kinetic chain. In such a situation the paupritis rotates the tibia 5 degrees immediately. So the paupritis acts on the knee to rotate the leg only when the knee is fully extended. And you may have heard of the childhood prank where in a person standing straight and you tap him from behind and he falls down. It is because you are stimulating the paupritis muscle and therefore causing the paupritis muscle to unlock the knee by rotating the femur and therefore he falls down. Knee flexes involuntarily. So these are the tendons, the muscles, the ligaments and the movements which are possible on the back of the knee. More will follow when I come further lower down and show you the back of the leg. Thank you very much for watching. Dr. Sanjay Sanyal signing out. Please like and subscribe. If you have any questions or comments, please put them in the comment section below. Have a nice day.