 This is a quick demonstration of the distinction of the posterior compartment of the leg. This muscle that you see in front of us, this is the gastrocnemius. The gastrocnemius has got two bellies. We can see the medial belly and the lateral belly. The medial belly is bigger than the lateral belly. It takes origin from the posterior aspect of the medial condyle of the femur and the posterior aspect of the lateral condyle of the femur. The two bellies unite and approximately midway they become a flat aponeurotic band and further down they rapidly converge to form the tendogalcaneus. So this is the gastrocnemius. A few quick words about the gastrocnemius. The gastrocnemius is type 2 white muscle. So it is for running, jumping, sprinting and for rapid actions. It is easily fatigable. The medial belly is the one which is maximum prone to stresses and strains and tears and that tear of the medial belly is referred to as tennis leg. The medial belly of the gastrocnemius is also sometimes responsible for compression of the propyteral artery and that is known as propyteral artery entrapment syndrome. And under the medial belly of the gastrocnemius we have a bursa which we can see here, a remnant of that bursa. This is the bursa of the gastrocnemius which communicates with the knee joint. So these are some aspects of the gastrocnemius which is in the superficial compartment of the posterior. Now I am going to split open the gastrocnemius and separate it from the underlying muscle and that is the soleus muscle. The soleus is a flat muscle. This is type 1 red muscle. It is a sustained action muscle. It is not easily fatigable. So it is said that you run with your gastrocnemius, you stroll with your soleus. Look at the attachment of the soleus to the posterior aspect of the tibia. It has got an inverted V shaped attachment. This is referred to as the solial line. So the soleus is attached to the solial line below and attached to the solial line from above is this other muscle which is the popliteus muscle which I shall tell just a little later. So this is the inverted attachment of the soleus and in between the fibula and the tibia there is a portion where the soleus line is absent. Instead there is a fibrous arch and that is known as the tendinous arch of soleus under which the popliteus vessels pass and they can get compressed here in this side and my finger has gone under it but I will show it to you when I reflect the soleus. In this particular cadaver we have what is known as an accessory soleus and we can see that here which is usually present here. Normally the soleus tendon should stop here and the rest of it should be the only the tendu calcaneus. Under the lateral head of the gastrocnemius we have yet one more muscle which is attached to the upper part of the lateral condyle of the femur and that is this muscle here which I have shown picked up here. This is a very small muscle which is called the plantaris. Immediately as it passes between the two heads of the gastrocnemius this is the plantaris muscle it becomes a long thin tendon and it runs from lateral to medial between the gastrocnemius and the soleus. This is the plantaris and it merges with the tendu calcaneus. This has got this does not have any much clinical anatomical significance and the only clinical significance is that sometimes it can rupture and then it produces again what is known as a tennis leg. This is to be called a freshman's nerve because in the earlier days some people used to mistake this for the tibial nerve. Most important point is that this is used for nerve drafting the plantaris. Now let's say a few quick words about the tendu calcaneus. The tendu calcaneus is arguably one of the most powerful tendons in the human body and it is the only large tendon which is not covered by synovial membrane. Instead it is covered by a sheath part of which is retained here and that is known as the paratinum. It occupies almost the lower half of the leg and it is a combined insertion of the gastrocnemius, the two heads, the soleus and of course the plantaris. This is inserted onto the posterior aspect of the calcaneus and there is a bursa between the tendon and the calcaneus that is known as the subtendinous bursa or that and there can also be a bursa on the under surface on the between the skin and the calcaneus that is known as the superficial and they can be inflamed in what is known as calcaneal bursitis. This tendu calcaneus fibers as they converge they rotate 90 degrees laterally so therefore the fibers coming from the gastrocnemius they are oriented laterally and the fibers coming from the soleus they are oriented medially. The purpose of this rotation is to add extra springiness to the gait. This is such an important tendon and this is a very powerful plantar flexor of the foot one of the most powerful plantar flexors. At this juncture I would like to take a step back and mention that soleus is a single joint muscle because it is taking origin from the tibia and the fibula but the gastrocnemius is a two joint muscle because it is taking origin from the femur so therefore the gastrocnemius apart from its plantar flexion action it is also a flexor of the knee joint but it cannot do both actions together to the full extent therefore if the knee is fully flexed 90 degrees then the gastrocnemius cannot plantar flex the foot. So come back to the action of the soleus to the tendu calcaneus it is one of the most powerful plantar flexors and if there's an injury of the tendu calcaneus it is as bad as cutting the foot. So therefore repairing the tendu calcaneus after it is torn is mandatory and when it is torn we usually repair it in the way I have shown it here we make a z-shaped incision we do not repair it directly end to end because if we repair it end to end it will tear again so instead we repair it in the form of a z and that's known as a z plus t that way what happens is the line of tension is distributed and then it is not likely to rupture again. So now let me reflect the soleus with the tendu calcaneus and once I reflect it we see the deep layer of muscles of the back of the foot and before I proceed any further I have inserted my finger under the tendu calcaneus arch of soleus and you can see it is coming out from here and we can see that the tibial nerve the popliteal artery and the popliteal vein they are all passing from the popliteal fossa under the tendu calcaneus arch of soleus into the back of the leg and this is the place where the popliteal artery can get entrapped. So now let's take a look at the structures that we can see in front of us this structure that we see here this is the tibial nerve this tibial nerve supplies all the muscles of the posterior compartment the leg it runs in the deep compartment and this is where it can undergo what is known as a compartment syndrome then we have this structure here this is the posterior tibial vein and this is the posterior tibial artery and as we go lower down we can classically see that the posterior tibial artery is accompanied by the vena cometantis one on this side and one on this side and we can see that this vena cometantis they've got multiple openings these are all the places where the perforating veins were opening and they unite and they form the posterior tibial vein so this is about the posterior tibial artery the posterior tibial vein and the tibial nerve and these are the various branches of that now let's take a quick look at the structures which pass through the under the flexor retinoculum that is the retinoculum between the medial malleolus and the calcaneus this is bridged by the flexor retinoculum and this space is referred to as the tarsal tunnel this tarsal tunnel is the place where the tibial nerve can be compressed and it can lead to what is known as tarsal tunnel syndrome the muscles that we see in the posterior compartment are on the back of the leg going from medial to lateral we have there's a vertical line on the back of the tibia medial to that is the flexor digitorum longus lateral to that is the tibialis posterior and the lateral most is the flexor halusis longus but as these muscles go down the orientation changes somewhat and we can see it here in the tarsal tunnel the anterior most structure is this one this is the tibialis posterior tendon this tendon that we can see here this big tendon the next one is the flexor digitorum longus then we have the posterior tibial artery with its accompanying vena commitantes then we have the tibial nerve and finally we have the flexor halusis longus so therefore there is a very quick mnemonic here we have tom tibialis posterior dick flexor digitorum longus bloody tibialis posterior tibial artery and vein nervous tibial nerve and held flexor halusis longus these are the structures which are passing through the tarsal tunnel now let me mention a few quick words about this popliteus muscle this is also a muscle of the deep compartment and as i mentioned it takes attachment above the solial line below the solial line is the solius it goes from medial to lateral up like this and it gets inserted onto the lateral condyle of the femur the popliteus muscle forms the floor of the popliteal fossa the lower part of the floor it is also supplied by the tibial nerve tibial nerve runs like this and the nerve supplies from inner aspect the popliteal muscle acts as a rotator of the knee by five degrees only when the knee is extended it helps to lock the knee and helps to unlock the knee so this is the most important action of the popliteus muscle so these are all the points which i wanted to mention in the posterior compartment the superficial in the deep if you have any questions or comments please put them in the comment section below Dr. Sanjay Sanyal signing out have a nice day