 Good day everybody. Dr. Sajja Sanyal, Professor Department Chair. This is a supine cadaver. This is the right forearm. I'm standing on the right side. Camera person Mr. Sherwin Weeks is also on the right side. We shall be demonstrating the extensor aspect and the muscles and the extensor aspect of the forearm. So let's start with this structure here. This is the supinator muscle. The supinator muscle, as you can see, it takes origin from deep inside from the supinator crest of the alma and it wraps around the radius from the posterior aspect, lateral aspect and the anterior aspect and it covers the entire surface of the radius above the anterior and posterior oblique lines. This supinator muscle, as you know, is a supinator of the forearm in any position of the forearm, whether it is flexed or extended, unlike the biceps, which can supinate only when the forearm is slightly flexed. Now this supinator muscle is pierced by this nerve. This is the radial nerve. This is the deep branch of the radial nerve and we can see it is going under a fibrous arch. This fibrous arch is located in the superficial proximal aspect of the supinator and this fibrous arch is referred to as the arch of frosty. The radial nerve can get potentially entrapped in this fibrous arch of frosty to produce what is known as the supinator entrapment syndrome. And if you were to look here, you will find that the radial nerve is coming deep. Here it has become the posterior introsius nerve and I have picked up the posterior introsius nerve here. So supinator muscle is split into a superficial and a deep part by this radial nerve. The next muscle of the extensor compartment is this muscle that we see here. This is the brachioradialis. The brachioradialis is ideally supposed to take origin from above the lateral epicondyle and this is the lateral epicondyle where my thumb is located. But this has got an anatomical variation. It is taking an extensive origin from above the lateral epicondyle and from this lateral supracondyle ridge and it is also merging with some of the fibres of the triceps. The brachioradialis in this particular cadaver is continuing down and it had also shared fibres with this muscle which I have to tell you just a little while later. And the muscle then becomes the flat thin tendon which gets inserted just above the stellar process of the radius. Now the important thing about this brachioradialis is that it is a flexor of the forearm even though it's a muscle of the extensor compartment, it flexes the forearm weakly when the forearm is semi-pronated like this. Therefore if there's a paralysis of the flexors of the forearm brachioradialis can still weakly flex the forearm. Undercover of the brachioradialis we have two structures and I'm going to show the two structures to you right now. This is the first structure. This is the radial artery which runs under cover of the brachioradialis. We have completely separated out and the second structure is this one here. This also was running under cover of the brachioradialis. This is the superficial division of the radial nerve. This responses under the tendon of this brachioradialis and then it supplies the skin on the dorsal aspect of the hand and we can see the branches. One branch is going to the thumb, other branch was going to the dorsal aspect of the hand. So we have retracted this side. This is the place where we just above the radial stellar process that we tap with the knee hammer to produce what is known as the brachioradialis reflex jerk. Next muscle that you see which is taking origin from the lateral epicondyle is this muscle here. This is the combined origin of the extensor carpyradialis longus and the extensor carpyradialis grievis which get inserted on to the base of the second and the third carpyradialis respectively. This extensor carpyradialis is one of the superficial muscles and this is the basis of certain tests which I shall describe just a little while later which is applied in the cases of lateral epicondyleitis also known as tennis elbow. To continue with the other muscles in the extensor aspect, we see this muscle. This muscle is also taking origin from the lateral epicondyle. This is the extensor digitorum and we can see the fibers are breaking up into four tendons. In this particular cadaver it is breaking up into three tendons. Ideally it should break up into a fourth tendon. This is the extensor digitorum. Some books call it the extensor digitorum comedis. You can see the tendons are going to the index finger, middle finger and ring finger and one tendon should also go to the little finger. I shall mention the tendons through which they pass just in a little while. Another muscle that we can see in the superficial compartment of the extensor aspect is this muscle here. This is the extensor carpyradialis which is also taking origin from here. So these are the three superficial muscles of the extensor compartment that we can see here. This lateral epicondyleitis which I mentioned just a little while back also called the tennis elbow is quite a common condition when there is no specific inflammation of the common extensor origin of these muscles. And these muscles are the basis of certain stress tests. One of them is called the Mil's test which is used to stress the extensor carpyradialis brevis and the longus. Then there is another test called the Kozen's test which also stresses these extensor carpyradialis longus brevis and extensor carpyranaris. And there is a third test called the Monsley test which stresses the extensor digitorum. Now we shall go a little deep. I am going to retract this muscle and I am going to show you these muscles taking origin. This is the first deep muscle. This is taking origin from deep under these muscles and we can see it is crossing over the extensor carpyradialis longus and brevis. This is the combined origin of the abductor polisus longus and extensor polisus brevis. Now here we have something very interesting. This abductor polisus longus. As we know the word longus means it is a long muscle. Obviously this is a long muscle that is why it is called abductor polisus longus. But here we find that it is getting inserted onto the base of the metacarpal bone. We do have an abductor polisus brevis on the thinner eminence of the thumb and we can see that here. The abductor polisus brevis is a small muscle that is why it is called a brevis but it is getting inserted onto the radial aspect of the thumb, proximal phalanx of the thumb. So here there is a potential contradiction. A longus muscle is inserted proximally and a brevis muscle is inserted distally. Both these are abductors of the thumb. The first one abductor polisus longus it abducts it at the carpo metacarpal joint. Abductor polisus brevis abducted at the first metacarpal phalangeal joint. The next one is the extensive polisus brevis. And we can see it is shedding fibres with the abductor polisus longus and it is continuing down to the base of the proximal phalanx of the thumb. This is the extensive polisus brevis. We do have a counter opposite muscle on the thinner eminence that is the flexor polisus brevis which is inserted onto the base of the proximal phalanx through the radial sesamoid bone. These two muscles they form the lateral boundary of this cavity here which is called the anatomical snub box. The next deep muscle that we can see here is this one here. This is the extensive polisus longus and we can see this after taking origin it makes a sharp angle. This angle is made around this bori prominence here where my thumb is located. This is called the dorsal tubercle of blister on the dorsal aspect of the radius. And here it makes an angle and it gets inserted onto the distal phalanx of the thumb. This forms the medial boundary of the anatomical snub box. So therefore this is the anatomical snub box. Now this region has got plenty of clinical correlations. Let me mention those clinical correlations after I have described the content. I have picked up this structure here. This is the radial artery. Radial artery as I told you it runs under cover of the brachioradialis and we can see it running. And then it goes under the abductor polisus longus and the extensive polisus brevis. It comes to the anatomical snub box. It crosses here and then it passes through the first dorsal introsius. This is the first dorsal introsius and then it goes into the palm where it forms the deep palm arch. There is a condition which involves these tendons. The abductor polisus longus and the extensive polisus brevis that is called washer woman's hand. In earlier days washer women used to wring the clothes and therefore this to get nonspecific inflammation of this. Nowadays of course nobody uses their hand to wash clothes because everybody uses washing machine. But people still call it gamer's thumb, laparie thumb, texting thumb. Nonspecific inflammation of this is called decurban's tino cyanobitis. Inflammation of this tendon, extensive polisus longus is called drummer's wrist. Because the tendon makes a sharp bend here and it gets inflamed when the person keeps using the thumb. Musicians use it for long hours. Let me now come to the extensor digitorum. As I said extensor digitorum is running through this tunnel here. And it is breaking up into three. It should break up into four tendons. We can see these connecting bands. These are inter-tendonous junctions. These help to hold the tendons together and prevent them from playing out and helps to coordinate the action of these tendons. Accompanied this extensor digitorum on the deep aspect we can see yet one more tendon which is coming from all on our side of the tendon to the index finger. This is a separate muscle and we can see this muscle is this one here. This is the extensor indices. This is also one of the deep muscles and it also goes to the extensor tendon of the index finger. Likewise, the little finger also has got its own separate tendon. In this particular cadaver both the tendons are coming together through a separate tunnel. This is the extensor digiti minimi. So this is considered as the tendon of the extensor digitorum and the other one is considered as the extensor digiti minimi. Though in this particular cadaver as I said both of them are running through one separate tunnel. Let's take a look on the torso aspect of the wrist. We can see this tough fibro structure here. This is what is known as the extensor retinaculum. I have cut out the extensor retinaculum in certain places to show the tendons. Extensor retinaculum was a tough sheet of fascia which was a continuation of the anti-barricle fascia. It was attached laterally to the radius and it went obliquely up like this and we can see the remnant of that and it went medially and it got attached to the carpal bones namely the pisiform and the trichotron. Under this there are six tunnels and each of those tunnels are occupied by one or more tendons with their sonovir sheets. So let's take a look at those tunnels. The first tunnel is this one which I mentioned forms the lateral boundary of the canada beaker snuck box. That is the abductor policies longest and extensor policies bravest and we can see the tunnel here. This is the first tunnel. I have split open the extensor retinaculum to show you the tunnel. It was located here. The second tunnel is this one here and I have split it open to show you. This is occupied by the extensor carpal radius longest and extensor carpal radius bravest. Then we have a third tunnel which also have split open and this is that third tunnel. This was occupied by extensor policies longest. This is the one I said is responsible for what is producing drummer's wrist. Then we have a fourth tunnel and this tunnel is located here. We can see this tunnel here which I have split open again. This is occupied by the extensor digitorum extensor indices. But in this case as I mentioned there was an anatomical variation. The tendon to the little finger is not passing through this tunnel. Then we have a fifth tunnel and that is occupied by the tendon to the little finger and the extensor digiti minimi in this particular cadaver. But in another person this tunnel will be occupied only by the extensor digiti minimi. Last but not the least we have this tunnel here. This is occupied by the extensor carpal radius. So these are the six tunnels which are located under the extensor retiniculum and each of these tendons are lined by sign of a sheet so as to reduce friction. So this is what we see in the dorsal aspect of the wrist under the extensor retiniculum and further distally we can see the tendons going to the dorsal aspect of the fingers. I have split open the dorsal aspect of the middle finger to show you how these extensors go. They form an expansion which is called the dorsal digital expansion or naponiotic expansion. And then they split into three bands. The median band gets inserted onto the middle phalanx and the two lateral bands they go and get inserted onto the distal phalanx. Rupture of this distal phalanx band can produce what is known as a mallet finger where the distal phalanx will not be able to be extended by the patient. That happens in baseball players, in basketball players and it can happen also in housewives when they are tucking the bedsheets. Now I want to show you the neurovascular structures. Take a look at this structure here. This is the deep branch of the radial nerve which I mentioned earlier. This is the posterior introsius nerve. And if you look carefully, when I'm exerting traction on the main radial nerve here, you will find this will be moving. We can see this is moving. So this is the posterior introsius nerve. Once the deep branch of the radial nerve pierces through the supinator muscle, it becomes known as the posterior introsius nerve. And we can see before it pierces through, it gives this branch here. This is the branch to the extensor carbide radialus longus. This posterior introsius nerve, it continues and it supplies all the muscles on the extensor aspect. And we can see the continuation of the posterior introsius nerve here. And we can see further continuation of the posterior introsius nerve here also. This posterior introsius nerve, it passes through the fourth compartment along with the extensor digitorum tendons. What we cannot see here is that it is also accompanied by the anterior introsius artery which pierces through the introsius membrane and comes here. But in this particular cadaver, it is too small and it is not visible here. So these are the structures that we can see in the various compartments on the dorsal aspect of the hand and the wrist and the forearm. Thank you very much for watching. Dr. Sanjay Sanyal signing out. Mr. Sherwin Weeks is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day. Please like and subscribe.