 Good day everybody. Dr. Sanjeev Sanyal, Professor, Department Chair. This is going to be a demonstration of the extensors of the wrist at the torsum of the hand. So this is a supine caregiver. The right hand is pronated. I'm narrating from the right side. Camera person is also on the right side. This structure that we see in front of us, this is the extensor retinaculum of the wrist. The extensor retinaculum is the thickening of the anti-breakable fascia. It extends from the anterior surface of the lower end of the radius and it goes obliquely and medially and it gets inserted not to the ulna but it gets inserted onto the pisiform and the trichotrial bone. If this extensor retinaculum were to be inserted onto the ulna then it would not have allowed pronation and supination. As it crosses over it creates six tunnels under which the various extensors of the wrist pass by. Between tunnel number two and three it gets attached to this tubercle on the torsum of the radius and that is referred to as the torsum tubercle of radius. So let's take a look at the tendons which are passing through each tunnel. This is the first group of tendons that are passing. This is the abductor policies longus and we can see the other end of the muscle here. Abductor policies longus and after that this is the extensor policies braves. This passes through tunnel number one and each of these tendons are enclosed with their own synovir sheets. Then we have the next tunnel. Tunnel number two, these two tendons. This is the extensor carbide radialist longus getting attached to the base of the second metacarpal and the extensor carbide radialist braves which gets attached to the base of the third metacarpal. Then we have tunnel number three. Just to remind you this is the torsum tubercle of radius. Passing through tunnel number three we have the extensor policies longus. We can see that it gets inserted onto the base of the terminal phalanx of the gum. Then we have the fourth tunnel. This gives passage to many structures and I have lifted up all of them here. This is the combined tendon of the extensor digitorum. So this is the digitorum tendon to the index finger and we can see when I exert traction here it moves here. Then this is the extensor to the middle finger. Then we have this is the extensor to the ring finger and this is the extensor to the little finger and we can see it moving here. Along with this extensor digitorum we have one more tendon and that is this one here which is running onto the extensor digitorum tendon to the index finger but on its ulnar side and that is this tendon here and the muscle is located under the extensor digitorum and we can see it moving here. This is the extensor indices. So the extensor indices runs on the ulnar side of the extensor digitorum to the index finger. In the same tunnel we also have these neurovascular structures. We have the posterior interosseous nerve which I have lifted up here which is the continuation of the deep branch of the radial nerve and it also contains the anterior interosseous artery. The anterior interosseous artery actually was running in the anterior interosseous compartment and it then pierces through and runs in the posterior compartment. Now let's come to tunnel number 5. We have the extensor digiti minimi and this is the tendon of the extensor digiti minimi. And we can see that the extensor digiti minimi also runs along with the tendon of the extensor digitorum with the little finger on its ulnar side. And then we have tunnel number 6 and that is this tendon here. This is extensor carpi ulnaris and the other end of the tendon is located here. So these are the 6 tunnels. At this juncture let me mention a few clinical correlations. This space that we have created here, this is the anatomical snuff box. The anatomical snuff box is bounded laterally by the abductor polisus longus and the extensor polisus brevis. Immediately it is bounded by the extensor polisus longus. Approximately it is bounded by the styloid process of the radius, scaphoid bone, trapezium and the base of the first metacarpal. So this depression is known as the anatomical snuff box. This is bridged over by the fascia of the forearm and the content of this triangle is this important structure which I have lifted up here. This is the radial artery. The radial artery runs here under cover of the brachioradialis and then it goes through the anatomical snuff box and we can see it is continuing. And then it pierces the first dorsal introscious muscle and comes to the palm as the deep palmar arch. The other content of the anatomical snuff box is this nerve here. This continues and it runs on the superficial fascia. This is the superficial branch of the radial nerve which also runs under the brachioradialis and it supplies the skin of the dorsal of the palm. In earlier days, Washer women went there to wring clothes. They used to get aseptic tendinitis of these tendons and that is referred to as Washer women's hand or decurbance, stenosing, tino cyanobitis. Nowadays, of course, Washer women don't do such things. Therefore nowadays it is referred to as texting hand or the blackberry hand because people are using these tendons while they are texting continuously or they are using their smart phones. Extensor carpyradialis longus and extensor carpyradialis grievous, especially, can develop cystic degeneration of the synovial sheath because as I mentioned, all these tendons have their own synovial sheath inside their respective tunnels and that cystic mixometer cystic degeneration is referred to as a ganglion. And these ganglion surgically are very difficult to treat even if they are excised, they tend to ricker. Let's take a look at the neurovascular structures that we can see supplying the muscles of the extensor compartment. So for that I'm going to come a little proximally and this is the radial nerve which I had mentioned a little while earlier. The radial nerve comes in front of the common extensor origin that is the lateral epicondyle. The lateral epicondyle is referred to as a common extensor origin where my finger is located because it gives origin to all the extensor muscles. Just in front of the lateral epicondyle that the radial nerve it divides into a superficial and a deep branch. This is the superficial branch which runs as I mentioned under the bricure radialis and the deep branch is the muscular branch. This supplies initially the extensor carpyradialis longus and the extensor carpyradialis grievous which are the two most important extensors of the wrist. These are the two muscles which I mentioned and after that it pierces through the supinator and it comes onto the extensor aspect and we can see it continuing here and it supplies all the muscles of the extensor compartment. And the continuation of this nerve we saw a little while back which passes deep to the fourth tunnel and this is the continuation of the radial nerve here. And if the radial nerve is injured here like for example dislocation of the elbow or fracture dislocation of the proximal radialis joint then it can cause paralysis of the extensors of the wrist especially and that will lead to a very serious condition known as wrist drop. Now let's take a look at the structures on the dorsal of the finger. We have opened up the middle finger dorsal aspect and the same structure will be present in all other fingers. So we can see that on the dorsal of the finger there is an expansion here which I have lifted up on one side and this is the other side of that expansion. This is known as the dorsal digital expansion or the dorsal aponeurosis of the digits. If you notice, sides of the expansions are thickened. The long extensor tendon it gets attached to this and then on the sides the thickened portion gives attachment to the lumbarical muscles and to the entraceous muscles on either side. And after that the aponeurosis then continues and in this region it breaks up into three slips. A medial slip which gets attached to the base of the middle phalanx and the two lateral slips. This is one of that and this is the other one. These two go on either side of the digit and then they unite and they get inserted onto the base of the distal phalanx. So this is the dorsal digital expansion. To summarize this dorsal digital expansion contains the main extensor tendon, it contains the lumbaricals, it contains the insertion of the entraceous muscles. Approximately it is held onto the finger by means of an aponeurotic hood. It is because of this unique arrangement of this dorsal expansion that these entraceous and the lumbarical muscles together can perform what is known as the Z-Movement as shown by my hand here. The Z-Movement is flexion of the metacarpophalangeal joints and extension of the intrafalangeal joints. This movement is possible by virtue of this unique dorsal digital expansion of the digits. This same arrangement will apply in all the digits. In this correction we can mention a few clinical correlations in baseball players or in housewives or those who are arranging the bedsheets. If the finger is held stiff and it gets hit against hard surface the distal phalanx can forcibly flex and it can produce tear of this expansion on the base of the distal phalanx in which case the distal phalanx will become flexed and that is referred to as mallet finger. The next thing is if there is paralysis of the aller nerve which supplies the intrinsic muscles of the head namely the introspecial muscles and the lumbaricals then the Z-Movement will not be possible and therefore the opposite movement will take place and this is referred to as the claw hand. So the basis of the Z-Movement and its opposite that is the claw hand are because of this extensor expansion. So these are some of the points which I want to mention pertaining to the structures on the extensor aspect and the dorsum of the wrist. Thank you very much for watching. Dr. Sanjay Sanyal signing out. If you have any questions or comments please put them in the comment section below. David O is the camera person. Have a nice day.