 Dr. Sajju Sanyal, Professor of Department Chair. This is a third part of a dissection of the head. So just to bring up the speed, this is the flexor etnagulum that we see in front of us. And I have retracted the superficial pommel arch which came from the ulnar artery here to show you the flexor etnagulum in more detail. And we can see immediately it is attached to the PC-Pompon and to the hook of Hammett. Laterally, it is attached to the tuberculum of the scaphoid and the tuberculum of the trapezium. And this flexor etnagulum bridges over the carpal tunnel. We have already split open the flexor etnagulum and that's what I'm doing now. And we can see the cut margin here. We can see the cut margin is very thick. Flexor etnagulum is a very tough structure. And once we split it open, we see the carpal tunnel with the contents passing through the carpal tunnel. So what are the contents of the carpal tunnel? We have these four tendons. These are the tendons of the flexor digital superficialis which I have eviscerated out of the carpal tunnel. And under that we have these four tendons of the flexor digital and profundus which also we have eviscerated out. Apart from these eight tendons, we also have this tendon. This is the flexor policies longest tendon. So these are the nine tendons of the carpal tunnel. Last but definitely not the least, the most important content of the carpal tunnel is the median nerve. This is the median nerve. This median nerve is the one which is responsible for all the carpal tunnel syndrome that we hear about. This median nerve can get compressed in the carpal tunnel because the carpal tunnel is already over-traveled with nine tendons with their sign of its sheets. And compression of the median nerve is how the carpal tunnel produces the carpal tunnel syndrome. So let's mention a few quick words about these tendons. If we were to pick up these four tendons of the flexor digital superficialis and we trace them, we find that this is the tendon which is going to the little finger, this is the tendon going to the ring finger, this to the middle finger and this to the index finger. And under that, we have this flexor digital profundus which are also going to the same four fingers. We will trace the tendons right up to the digits and we can see them here. We find the tendons first run in a fibrous flexor sheath which we have split open. And if you look closely, we see that the superficialis tendon splits into two parts. And through the split portion, the profundus tendon is passing. Same thing we will see in this finger also. We can see the superficialis tendon has split into two parts and through the split portion that profundus is passing. The same thing is seen here also and the same thing is seen here also. The superficialis tendon gets inserted onto the base of the middle phalanx and the profundus tendon gets inserted onto the tip of the cell phalanx. So therefore the superficialis is responsible for flexing the proximal interphalangeal joint. The profundus tendon is responsible for flexing the distal interphalangeal joint. All of them are enclosed in the synovial sheath. The synovial sheath of the little finger is continuous with the synovial sheath of all these combined eight tendons while the synovial sheath of the ring, middle and the index finger stop here. This is referred to as the ulnar bursa. If a person gets an infected thorn prick in the little finger, the infection can spread all the way up to here and can involve this portion of the bursa. And that infection is referred to as suppurative tinocynovitis. Of course, the same thing can happen to these other fingers also, but the infection will stop here because these do not communicate with the ulnar bursa. Now let's take a look at this flexor polises longus tendon. This is the flexor polises longus tendon which is also a content of the carpal tunnel. This flexor polises longus tendon has got its own synovial sheath. And this synovial sheath is referred to as the radial bursa. And infection of the thumb of the synovial sheath will produce radial suppurative tinocynovitis. When these superficialis and the profundus tendons are passing through to the digits, they pass through a fibrous flexor sheath which we have split open here. And that fibrous flexor sheath can sometimes become very tight. And in which case, they can compress and prevent free movement of the tendon here, even though the tendons are enclosed in their synovial sheath. In such a situation, what will happen is the person, if he flexes his finger, after that he has difficulty extending his finger. That's because the fibrous flexor sheath has gripped the tendons tightly and it's preventing full release of the tendon. And that condition is referred to as trigger finger. Now let's take a look at these muscles that we can see here in this dissection. We can see one muscle, small, warm like thin muscle going to the radial side, a second one going to the radial side. Then we have a third muscle here and we have a fourth muscle here. These are the lumbarical muscles. The lateral two lumbaricals, they arise from the profundus tendon to the second and the third digit. And they are unipenate and they get inserted onto the radial side of the dorsal extensor expansion. The medial two lumbaricals are bipenate. And they get inserted onto the dorsal expansion of the ring and the little finger respectively. The lumbaricals is to perform the Z movement, namely flexion of the metacarpophalanges joint and extension of the IP joints. The lateral two lumbaricals are supplied by the same nerve which supplies the lateral half of the profundus, namely the medial nerve. The medial two lumbaricals are supplied by the same nerve which supplies the medial half of the profundus that is the ulnar nerve. This is the ulnar nerve which I have lifted up here accompanied by the ulnar artery. It is passing through a canal here. This is referred to as the guion canal. And the ulnar nerve can get compressed in the guion canal. Or it can also be injured in fracture of the hook of hamate here. Or it can be injured in a condition known as handle bar neuropathy. Ulnar nerve gives a communicating branch to the medial nerve. It gives a superficial branch which we can see going to this little finger and the medial part of the ring finger. And it gives a deep branch which supplies all the intrinsic muscles of the hand except the lateral two lumbaricals. So injury to the ulnar nerve here will produce paralysis of the hypothera muscles. And it will also produce paralysis of the medial two lumbaricals. And the person will get what is known as ulnar claw hand. Now let us come to the medial nerve, which I mentioned to you in the beginning. This is the medial nerve. The medial nerve, it passes through the carpal tunnel. And we can see it is giving rise to these branches in the palm. It is giving a branch to the radial side of the ring finger. It is giving a branch to the entire middle finger. It is giving a branch to the entire index finger. It's giving a branch to the thumb. These are all the branches of the medial nerve. And I have picked up the whole stem of the medial nerve here. Additionally, we can see this is a communicating branch from the medial nerve to the ulnar nerve. And finally, we can also see this branch of the medial nerve. This is called the recurrent branch of the medial nerve, which supplies the thinner muscles. This is a very superficial branch. And this can be injured if a person gets a superficial laceration of the palm here. If a person falls on his palm and it strikes a sharp object, in which case, the person can get paralysis of the thinner muscles if this nerve is injured. This medial nerve is the main culprit, which is compressed in the carpal tunnel syndrome, in which case, the person will have tingling, numbness, and peristhesia of this half of the ring finger, middle finger, index finger, and the thumb. Additionally, the person will have weakness of the thinner muscles and weakness of the lateral duolembricals, because they are also supplied by the medial nerve. In this connection, I need to mention that the branch of the medial nerve, which supplies the palmar skin, the lateral three-fourths of the palmar skin, does not arise from the carpal tunnel. It arises from a branch of the medial nerve, which goes above the carpal tunnel. So therefore, in carpal tunnel syndrome, the palmar skin is spared. So this is the important clinical significance of the medial nerve. That brings me to the point which I had started with in the dissection when we made an incision of the flexor retinaculum to relieve a pressure of the carpal tunnel. This incision that I made is the exact incision that is done in surgical practice. Earlier days, we used to do it by means of an open surgery. Nowadays, this incision in carpal tunnel syndrome is done by means of an endoscope. In either situation, if you notice, I have made the incision slightly towards the ulnar side. The purpose of doing this incision is to safeguard three structures. Number one, we have to safeguard the recurrent branch of the medial nerve. Otherwise, if we got this, then we can produce paralysis of the theramoses. The second structure to be safeguarded is the communication between the ulnar nerve and the medial nerve. And the third structure to be safeguarded is this one, which is the superficial pavar arch, which is coming from the ulnar arch. So these are the three structures that we need to safeguard when we are doing a release of the carpal tunnel in carpal tunnel syndrome by cutting open the flexor retinacula. Now what I have done, I have lifted up the superficialis and the profundus tendons. And my finger has got under all of these tendons. And you can see my finger here. This space where my finger is located now, this is called mid pavar space. This mid pavar space is a space under the profundus tendons. Just to bring up the speed, covering all of this was the pavar eponeurosis. We have removed that. Just under the pavar eponeurosis was the superficial pavar arch, which we have reflected to one side. These long tendons, they are in the central compartment with the corresponding numericals. And under that, this space where my finger now is located, this is called the mid pavar space. If a patient sustains an infection of the mid pavar space, and you can see it is quite a big space, the infection can track down. It can track through the carpal tunnel, as you can see here. And it can come into this space on the flexor aspect of the wrist. This is called the space of parona. So therefore, the space of parona is bounded by, anteriorly by the flexor digital profundus tendon muscles. Firstarily, it is bounded by this muscle here, which is called the pronated quadratus. Medially, it is bounded by the attachment of the anti-brickle fascia to the radius. And laterally, it is attached to the anti-brickle fascia to the radius. And approximately, it is bounded by the attachment of the flexors of the palm to the radius. So this whole thing is called the space of parona, which communicates with the mid pavar space. Additionally, we have another space in the palm. And then also we can see here, these are the tina muscles, as I mentioned. This is in the compartment called the tina compartment. And this is the adductor policies muscle, which is in a separate compartment called the adductor compartment. Between the tina muscles and the adductor compartment, this space that we see here, this is called the tina space. So this is also a potential space of infection. And these are the two spaces that we can see in the palm. And finally, to conclude, we have a hypotenal compartment, a tina compartment, an adductor compartment, a central compartment. And dorsal to the mid pavar space, we have the interosseous compartment. So these are the various compartments, each of which contain the various muscles. So these are the structures, which I wanted to show you in the deep dissection of the hand. Thank you very much for watching, Dr. Sanjay Sanyal, signing out from MD1 students, their assistant. David, who is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day.