 Good day everybody. Dr. Sanjay Sanyal, Professor Department Chair. So this is going to be a demonstration of the left axilla and we were going to focus on the posterior cord of the brachial plexus and the radial nerve and the axillary nerve and the branches of the posterior cord. This is a supine cadaver. This is the left side. I'm standing on the left side and the camera person is also on the left side. Just to bring you up to speed, this muscle that we see here, this is the latsomus dorsi on the left side. This muscle that we see, this is the T-rease major and this muscle that we see here, this is the subscapularis on the left side. This is the coracobrachialis. This is the biceps brachii and we have reflected the pectoralis minor and the pectoralis major to expose the axilla. This is the axillary vein and it is thrombosed here and this is the axillary artery. Now, if I retract the axillary artery, we can see this is the posterior cord of the brachial plexus and as we know, it's called the posterior cord because it is located behind the axillary artery. The posterior cord in the axilla, we can see only the cords and the terminal branches of the brachial plexus because the roots and the trunks are in the neck which we cannot see in this dissection and the divisions are in the cervical axillary canal which is deep inside which also we cannot see so therefore we can see only the posterior cord. We know that the posterior cord is formed by the union of all the posterior divisions and therefore it is the largest cord and this is the posterior cord which I have lifted up here. This is the posterior cord. So, let's trace the first terminal branch of the posterior cord and that is this one here which I have lifted up. This is the axillary nerve. The axillary nerve goes laterally. It goes through the quadrangular space and we can see that it is accompanied by these viscular structures here. This is the posterior circumflex-humeral artery and the posterior circumflex-humeral vein coming from the axillary artery. So, this axillary nerve, it winds around the surgical neck of the humerus. It goes through the quadrangular space. So, what is the boundary of the quadrangular space? Superiorly, it is bounded by the Td's minor, the head of the humerus and it's bounded by the subscapularis. Inferiorly, it is bounded by the Td's major. Laterally, it is bounded by the surgical neck of humerus and medially, it is bounded by the long head of the triceps. So, this quadrangular space is the one which gives passage to this axillary nerve, the posterior circumflex-humeral artery and the posterior circumflex-humeral vein and we can see that here. Here, the axillary nerve can be injured in two different ways. If there is a fracture of the surgical neck of humerus, then the axillary nerve can be injured and if there is an inferior dislocation of the shoulder joint, then also the axillary nerve can be injured. This is an x-ray of the right shoulder to fracture the surgical neck of humerus in a patient. Injured to the axillary nerve will produce the maximum disability in terms of paralysis of the deltoid muscle. The deltoid is supplied from the inner aspect by the axillary nerve here. We can see that here. And that will lead to inability to extend the shoulder joint. It will also lead to paralysis of the Td's minor, but that is not of much clinical significance. And additionally, there will be a loss of sensation in the upper lateral aspect of the arm because the axillary nerve also supplies the arm. So that is about the axillary nerve which is arising from the posterior cord, the brachial plexus, the first terminal branch and we can see that here. Now let's trace the rest of the posterior cord. The rest of the posterior cord continues down and we can see that it's continuing down here, this one. This is the radial nerve. This is the largest branch from the posterior cord and it goes behind and we can see it is disappearing again somewhere here and we can see that here. This is the radial nerve and we can see it is accompanied by these vascular structures. These are the profunda brachii artery and the profunda brachii vein which come from respectively from the brachial artery and the venae comitantes of the brachial vein. Actually we can see them from behind more clearly and that region is referred to as the triangular interval. They do not pass through the triangular interval but they pass in relation to the triangular interval. That's why it is called interval. This triangular interval is bounded superiorly by the Td's major. It is bounded laterally by the lateral head of the triceps and it's bounded medially by the long head of the triceps. And after that it goes behind the humerus in a groove called the spiral groove or the radial groove. This spiral groove or the radial groove is the groove between the lateral head and the medial head of the triceps and the triceps is located where my finger is pointing here. Before it enters the lateral radial groove it gives a branch and we can see that branch here. It gives a branch to the long head and it gives a branch to the medial head of the triceps. And in the radial groove it gives a branch to the lateral head of the triceps. Here also the radial nerve can be injured whether there is a fracture of the shaft of the humerus. And in such a case the long and the medial head will be spared because the branch has already come off but the lateral head will be paralyzed. But that will not produce any significant disability in terms of extension of the elbow because the lateral head is used only for powerful extension. The workhorse extensor of the elbow is the medial head which will be spared. And therefore after this we cannot see the radial nerve. Now we have come in the cubital fossa and we can see this is the radial nerve which I have picked up here. That means the radial nerve went through the spiral groove like this. It went behind this arm and it came in front of the lateral epicondyle and here I can feel the lateral epicondyle with my finger. And it is located in front of the lateral epicondyle in the cubital fossa under cover of this muscle here. This is the brachial radialis. So therefore this is the lateral most content of the cubital fossa and this is the cubital fossa. The other contents of the cubital fossa are the medial nerve, the brachial artery, tendon of the biceps and the lateral most is the radial nerve. The radial nerve here is likely to be injured in dislocation of the proximal radial nerve joint which is not very uncommon in children especially if we try to lift them up by holding the hand. It can also be injured in adults when there is a montegia fracture where there is unnerved fracture and proximal radial nerve joint dislocation. This is an x-ray to show montegia fracture dislocation. So that is when the radial nerve can be injured here. If the radial nerve is injured here then it will lead to wrist drop. Let us see how the radial nerve is distributed here. In front of the lateral epicondyle under cover of the brachial radialis the radial nerve divides into a superficial division and a deep division. And let's take a look at the superficial division. This is the superficial division. I have lifted it up here. This is a cutaneous branch of the radial nerve and you can see this runs under cover of the brachial radialis here and it goes all the way under cover of the brachial radialis. It does not supply any structure as the other part of the superficial branch. We can see it here. It comes out from under cover and it runs on the surface of the anatomical snuff box. On the roof of the anatomical snuff box and then it supplies the skin on the major part of the dorsum of the head. So this is the cutaneous distribution of the superficial branch of the radial nerve. Now let's take a look at the deep branch. The rest of the radial nerve is the deep branch. Immediately we can see it is giving some branches to the muscles on the extensor aspect. It supplies the extensor carbide radialis longus. Extensor carbide radialis brevis and extensor carbide allaris. And thereafter it pierces through the supinator muscle which forms the flow of the cubital fossa. And thereafter it becomes known as the posterior interosseous nerve. And as the posterior interosseous nerve, the radial nerve supplies all the nerve muscles from the extensor aspect of the arm. Injury to the radial nerve will produce a very serious disability and that is called wrist drop. As shown by my hand here, the person will be unable to dorsiflex his wrist. And it is such a serious disability that there are many instruments which have been created. One of them being the nest instrument which is used to stimulate the extensor muscles in order to produce wrist elevation. This is a picture of the functional electrical stimulation which is used to stimulate paralyzed hand muscles. And it is showing the stimulation of the extensor muscle of the hand. So this is the full course in distribution of the radial nerve with its clinical significance. Now let's take a look at some of the three other branches of the posterior cord of the brachial plexus. Having described the radial nerve and the axillary nerve, let's come back to the posterior cord. So we have come back to the posterior cord and I have lifted it up. This is the posterior cord of the brachial plexus. I have retracted the axillary artery and the axillary vein. We can see three other branches. Let's take the most important, the longest branch here. This is the one which I have picked up here. This is the thoracodorsal nerve. The thoracodorsal nerve as you can see it is coming from the posterior cord and it is supplying the latsimus dorsi muscle. This nerve can be endured when we are doing axillary dissection for after breast cancer surgery. And if there is an injury then the latsimus dorsi muscle will be paralyzed and the person will not be able to climb and the person will not be able to use a crutch. This is one branch. Now let's come back again. Just below the thoracodorsal we can see yet another branch here which I have lifted up. This is the lower subscapular nerve and we can see it is supplying the t-rease major and it also supplies the subscapularis. And if we go further up we can see yet one more branch and I am going to retract this to show the other branch and I have lifted it up here. This branch. This is the upper subscapular and we can see that it is supplying the subscapularis muscle. So this is the upper subscapular supplying the subscapularis, the thoracodorsal supplying the latsimus dorsi and the lower subscapular which supplies the t-rease major as well as the subscapularis. So these are the other branches of the brachial plexus. These nerves can be endured when we are doing an axillary dissection for breast cancer and therefore we have to take precaution to safeguard it. At this point I can mention that while we are doing an axillary dissection for breast cancer the axillary nerve itself is not so commonly endured because it is located high up and it goes out through the quadrangular space. The nerves which are most likely to be endured are these and it is also likely to endure this nerve which is not a part of the posterior cord. This is the long thoracic nerve of Bell which comes from the roots of C567. So these are the points which I wanted to mention to you about the posterior cord, the radial nerve, the axillary nerve and other branches of the posterior cord. Thank you very much for watching. Dr. Sanjeev Sanyal signing out. Mr. Kendal Kumberbatch is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day. Stay tuned for other nerves in the axillary axilla.