 Good day everybody. Dr. Sanyal, Professor Department Chair. We are going to focus on the Neurotial region. This is the prone cadaver. So this muscle that we have exposed here, this is the gluteus maximus. And you can see that it is arising in a very extensive way from the coccyx, sacrum, and from the outer surface of the alium, posterior to the posterior gluteal line, and the fibers are then converging here. And this is the heliotipial tract that we can see here. Where the three-fourths of the superficial fibers get inserted, and this aponeurotic expansion goes down and gets attached to the lateral-lateral tubercle of GRD. So what we are going to do now, we have already cut the origin of the gluteus maximus, and we are going to reflect it. And we are going to go straight to the neuromascular structures and their supply. When we reflect it, we see the neuromascular structures. So let's take them one by one. These neuromascular structures that we can see here, this is above the pyriformis. So this is the superior gluteal artery. The superior gluteal artery is a branch from the posterior vision of the internal iliac. And the superior gluteal artery supplies the structures deep to the gluteus maximus, namely the gluteus medius, gluteus minimus, and tensor fascia letter. When I reflect the gluteus medius, what I am doing right now, we can see the rest of the neuromascular structures here. And I have lifted them up here. These are the other branches of the superior gluteal artery, and these are the branches from the superior gluteal nerve. The superior gluteal nerve root value is L5S1. And we can see the superior gluteal nerve is supplying the gluteus medius. And we can see other branches are supplying the gluteus minimus, which is here. And we can see the gluteus minimus from the other side here. And the superior gluteal nerve also supplies the tensor fascia letter, which is located further antrolaterally here. So that brings me to action of these muscles. The gluteus medius and the gluteus minimus, as you can see the fibers are descending vertically down. And they get inserted on the top of the greater trochanter, both the gluteus medius and the gluteus minimus. Therefore, their main action is abduction of the hip and medial rotation. They also help to stabilize the pelvis, especially when we are standing on one leg. It prevents the other side pelvis from sagging down by virtue of their unique insertion. That brings me to a very important clinical correlation here. If there is a deep penetrating injury in the gluteal region and the superior gluteal nerve is injured, then the gluteus medius, gluteus minimus and the TFL will be paralyzed. And that produces a condition known as Trendlenberg sign. What happens in Trendlenberg sign? When the patient is asked to stand on the leg of the paralyzed type, the hip on the other side will sag down because the gluteus medius is not able to stabilize the pelvis. It is called Trendlenberg sign. And because of that, the person will develop one of three gates. One is called the gluteal or the waddling gate or out swinging gate or high-step edge gate. So that is the manifestation of superior gluteal nerve injury from a deep penetrating stab injury. Now let's take the next neurovascular structure. This is again the pyriformis as I mentioned. We can see the pyriformis is coming from the anterior aspect of the sacrum and my fingers is in the greater sciatic notch. The pyriformis emerges from the greater sciatic notch and by means of this narrow tendon, it gets inserted onto the tip of the greater trochanter. Therefore, the pyriformis divides the greater sciatic foramen into a suprapyriformis compartment which I described just now which gives passage to the superior gluteal vessels and the superior gluteal nerve. And it divides the greater sciatic foramen into an infrapyriformis compartment and that is this one here. The portion below the pyriformis is the infrapyriformis compartment. And what are the structures which are emerging through the infrapyriformis compartment? We can see this big nerve here. I'm going from lateral to medial. This is the sciatic nerve. So this is the first structure. The second structure which comes out is this one which I have lifted up collectively. This is the inferior gluteal nerve and the inferior gluteal artery. The inferior gluteal nerve is S1-S2, the posterior division. And this is the inferior gluteal artery which is the branch from the anterior division of internal ligature. The inferior gluteal nerve is the one which supplies the gluteus maximus and the artery also. And we can see the cut portions of the nerve which were entering into the gluteus maximus. This is one cut portion here. This is another cut portion, the vessel. Another cut portion and there are numerous cut portions. So we have to cut them here to reflect the gluteus maximus. What happens when there is an injury of the inferior gluteal nerve? The inferior gluteal nerve injury will produce paralysis of the gluteus maximus. And the action of the gluteus maximus is extension and lateral rotation of the hip. So therefore the patient will not be able to extend and lateral rotate the hip. Additionally, more important function of the gluteus maximus is make the person sit from a standing position and stand from a sitting position or climb or walk uphill. Just imagine when a person is standing and he is about to sit down on a chair, his gluteus maximus is undergoing isotonic eccentric contraction which is also referred to as control relaxation. And likewise from a sitting position when he is standing, his gluteus maximus is undergoing concentric isotonic contraction to enable him to stand. So all these functions will be lost when inferior gluteal nerve is injured. In this connection I can mention there is a condition called epiconus syndrome where there is a legion of the spinal cord just above the conus, that means just above S3. And in epiconus syndrome which can be due to a tumor, patient has very similar findings as gluteus maximus paralysis. Namely, he has severe inability to extend and laterally rotate the hip. So that is with respect to injury to the inferior gluteal nerve. Next you can see here as I mentioned is the sciatic nerve. So let's take a quick look at the formation of the sciatic nerve. Sciatic nerve is formed inside the pelvis by a combination of the lumbar plexus and the sacral plexus. The component from the lumbar plexus is L45 which comes through the lumbosacral trunk. The sacral plexus S123 so that is the root value of the sciatic nerve. In the pelvis it has got two components, a pre-axial division and a post-axial division. And here it is also met by what is known as the posterior femoral cutaneous nerve which we cannot see very clearly here. And as the sciatic nerve emerges from the infrabidiformis compartment, the posterior femoral cutaneous nerve separates off and it supplies the skin of the back of the thigh and also the inferior gluteal region. The rest of the sciatic nerve then descends down on this bed. This bed is composed of the following four muscles. One muscle we can see here, this is the superior gemulus. The next muscle we can see here, this is the operator internus. The next muscle that we see here is the inferior gemulus. And the last muscle is the quadratus femoris. So this forms a bed for the sciatic nerve to pass through and it passes roughly midway between the greater trochanter and the ischial tuberosity. And this is an important landmark. If you want to keep sciatic nerve blocked, we follow the portion midway between these two bony prominences. Likewise, when a person who is jogging for many years, friction of the sciatic nerve against the ischial tuberosity can produce sciatica. This sciatic nerve can be compressed under the piriformis. In about 12% of cases, one of the divisions of the sciatic nerve can go through the piriformis and in 0.5% of cases, one of the divisions, the common fibular division can come even above the piriformis. These are the conditions when the piriformis is especially prone to compression or entrapment and this is referred to as the piriformis syndrome. This typically occurs in skiers when they fall on their buttocks and there is swelling and inflammation which compresses the sciatic nerve. And that can produce symptoms very similar to sciatica in terms of shooting pain down the back of the leg. The sciatic nerve can also be enjoyed in posterior dislocation of the hip. And after these muscles, the sciatic nerve then enters into the thigh and we shall see the course of the sciatic nerve when we come to the thigh. And we can see the sciatic nerve running on the back of the thigh. The sciatic nerve is the one which supplies everything on the back of the thigh, back of the knee, back of the foot, leg, right up to the sole of the foot. This is a photomicograph of a distal stump of a ninja sciatic nerve showing axon regeneration. That brings me to yet another neurovascular structure which I am going to just show but I am not going to mention the details. And that is this here. I have lifted up a composite neurovascular structure here. This is the pudendal nerve and the internal pudendal artery. This complex, it comes out from the greatest sciatic foramen below the piriformis. It winds around this pony prominence which I can feel here and you can see a little bit here. This is the ischial spine and then it goes back through this space. This is the lesser sciatic foramen and it enters into the ischial anal fossa and it runs in the canal called the pudendal canal or the alcox canal and supplies the structures in the perineum. So therefore, to summarize, going from natural to medial, we have S sciatic nerve, G gluteal, inferior gluteal nerve and artery and P pudendal, internal pudendal artery and pudendal nerve. And just to complete the story, let me mention quickly the nerve supply of these deep muscles. The piriformis is supplied by the nerve to piriformis, which is from the anterior ramai of S1, S2. Submeria gemilis and the upper tritinternus is supplied by the nerve to upper tritinternus, which is L5, S1. And the inferior gemilis and quadratus femoris is supplied by the nerve to quadratus femoris, which is also from L5, S1. The action of all these deep muscles is lateral rotation of the hip. So if any of these nerves are injured, which is not very common, then there will be weakness of lateral rotation. And that brings me to the final point. When do we use medial rotation and lateral rotation of the hip? On a day-to-day basis, when we are just walking with each step that we take, our hip rotates medially and the opposite hip rotates laterally and vice versa. So therefore, lateral and medial rotation of the hip is an unconscious thing which we do not do consciously, but it automatically happens each time we walk. So these are all the points which I want to mention about the neuro-vascular structures in the supply in the gluteal region. Thank you very much for watching Dr. Sanyo Sanyo. Sanyo please like and subscribe if you have any questions or comments. Please put them in the comment section below. Have a nice day.