Origins, insertions, innervation and functions of the gluteal muscles.
Hello, everyone! This is Joao from Kenhub, and welcome to another tutorial where, this time, I'm going to be talking about the gluteal muscles that we’re going to be looking at right now on your screen. And these are muscles that you find on your buttocks region. And on this tutorial, I will help you learn and understand the anatomy and functions of the gluteal muscles.
Now, before we move forward, I want to just describe a little bit of what you’re seeing here on your image. We’re looking at the posterior or dorsal view of the bony pelvis, right here. And you can see the group of muscles that we’re going to be discussing on this tutorial, right about here. And these are the right gluteal muscles. You would, of course, have the same here on the left side. And you can see a little bit of the femur here projected here inferiorly on the image here.
Now, keep in mind that now I'm going to be adding another set of muscles known as the posterior thigh muscles. So you can also see, if I zoom out, you can then see the gluteal muscles in context with other muscles of the lower limb.
Now, on this tutorial, I want to add that the gluteal muscles are important because they’re essential for different functions including extension and also abduction of the hip joint. And therefore, they’re quite useful for different things, including walking, standing on one leg, or just walking the stairs.
Now, the gluteal muscle group contains four muscles and these are the gluteus maximus, the gluteus medius, the gluteus minimus, and the tensor fasciae latae. Underneath the gluteal muscles, we’re going to find another layer known as the posterior hip musculature that we’re going to be discussing on this tutorial, and you can see now on the image on the right side. And these include the piriformis muscle, the internal and external obturator muscles, the superior and inferior gemelli, and the quadratus femoris.
Now, let’s start with the very first muscle here on our list, seen here highlighted in green. This is, yes, the greatest of all gluteal muscles. For that reason, we had to call it the gluteus maximus. Now, the gluteus maximus shapes the superficial gluteal surface and is the strongest extensor and also the external rotator of the hip joint.
Now, in terms of origin points, we need to remember a few, including the sacrum which will serve as an origin point. And you can see here that the gluteus maximus is arising from the dorsal part of the sacrum. The ilium will also serve as an origin point, specifically the gluteal fossa. A ligament will also serve as an origin point known as the sacrotuberous ligament. And we can also consider the thoracolumbar fascia as an origin point for this muscle.
Now, let’s take a look at the insertion points for the gluteus maximus. And for the caudal fibers, they will insert at the gluteal tuberosity of the femur. While the cranial fibers go over into insert on what is known to be as the iliotibial fascia, iliotibial tract on the fascia lata. You can see a piece here of the gluteal muscle that will be connecting to the iliotibial tract. Now, keep in mind that the iliotibial tract is a strong fibrous bend on the outside of the thigh inserting at the lateral condyle of the tibia.
Let’s take a look now at the functions of the gluteus maximus. And this includes the most important ones which are the extension of the thigh, as you can see here, and also external rotation of the hip joint, as you can see with the arrows, and also, we need to include that this muscle is going to help on stabilizing the hip joint. Important to add here that the contractions of the cranial fibers will abduct, and the caudal fibers, when they contract, they will adduct the femur. The explanation for this opposite or this opposite movement of the cranial and also caudal fibers is that the cranial fibers are positioned above the rotational pivot point of the joint. Thus, a contraction causes abduction. And the caudal fibers run below the rotational axis, so then, will cause adduction.
We’ve learned almost everything about the gluteus maximus, but there is still the innervation missing. And here we find the nerve highlighted in green that is going to be innervating the gluteus maximus. This is known as the inferior gluteal nerve, and you have here, also, the Latin terminology. And coming out… or this nerve will come out of the sacral plexus.
Now, let’s continue on to the next muscle on our list. This is known as the gluteus medius. And this is positioned one layer underneath the gluteus maximus. In terms of origin point for the gluteus medius is going to be the iliac wing or the gluteal fossa. The gluteus… The gluteus medius muscle originates between the anterior and also the posterior gluteal lines of the ilium.
Let’s look at the insertion point that you can clearly see on this image here on the right side. The insertion point for the gluteus medius is going to be the greater trochanter of the femur right about here as you can see. This is the insertion point for this muscle.
Now, let’s look into the functions of this muscle. And this… The main ones that you need to remember and write down on your notes are going to be abduction and also internal rotation of the hip joint. And keep in mind that the anterior part of the anterior fibers of this muscle is going to be causing the internal rotation, while the posterior part or the posterior fibers will be causing extension and external rotation. And also write this down that this is one of the most powerful muscle for abduction and also internal rotation of the hip joint.
Moving on to the small ones, the small gluteal muscle: the gluteus minimus. And the gluteus minimus is found also one or underneath the gluteus medius. And if I show you here the… or add the gluteus medius to the image, you can now see the gluteus minimus just underneath it.
In terms of origin point, we’re going to see that this muscle is going to be coming from the iliac wing or the gluteal fossa. And the gluteus minimus originates a short bit below the gluteus medius between the gluteal lines of the ilium.
In terms of insertion point, we’re going to see the same insertion point as we’ve seen on the medius, and this is going to be the greater trochanter of the femur.
Now, let’s take a quick look at the functions of the gluteus minimus. The first one is also like we’ve seen on the medius. It’s going to be abduction and also internal rotation of the hip joint. Now, in this case as well, we’re going to see that the interior part or the anterior fibers are going to be responsible for internal rotation, while the posterior fibers are going to be responsible for extension and external rotation. Altogether, the medius and the minimus are going to play a major or an important role in stabilizing the pelvis.
Before we move on to other muscles, I want to make here a clinical point related to the medius and the minimus, and to do so, I'm showing here the image of the highlighted medius and the shy minimus just hiding beneath it. Now, what I want to show here with this image is that in order to understand the function of how these muscles are able to stabilize your pelvis, imagine you’re standing on your right leg like you see on the picture. If these small muscles, these gluteal muscles, the medius and the minimus, wouldn’t be there, your pelvis would then be dropped to the left. The muscles hold it towards the right femur and thus erecting the pelvis. If in any case the muscle or its innervation is damaged, what is going to happen, people will have their pelvis dropped down to the healthy side, this is what we call the Trendelenburg sign, or you can also call it the Trendelenburg position.
Next muscle on our list is this one seen here, highlighted in green, known as the tensor fascia latae. This is a thin muscle that lies above all hip muscles and can be easily palpated at the side of the hip, especially in athletes. Origin point, we’re going to look at two. The first one is known as the iliac crest, and the other one is going to be the anterior superior iliac spine, which you can also see here on this image.
Now, it is time for us to move on to the insertion point of the tensor fascia latae, and I mentioned one point because that’s all you need to remember. And this muscle is going to be inserting on this bend here, as you can see, this long bend. This is known as the iliotibial tract. Now, the iliotibial tract is a longitudinal fibrous reinforcement of the fascia lata. Now, well, you may ask what is the fascia lata—is basically a deep fascia surrounding the entire thigh musculature.
It is time for us to move on to the functions associated to the tensor fascia latae. Now, the main task of this muscle is to sustain tension of this bend that we just talked about, the iliotibial tract. As the femoral shaft meets the pelvis, there is going to be an angle pressure from above, which imposes high bending strain to the femur. Both of the hip abductors and the tensor fascia latae counteract the pressure on the opposite side and helps stabilize the bone. This is what we call the tension bending effect. In addition, there are other functions that we need to include here on this list, and these are the abduction, flexion, and also internal rotation of the hip joint.
Now, I covered three muscles, but I did not explain their innervation, but now you’re seeing it highlighted in green. This nerve is responsible for the innervation of the three muscles that we just covered. So the gluteus medius, the gluteus minimus, as well as the tensor fascia latae are all innervated by the superior gluteal nerve which comes out of the sacral plexus.
And as I mentioned earlier, the second part of this tutorial includes the posterior hip musculature. Now, the posterior hip musculature comprises a group of muscles that extend from the pelvic bone to the femur. During their course, they cross the hip joint dorsally. And you can clearly see here on this image the group of muscles that we just talked about going all the way from the pelvis to the femur.
Before we talk about them in a little bit more detail, I just want to start off with the posterior hip musculature in terms of their innervation. And this is going… the innervation is going to be supplied by the direct branches of the sacral plexus with the exception of one muscle of that list, which is the external obturator nerve, which we’re going to look its innervation later on this tutorial. So remember that all posterior hip musculature or muscles are going to be supplied by direct branches of the sacral plexus.
On to the first one on our list, the piriformis muscle. And about the origin of this muscle, this is going to come from the ventral side of the sacral bone also known as the pelvic surface of the sacrum. And as you can see here, this muscle is originating from the front of this or the ventral side of this bone here known as the sacrum.
In terms of insertion point, the muscle runs to then the greater trochanter of the femur as you can see, also, here.
Let’s take a look at the different functions of the piriformis. Now, the piriformis muscle is an external rotator of the hip joint. Another functions related to the muscle include abduction, as you can see here also with the arrows, and slight extension.
The next muscle on our list is going to be these two muscles here, this pair that is known as the internal obturator, seen here on the left side, and the external obturator muscle, seen on the right side. And you can clearly see why we named it internal obturator and external obturator, because as you can see here on the external obturator, it’s found a bit more ventrally while the internal one is found a bit more dorsally.
Now let’s take a closer look at these two muscles. And what you need to know about the internal and external obturator muscles in terms of origin point is that they have a sim… the same one, and that one would be the obturator membrane and its bony margin.
Now, in terms of insertion point, you also need to remember that both of them are going to extend and go all the way to, then, insert at the trochanteric fossa on the femur. Now, if you remember from previous slides, I mentioned that all the muscles from the posterior hip, they’re going to be supplied by direct branches of the sacral plexus, but there was an exception. And this exception is going to be supplied by the nerve that you see here, highlighted in green, which is known as the obturator nerve. Now, if you also remember correctly, the exception is one of the muscles that we’ve been talking about, which is the external obturator muscle.
Now, let’s talk about the different functions associated to the internal and external obturator muscles. Now, in terms of functions, these muscles work as external rotators of the hip joint, as you can see here with these arrows. Now, in addition, the external obturator muscle has or produces adduction or has an adduction role in the hip movement. And the internal obturator is going to have slight extension.
The next set of muscles is also a pair known as the gemelli. Now, as you can see, you have them highlighted in green on both these images. On your left side, you find the superior gemellus muscle. And on the right side, you find the inferior one.
Now, let’s talk about their origin points for both the gemelli. Now, the origin points are the ischial spine. The superior gemellus muscle originates from the ischial spine as you can see here. This is going to serve as the origin point for this muscle. Now, the inferior one is going to come from the tuberosity of the ischium as you can see here coming all the way from the superior portion of the tuberosity of the ischium. And then they both go and insert into the trochanteric fossa, the trochanteric fossa on the femur. And you can clearly see on both of these images that they’re inserting very close to one another.
Now, it is time for us to move on to the functions of the gemelli. And what we see here is that the superior gemelli muscles are going to serve as external rotators of the hip joint, and other functions that these muscles are going to have include adduction and also extension of the hip.
Moving on to the last muscle here on our tutorial, the quadratus femoris, and the quadratus femoris originates at the tuberosity of the ischium as you can clearly see here from this image that this muscle is originating from the tuberosity of this bone.
Now, in terms of insertion points, this muscle is going to cross the border and go all the way to the intertrochanteric crest, as you can see here on the femur. And this area is known as intertrochanteric crest because it exists as an area between the greater trochanter and also the lesser trochanter as you can see here on these images.
Moving on to, then, the functions associated to the quadratus femoris. And what you need to know is that the quadratus femoris muscle is an external rotator of the hip as well as an adductor of the hip joint.
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