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Structures of the thigh and the pelvis at the level of the quadratus femoris muscle.
Meet the hip joint - one of the largest and most important joints of the body. The hip joint is also one of the most mobile and freely movable joints which we use to walk, run, sit, stand, and dance just like our friends here. The hip joint requires a number of muscles to act on it in order to execute such functions. Not only is it so crucial for our locomotion, but the hip joint is what connects our lower limbs to the rest of our body. So, it's an important place that we find a number of nerves and blood vessels.
In our tutorial today, we'll be exploring this region in detail and looking at all of these structures in cross-section at the level of the quadratus femoris muscle.
The quadratus femoris muscle is one of many that acts to stabilize and rotate the hip joint. So, if we draw an imaginary line through this muscle, we end up with a cross-section that looks like this. This cross-sectional image is what we'll be primarily using throughout this tutorial, and while we move through this tutorial, atlas illustrations of each structure we'll look at will also accompany this cadaveric cross-section.
First, we'll look at the bony structures as these will act as bony landmarks to help us identify the muscles and then we'll explore the muscles from the most lateral aspect to the medial aspect before we touch upon the blood vessels and nerves that can be found just here. But before we get into the nitty-gritty, let's quickly review our anatomical planes and the directionality of a cross-section so that we can fully appreciate the spatial relationships that each structure has with the other structures around it.
So, I hope you remember that there are three planes in which the body can be divided. We have the coronal plane, the sagittal plane, and the axial or transverse or cross-sectional plane. The latter of these planes – the transverse plane - splits the body into superior and inferior parts and is very important when we study MRIs, CT scans, and cross-sectional anatomy.
In clinical anatomy, when we view CT or MRI scans and cross-sections of the body, we're viewing the image as if we're staring up from the patient's feet. So, we have the right side of the body over here, the left side over here, the front or anterior side of the body over here, and the back or the posterior side of the body just here.
Now that we're familiar with how we should orient ourselves, let's dive into the cross-sectional anatomy at the quadratus femoris muscle level.
There are two major bones at this level of cross-section that we'll concern ourselves with today and go over in a bit detail in a few moments. The first of these is the femur – the thick thigh bone – and the second bone is the hip bone.
The femur is by far the strongest bone in the body and is also the bone of the thigh. It acts as an insertion point for several muscles originating from the pelvis which we'll see later in this tutorial. In the cross-section to the left, the femur is highlighted in green, and as you can see, it looks quite thick at this point. This is due to the level at which the cross-section is cut.
If we look at this illustration of the femur on the right, we can see that the most proximal portions of the femur here are more expanded than the rest of the bone. The cross-section is made roughly at this point which cuts through the greater trochanter of the femur and which relates to this expanded portion of the femur in the cross-sectional image on the left.
As mentioned before, the hip bone is the other bone that we'll see in the cross-section at the level of the quadratus femoris muscle, and the pelvis is actually made up of two hip bones - one on the left and one on the right. There are two particular structures that we'll see in cross-section and these are the ischium and the pubic symphysis.
The ischium makes up the posterior-inferior portion of the pelvic bone and it's highlighted in green on the illustration on the right. We can see the ischium as the most posterior bony structure in the cross-section at the level of the quadratus femoris muscle and it's highlighted in green in the image on the left. The fibers of the quadratus femoris muscle actually originate from the ischium.
And the last part of the pelvic bone that we can see in this image is the pubic symphysis. The pubic symphysis is a cartilaginous disc that can be found joining the anterior portions of the two halves of the pelvis, and in this cross-section here, it's this tiny little structure which is highlighted in green. If we look at it in this illustration, we can see that the pubic symphysis joins the two pelvic bones anteriorly at the pubis portion of each bone, pointed out here by the arrows on both the illustration and the cross-sectional image.
So now that we've covered the important bones and the associated structures, let's dive into the musculature that can be found at this particular cross-sectional level.
So, let's, begin with the quadratus femoris muscle. Highlighted in green to the left, we can see the quadratus femoris muscle spanning between the ischium just here and the femur which is just here. Looking at the atlas image of the quadratus femoris muscle, you can see the spatial relationship of the muscle traveling between the ischium and the femur.
The largest muscle we'll see in this cross-section is the gluteus maximus muscle, which is a muscle of the dorsal gluteal musculature and the main component of the buttocks. It's also the most superficially situated of the three gluteal muscles – the three gluteal muscles being, of course, the gluteus maximus, the gluteus medius, and the gluteus internus.
Gluteus maximus is seen here highlighted in green in both images and is found as the most superior muscle on the posterior surface of this region. So, just by looking at this cross-section and being able to identify the gluteus maximus muscle, we're also able to orientate ourselves on this image and know which is the anterior and which is the posterior aspect of the patient.
As we move towards the anterior portions of the cross-section, we will run into the gluteus medius muscle, which we mentioned a little bit earlier, and it's interesting to view it in this section as it appears as a smaller portion of muscle near the lateral aspects of the femur and closer to the anterior sides than the posterior side of the image on the left.
The gluteus medius descends inferiorly towards the femur and as it does this, it inserts on the superolateral portion of the femur called the greater trochanter. The greater trochanter can be seen highlighted in green in this image. And the way the gluteus medius travels to find this insertion point is what leads it to appearing primarily lateral in the cross-section to the left.
So now that we know where the gluteus maximus and medius are, it's really easy for us to identify the iliotibial tract. So, this particular structure is highlighted in green between the two muscles in cross-section, and as you can see, it descends down the lateral side of the thigh and the leg as seen in the illustration to the right.
So, the iliotibial tract is composed of connective tissue from several muscles within the thigh and it terminates when it reaches the knee. One such muscle that contributes connective tissue to the iliotibial tract is the tensor fasciae latae muscle. And, on the right, we can see an illustration of the tensor fasciae latae muscle. These fibers have their origin from the lateral aspect of the anterior pelvis. The level of the quadratus femoris muscle – the cross-section – would dissect through the muscular belly of the tensor fasciae latae muscle so we can see it highlighted in green in the anterolateral portions of the cross-sectional image.
As we move along the anterior aspect of this cross-section and make our way medially, we eventually run into the rectus femoris muscle, and this muscle is one of four that make up the quadriceps group of muscles, which you may or may not have heard of before, and this muscle is one of four that make up the quadriceps group of muscles.
The illustration to the right shows us our rectus femoris highlighted in green and it's quite evident that it runs in the anterior compartment of our thigh right down the center. Looking at this in cross-section, we can see it highlighted in green just medial to the tensor fasciae latae muscle and traveling down the center of our anterior thigh.
Just deep to the rectus femoris, we find another member of the quadriceps family – the vastus lateralis muscle. If we take a look to the illustration to the right of the slide, we can see the vastus lateralis traversing down the lateral thigh, hence, its name. In cross-section to the left, we see the same muscle highlighted on the outside or lateral sides of the thigh. Together with the rectus femoris then other members of the quadriceps muscle group, they act to extend the knee as if kicking a soccer ball.
This next muscle is one of the longest muscles in the body and it forms an S-shape over the top of the quadriceps, and this is the sartorius muscle. We can see this characteristic S-shape of the sartorius muscle in the image to the right highlighted in green. And when comparing this muscle to the cross-section to the left, it is understandable that the sartorius muscle is the most anterior muscle as we can see pointed out right here. The sartorius muscle aids in extending the knee and also acts as a hip flexor.
As we move more medially along the anterior part of this cross-section, we eventually run into the iliopsoas muscle, highlighted in green here on the image on the left. The iliopsoas muscle is composed of two muscles that come together to act in flexing the hip joint and these two muscles we can see in the image off to the right – and these are the iliacus and the psoas major. In cross-section at the level of the quadratus femoris muscle, the iliopsoas appears just medial to the vastus lateralis muscle.
So, the muscle that we find next to the iliopsoas in the cross-section is the pectineus muscle. Looking at the image to the right, the pectineus muscle, highlighted in green, is found in the anterior part of the upper inner thigh. Reflecting this onto our cross-section to the left, the pectineus muscle is the most medial large muscular belly that we can see here. This particular muscle aids in adducting or bringing our legs back towards the midline like when we're doing a jumping jack.
So, in this image, what appears in the cross-sectional image to be almost connecting pectineus muscle but is actually not is the pyramidalis muscle. We can see in the illustration to the right how small this muscle is (___9:28 overlapping voices___) in the center of the cross-section to the left highlighted in green. The pyramidalis muscle originates from the pelvis to insert onto a thin band of connective that runs along the center of the abdomen known as the linea alba.
The next two muscles we're going to be talking about are involved in rotation and stabilization of the thigh bone at the hip. So, to understand this muscle, we want to have a look at this illustration just here, and as you can see, the obturator externus muscle which is highlighted in green originates from the superior and inferior pubic rami that surrounds the obturator foramen and the external surface of the obturator membrane. And we're looking at this image posteriorly so the obturator externus is on the anterior aspect of the obturator foramen. When viewed in cross-section, the obturator externus muscle can be seen just anterior to this bony portion of the pelvis which we previously identified as the ischium.
Antagonistic to the obturator externus is the obturator internus muscle. By taking a look at the illustration to the right of the slide, the obturator internus muscle can be found on the internal or posterior aspect of the obturator foramen. And let's just take a look at our cross-sectional image one more time. So, here we have the ischium, and the obturator internus highlighted in green is just posterior to this bony landmark.
The last muscle that we're going to be looking at today is the puborectalis muscle. And this particular muscle is sometimes referred to as the puboanalis muscle as well as the puborectalis sling, as it forms a sling around the rectum, and we can see it here coming from the pubic bones forming a U-shape around the rectum and several other structures.
So, in a male cross-section which is what we have here of the body at the level of the quadratus femoris muscle, we can see the prostate. And the prostate is found anterior to the rectum and it's highlighted here. If we take a look at the atlas illustration to the right, we can clearly see the relationship between the prostate and the rectum. The prostate is the bulb-like structure highlighted in green and we see it anterior to the rectum, and the other structure that is closely related to the prostate is the urethra, which is the structure through which urine is carried from the urinary bladder as well as semen from the testes.
In men, the urethra travels right through the center of the prostate and we can see the urethra highlighted here in a cross-section, and it can also be seen highlighted in green n the atlas image on the right.
Alright, so that takes us to the end of our little section on muscles and some of the associated structures found within the cross-section at this level. Let's move on now to talk about three blood vessels and two nerves that we can see in this cross-section.
So, we're going to begin by talking about blood vessels and the first blood vessel that we're going to be looking at is the femoral artery. So, the femoral artery supplies the lower limb with oxygenated blood and we can see this highlighted in green in the image on the right. And this particular artery lies on top of the pectineus muscle pointed out just here and when we look at the cross-section to the left, we can see the femoral artery anterior to the pectineus muscle.
The femoral artery also sends a posterior branch to supply the posterior compartment and the deep muscles of the thigh with oxygen-rich blood and this branch is the deep femoral artery, and we can see it highlighted in green in both of these images. In our cross-section to the left, we can see that the deep femoral artery is located more lateral and adjacent to the femoral vein at this level.
The femoral vein is the largest of the blood vessels that we'll find at this particular level, and since veins lack muscular walls, the femoral vein can appear to have an irregular shape. And of the two femoral vessels that we find in this area, the femoral vein is the medial femoral blood vessel that we can see in this cross-section, and looking at the image on the right, we can see that the femoral vein highlighted in green is most medial followed by the femoral artery and then the femoral nerve.
Alright, so let's talk a little bit about some nervous structures. And the first nervous structure that we're going to be looking at in this cross-section at the level of the quadratus femoris is the femoral nerve. So, I'd like you to take a look at the atlas illustration to the right and here we can see that the femoral nerve travels into the thigh lateral to the blood vessels. And taking this bit of information, we've highlighted the femoral nerve in the cross-section to the left where it could be clearly seen as being lateral to the femoral vein and the femoral artery. And we can see the femoral nerve being highlighted in green in the cross-section, and as we mentioned before, it will be lateral to the blood vessels in this area.
And, last but not least, we have the sciatic nerve. So, the root of this nerve originate from the lower lumbar and upper sacral regions of the spinal cord and travel downward beneath the gluteus maximus to supply the posterior compartment of the thigh as well as the leg. And we can see the sciatic nerve highlighted in green in both of these images just here. Now, if we take a closer look at the image on the left, the sciatic nerve is sandwiched between the quadratus femoris and the gluteus maximus.
Okay, thanks for sticking with me throughout this tutorial. I know that it's very close to the end, and we're going to recap very quickly going through each of these structures and highlighting what we've talked about today.
So, first, let's recap. We looked at the bony structures starting with the femur and then we moved on to the ischium and the pubic symphysis. From there, we reviewed the other musculature that we see at this level which included the quadratus femoris muscle and then the gluteus maximus muscle followed by the gluteus medius muscle. We saw the iliotibial tract and the tensor fascia latae muscle that attaches to the iliotibial tract.
Then we began to move around to the anterior part of this cross-section and we saw two of the four quadriceps muscles – the rectus femoris muscle and the vastus lateralis muscle. Sitting as the most anterior muscle in the thigh, we have the long S-shaped sartorius muscle and right posterior to the sartorius, we have the iliopsoas muscle. And then moving medially, we run into the pectineus muscle and what appears to be joining the left and right pectineus muscles, we can see the thin pyramidalis muscle just here. Lastly, we found the puborectalis muscle slinging around the rectum.
Moving posterior to the pyramidalis and the pectineus muscles, we found the obturator externus here, and its counterpart, the obturator internus. And after covering all the muscles in this cross-section, we looked at several other anatomical structures at this level. Moving anterior to posterior in the midline, we can see the prostate, the urethra, and the rectum.
To finish off this tutorial, we found the associated blood vessels and nerves in this cross-section. Within the region of the femoral vessels, we can see most medially the femoral vein then the femoral artery, and then we also took a look at the deep femoral artery in this location followed by the femoral nerve as the most lateral structures. And to finish off, we saw the large sciatic nerve sandwiched between the gluteus maximus and the quadratus femoris.
So, that wraps up our tutorial on the cross-section at the quadratus femoris level. Happy studying and thanks for joining me!