The Pelvic Girdle - Video Tutorials & Practice Problems
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1
concept
Pelvic Girdle
Video duration:
8m
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Video transcript
We've previously said that the girdles are how the appendicular skeleton connects to the axial skeleton. Well, now we're going to talk about the pelvic girdle, and the pelvic girdle is how your legs connect to the core of your body. The pelvic girdle is just made of 2 bones, 2 bones only, the right and the left coxal bones. Now, those coxal bones, though, are also part of what we call the pelvis, and the pelvis is gonna be the coxal bones plus the sacrum. And when you think of the pelvis, that's that entire ring of bone that sort of surrounds your pelvic cavity. And you can also think of it as how the weight of your body that's carried by the vertebral column carried by your spine gets transferred into your hips and then down into your legs. Alright. But now we're just focusing on the coxal bone because that makes up the pelvic girdle, and so the coxal bone is also gonna be called the ossococci. Oss cocci, that's the Latin term for it. You should be familiar with that. You can probably use them interchangeably on a test. They're both technically correct. Now the os coxae or the coxal bone, that's actually gonna be formed by 3 fused bones. So even though the coxal bone is just one bone, we're gonna go into some detail about the 3 bones that fuse to make it up. Before we do that, let's look at our image. We have the full pelvis here shown with the sacrum there and bone color in the back with the color coded coxal bones on either side. We're color coding the different bones that met that fuse to make up that bigger coxal bone. We also, on the right here, have a side view of that coxal bone, again, color coded. So the first bone that makes up the coxal bone is going to be the ilium. The ilium is gonna be this superior kind of flattish region, and we can see that in purple here labeled a in this drawing. I also have a coxal bone here, a right coxal bone, and you can see that this upper part is sort of this kinda flattish plate. Now the bone itself isn't flat. A lot of times it looks kinda flat in, drawings. You have sort of this flattish plate on the top, but then there's a real sort of twist in the bone to get to the two bones on the bottom, which we'll talk about in a second. But this flat part on the top, that's the ilium. And the thing that you'll notice about it is it has this big sort of round crest on it that you can see here. We've labeled it a in these two pictures here, that round crest. That round crest is the iliac crest. And if you put your hands on your hips, you feel your hip bones right there, you're touching your iliac crest. You can feel that it comes to the front of your body and sort of wraps around into your back, and it's this big attachment point for muscles. Now one way I remember the ilium is it that bone on the top. Well, when I say iliac, it kind of sounds like I like, and I could say to someone, Hey, I like your iliac crests. And if I said that, I'd be saying, hey, you have nice hips. Now please don't actually say that to someone. That would be weird and creepy, but it helps me remember it. Alright. So as we move down, we're gonna talk about the ischium. The ischium is gonna be the lower posterior region, the region in the back. Alright. These are the bones you sit on. Sometimes people call them your sit bones. On a column, just your butt bones here. Right? If you got a bony butt, these are the bones we're talking about. Alright. So you can feel those bones in the back. And the way I remember the ischium, well, this is gonna be kinda round because, well, your rear end is round. And so the roundish ischium is in your rear, and we can see that here in pink. That's gonna be the ischium, and here on the side, you can see how it's nice and round. We can look at the, bone here. This is that roundish ischium in the back. It's nice and rough, if you feel the real bone because it has all these muscle attachments there. Alright. So the roundish ischium is in the back, and then you'll probably notice that there's this hole in the coxal bone. That hole, we're just gonna say here, is called the obturator foramen. And it's just, formed. It's just a hole between the ischium in the back and the pubis in the front. It doesn't have a lot of function. There are some nerves and blood vessels that pass through it, but beyond that, it's just the hole that's pretty noticeable when you look at the coxal bone. Alright. So now we're gonna move over and look at the pubis, also just called the pubic bone sometimes. And well, if the ischium is the posterior region, well, then the pubis is going to be the lower anterior region. It's the part of the coxal bone that is in the, front. Alright. So the front, you can feel this as well. It's the bone right in front, the pubic bone that's sort of just sort of just above the region of the genitals, and it comes together. The 2 coxal bones come together and meet at the pubis synthesis. Right? That pubic symphysis is where these 2 come together, and there's gonna be a cartilage that forms a joint right there. So that pubic symphysis, you can see here, is c. And we're just gonna write here that that is going to be the joint between the right and the left pubis. Alright. The way I remember the pubis or the pubic bone, well, I say that pubis is pointy. So the ischium, I have that roundish ischium and the pointy pubic bone. So that's gonna be the pubic bone. That's how I keep those 2 separate in my head. Alright. The last thing that you're probably really gonna notice about this coxal bone is this round socket right here, and we have this round socket here, circled in d. That socket is the acetabulum, and we're gonna say here that is the hip. The hip socket. And the hip socket is actually formed by all three bones. So when you look over here, we see that the dividing line between where these bones came together is sort of in the middle of that acetabulum. Now, this is where the femur comes in and joins, so you have that big round hit on the femur and it fits in there really nicely. Now the way I remember and I orient the bones here is that I say, well, the if the pubis is pointy, that's facing toward the front. Well, for the femur to come in here, that has to be facing out to the side. So if I'm holding this bone, I put the hips on the top, the pointy pubis in the front, and the socket, the acetabulum out to the side, well, this then would fit on the right side of my body, so this must be the right coxal bone. Alright. So I'm gonna say here with the pubis pointy front, the acetabulum is to the side. Alright. The last thing just about these joints, if you remember when we talked about the pectoral girdle, we said how mobile that shoulder joint was because you're able to not just move the bone around in there a lot, but you can also move the girdle. Well, now you'll notice that acetabulum is really deep. So that just on its own limits a little bit how much this femur can move in it, but also the other joints here. Well, I can take the sacrum and I can line it up. Now this joint that you make there, that's technically a movable joint, but it doesn't move much. It's a really firm joint, because the purpose here is to be transferring weight that's carried by the sacrum down the spinal column and into those hips. Now, likewise, at the, pubic symphysis in the front, well, that's a cartilaginous joint, so there's a little bit of flex there, but not much. Now during pregnancy, some hormones will loosen that up a little bit. It'll actually get a little bit wider and give it a little bit more flex, but still not much. So compared to the pectoral girdle, this pelvic girdle has very little movement in it. Alright. We're gonna be talking about this a little bit more going forward, especially we're gonna look at some differences that are regular between male and female pelvises, and I'll see you there.
2
example
The Pelvic Girdle Example 1
Video duration:
3m
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Video transcript
Our example says on the image below, label the 3 smaller bones that make up the coxswain and identify whether the left or right coxal bone is shown. Alright. And we have a picture of a bone here, a real bone, and we're clearly looking at the side view of a coxal bone. So the first thing that I'm going to do to label the bones is I'm going to draw the dividing line of where those bones meet. So do you remember where that dividing line goes? Well, when I draw it in, I'm gonna draw it in and remember it meets in the acetabulum here. And so this is roughly where this dividing line is gonna be, dividing that bone on the top and then dividing the 2 bottom the bones on the bottom, we're just gonna sort of draw roughly straight down from there. Then we have this obturator foramen, this hole in the bone, but this dividing line is gonna cross over and it's gonna divide it down there as well. Alright. So now we have our 1, 2, 3 bones. Let's try and name them. Alright. So what's this one on the top? This is that sort of larger kind of plate like bone. Remember? Well, when I look at it, I had that kind of creepy memory tool where I said, I like your iliac crest because this is that big iliac crest there. And iliac crest, that's your hips. And so the iliac, that refers to the ilium is the bone. Alright. So that big plate like bone on the top, the ilium. Next, I'm gonna look down and well, do you remember what this bone down here would be? Well, as I look at that, I see how round that is, and I well, I know that my rear end is round, like that bone, and I had that memory tool where I said, well, the roundish ischium makes up my rear end. So the roundish ischium. Ischium is the bone. And then finally, I'm gonna look at this bone here. Do you remember what bone is left? What are we gonna name that? Well, this is pointy. I see that sort of point on the bone there, and I said that the pubis is pointy. Alright. So that's gonna be the pubis there. Now we have to determine, is this the right or the left? Well, as I do that, I can see here that I'm looking at the acetabulum. So that means that the hip, the femur, is going to fit into the hip socket there. So this has to sort of be on the outside of the body. And then I said, well, also, the pubis is pointy and it's pointing to the front. So I always try to imagine how are these bones gonna fit in my body, and if I think about this, the pubis is in the front and then the femur has to fit into this acetabulum. Well, if I were to line that up on my body, the way that would work is if it were on the left. All right. So this is a left coxal bone that we're looking at here with the ilium, the ischium, and the putis. Alright. Like always, more problems to follow. Give them a try.
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Problem
Problem
On which bone is the acetabulum found?
A
Ilium.
B
Ischium.
C
Pubis.
D
A-C are all correct.
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Problem
Problem
When comparing the pelvic and pectoral girdles, which statement is incorrect?
A
The articulation between the pectoral girdle and the axial skeleton is smaller than the articulation between the pelvic girdle and the axial skeleton.
B
The socket of the hip joint is much deeper than the socket of the shoulder joint.
C
There are more individual bones in the pectoral girdle than the pelvic girdle.
D
The pelvic girdle allows for a greater range of motion than the pectoral girdle.
5
concept
Differences Between the Male and Female Pelvis
Video duration:
3m
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Video transcript
When learning about the pelvis and the pelvic girdle, you are very likely to see questions about differences between the male and female pelvis, so we're gonna go over that now. Now this all comes down to the fact that the shape of the pelvis tends to differ between males and females. Now with all things in anatomy, there's variation around this, but an experienced anatomist can identify the sex of a skeleton correctly about 97% of the time just by looking at the pelvis. There's no other bones that show that regular sex difference. So how do they do it? Well, first off, you can look at the general appearance. In males, this pelvis is a little bit taller, and it tends to be more narrow when you're looking at it in that direction. It's so it's we're going to say that it's narrow, and the bones are also just kind of heavier. So I'm going to say the bones are narrow and heavy, and by that, we just mean they're thicker. Now in comparison, we look at the female pelvis. You can see it's kind of shorter and wider over here, and so I'm gonna write here wider. And also, well, if the male pelvis is heavier, the female pelvis is a little lighter. The bones are just a little bit thinner. Next, we can look at the angle of the pubic arch, and the pubic arch is right here where the coxal bones come up and meet at the pubic symphysis. And you can see that this angle is different between males and females. In males, this angle tends to be a little bit sharper, or we'll say a little bit more acute. And in females, we can see that this angle is going to be wider, or at least it tends to be wider or more twos. We can also look at the shape of the pelvic inlet, and the pelvic inlet well, it's a little bit best seen from a top down view, a purely top down view. But it's if you draw a circle sort of around where the pubic symphysis is, it's sort of that narrowest part of the pelvis where it makes a ring. In males, what we actually say it doesn't make a ring, it's a little bit more heart shaped. I'm just gonna write a heart there, more heart shaped, and just kind of closer together. It's sort of a little bit pointier in the front and narrower. Where in females, when you look at that shape, it's just much more rounder, and we're gonna say more of an oval shape. Now what gives it that heart shape is that in males, the sacrum sort of curves under the sacrum and the coccyx, sort of curve underneath the pelvis a little bit more. And in females, that sacrum and that coccyx sort of point a little bit more downward. They don't curve under the pelvis nearly as much, giving it that more round appearance. Now these differences, it's largely believed, are due because the female pelvis is adapted for birthing. During pregnancy, a big bony structure known as a fetus or a baby is developed right here. And then during birthing, it has to pass through this pelvis, and that bony structure is going to pass through the pelvis much easier if it's a rounder, wider pelvis rather than a narrower pelvis. Okay. We're going to practice looking at these differences more in the example to follow, so give it a try.
6
example
The Pelvic Girdle Example 2
Video duration:
3m
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Video transcript
Our example says that below, 4 pelvises are shown. 2 are shown from the front and 2 are shown from above. In each view, 1 pelvis is from a female and one is from a male. We need to identify which pelvises we believe to be male and which we believe to be female. Then we need to indicate at least one anatomical feature that allowed us to differentiate the 2 by marking it on the picture. Alright. So we have 2 images here. The image on the left clearly shows 2 pelvises as we're looking down on them, and the image on the right, we have 2 pelvises from a front view or an anterior view. So let's start on these 2 on the left. Which one do you think is more likely a male pelvis, and which one do you think is more likely a female pelvis? Well, when I look at it, the thing I queue in on is this shape here. As I look down through the pelvis, I'm gonna circle this, and that's the shape of the pelvic inlet, that ring around the pelvis there. And this one on the left, it looks kinda round and and kinda wide, especially when I compare it to this pelvis on the right. This pelvis on the right has that sacrum sort of coming underneath. As I draw that shape, it comes out much more kinda heart shaped there. Right? That heart shaped pelvic inlet, that's more likely to be part of a male pelvis, and that bigger, rounder, more oval shaped pelvic inlet is more likely to be part of a female pelvic inlet. So what's the anatomical feature we use to identify that? We use the pelvic inlet. Alright. Let's look at these 2 on the right. Take a look. Which one do you think is more likely male? Which one is more likely female? Well, when I take a look, what I notice is that this pelvis on the left, it's pretty tall, and it's also relatively narrow, at least for how tall it is. Well, this one on the right, that's pretty short, and it's very wide, again, at least for how short it is. And I remember that a tall, narrow pelvis is more likely to be a male pelvis, and a shorter, wider pelvis is more likely to be a female pelvis. But the thing that really cues me in here is something else. And that's when I look at this, I look at this angle right here. That's the angle of the pubic arch. And do you see on that pelvis? It's a real sharp angle. It's an acute angle. Where on this pelvis, it's very wide, or rather, it's an obtuse angle. Alright. That sharper angle is more likely to be part of a male pelvis, where the wider or obtuse angle is more likely to be part of a female pelvis. And the anatomical structure that I use to identify that is the shape or the rather the angle of the pubic arch. Alright. With that, we've answered the question. More problems to follow. Give them a try.
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Problem
Problem
How does the angle of the pelvic arches differ in male and female pelvises?
A
The angle of the male pelvic arch tends to be more acute than the female pelvic arch.
B
A female's pelvic arch tends to be rounder to accommodate the head of the baby.
C
The female pelvic arch tends to be more heart shaped than the male pelvic arch.
D
The pelvic arch is not a reliable indicator of sex.
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