Interactive Transcript
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Okay, let us take a look crudely
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with a cartoon diagram of what the hyaline cartilage at birth looks like
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and then we'll talk about some of the development.
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We have a nice blank screen here.
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I'm going to use a blue color just so you have an idea of what cartilage is.
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And typically, I think of cartilages as being blue.
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Let's just draw a nice big area here.
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So think of this as the end of the long bone.
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This is the epiphysis.
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The metaphysis would be somewhere over here
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and the diaphysis would be somewhere down here.
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So right now we're concentrating on this part, which is the epiphysis.
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I'm going to just call it EPI. Okay?
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So when you're first born,
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it's basically just a bunch of cells, bunch of cartilage cells.
0:49
They're very tightly packed.
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And there are actually three components to this epiphysis.
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There's what's called the articular
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cartilage, which is at the surface. We're going to call that A for articular.
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There is the majority, which is going to be
1:05
sort of in the center here, and that's called the epiphyseal cartilage.
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The whole thing is the epiphysis and the majority is called epiphyseal cartilage.
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And there's an area close to here,
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the metaphysis, that's going to be the physeal cartilage.
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And there's different composition of each section.
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And actually, it depends on what the chemical and cellular
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composition is to call this the articular, epiphyseal and physeal cartilage.
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Let's talk now a little bit about the articular cartilage.
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The articular cartilage, as I said, is the outermost layer of the epiphysis.
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It contains three major things.
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One, it's called aggrecan,
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that's not very important.
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Two, it has type 2 collagen.
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And three, the most important thing, is it has a lot, a lot, a lot of water.
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It's about 70% water by volume.
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That's why on T2-weighted images and STIR images, the articular cartilage
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looks very, very bright because of all the water that's unbound.
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Okay? So, major thing to realize is it has a lot of H2O in the articular cartilage.
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The articular cartilage also has several zones from the outside to the inside.
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We're not going to worry so much about that.
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The really important thing is the very
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inner zone, which is calcified, and that often looks a little dark in MRI.
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And I'll show you that as we go through these images.
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The second thing I want to concentrate
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on is the epiphyseal cartilage, which is this big area over here.
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This is all epiphyseal cartilage.
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In that epiphyseal cartilage, you've got chondrocytes, collagen,
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glycosaminoglycans, and also has lots of water.
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But the water in here, H2O in here,
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are often bound to molecules, very tightly bound to molecules.
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Because the water is tightly bound,
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it's going to have a different signal characteristic
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on MRI. It's often going to look a little darker, actually a lot darker
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on the fluid sensitive sequences such as T2 or STIR.
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Okay?
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And you've got vessels coursing through there that actually we're going to talk
3:14
about how that contributes to
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contribution to forming a bone later on.
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And finally, the physeal cartilage,
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which is this area over here next to the physis.
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It's about 75% volume of cells.
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So you think because there's so many cells there, it's going to be not so much water.
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But the cells here are actually very big
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and the intracellular component has a lot of water.
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So that also an MRI is going to look very, very bright.
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As a review, articular cartilage is going to be
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bright, physeal cartilage is going to be bright,
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and the epiphyseal cartilage, which is the majority here, is going to be very dark.
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