0:00

<v ->Articular cartilage is extremely well hydrated.

0:05

It possesses a great deal of water, right?

0:09

And because of that,

0:11

its characteristics are very, very important.

0:14

I mean, look at this table,

0:16

this small table at the bottom here

0:18

indicates that if we look at a wet weight

0:22

of articulate cartilage, 65 to 80% of it relates to water.

0:29

So we're talking about extreme hydration of this tissue.

0:34

Now there are some dry components,

0:37

the proteoglycan's the collagen.

0:39

For our discussion today, we will concentrate on collagen,

0:44

and why is that?

0:45

Because you see it's the collagen that transmits the force

0:50

striking the surface of articular cartilage

0:53

through the articulate cartilage

0:56

so that it reaches the subchondral bone.

0:59

So you have to know something about the collagen

1:03

within the articular cartilage.

1:05

So let's use some simple diagrams and drawings that I made,

1:10

a histology on the left

1:12

to show you the general composition of articular cartilage.

1:17

If we look at it histologically, we see a variety of cells

1:22

often arranged in rows of different shape, all right,

1:25

extending down deeper and deeper.

1:28

That's the noncalcified articular cartilage,

1:35

articular cartilage.

1:36

We reach the area of my red rectangle

1:40

which is the tidemark.

1:42

It is a histologic landmark shown here

1:46

and it separates the noncalcified cartilage

1:50

from a layer of calcified cartilage below it.

1:54

As we're gonna learn later on,

1:56

shear forces are particularly detrimental to the tidemark.

2:02

So that's gonna become imp to us a little bit later on.

2:06

Beneath the calcified cartilage,

2:08

a thin layer of compact bone is shown here and beneath that,

2:14

we can see the subchondral bone.

2:17

And by the way, the marrow chambers

2:19

that we've already are talking about.

2:22

Now we add the collagen.

2:25

So let's look at the architecture of this collagen.

2:29

At the surface of the articular cartilage,

2:32

we deal with parallel layers of collagen fibers

2:37

with a classy name known as the lamina splendens, right?

2:43

This leads to a lot of the very unique characteristics

2:47

of articular cartilage.

2:49

Below that area, we have these arcades of collagen

2:54

extending from the superficial to the deep portion

2:59

through the tidemark and into the calcified cartilage

3:03

and compact bones.

3:05

These arcades were described by Beninghoff

3:09

and every single orthopedic surgeon knows what the arcades

3:13

of Beninghoff are.

3:15

So you can see that if a force were applied up here,

3:19

that these arcades would allow transmission of that force

3:23

deep down into articular cartilage, okay?

3:29

Now let's look at this in a little more detail.

3:33

I want you to look at that layer of compact bone,

3:37

compact dense bone.

3:40

In the human body, there are two forms of compact bone,

3:44

not one, two.

3:46

The first of these we call cortex.

3:50

Cortex is compact bone formed by the periosteal membrane

3:56

through intramembranous bone formation.

4:00

So when you look at the surface of any bone here,

4:03

the radius, that is cortical bone,

4:06

but there's a second type of compact bone that is different.

4:11

And the term is not cortex,

4:14

this is called a subchondral bone plate

4:17

because you see this compact bone formed by cartilage

4:23

through endochondral bone formation, not intramembranous.

4:28

So when you look at a radiograph,

4:30

you look at a CT and you see a white line

4:35

or curve a linear line at the end of a bone,

4:38

don't call it cortex, it is is a subchondral bone plate.

4:43

It is not cortical bone.

4:47

If we go to electron and microscopy,

4:49

we can see that collagen that we've already drawn

4:53

for you in this, over here,

4:56

here is the lamina splendens,

4:59

layers of collagen at the very surface.

5:03

We then move on to the blue area,

5:05

the blue area, or the curving collagen fibers

5:09

just beneath the lamina splendens.

5:12

And then as we go deeper down here in the yellow arrows,

5:17

we're looking at the lower portion of arcades

5:20

that become almost parallel in their architecture

5:26

and in their direction.

5:28

So this is the collagen framework of articular cartilage.