0:00

Okay, here are three sagittal

0:01

gradient echo sequences.

0:04

On the left, we have a 20-day-old.

0:06

In the middle, we have an eight-month-old.

0:08

And on the right, we have a 14-year-old.

0:10

So this, I think, best illustrates how an

0:14

infant really isn't a small child, and a

0:17

small child really isn't an adolescent.

0:20

Look at the difference in the

0:22

cartilage in these three patients.

0:25

Here, there is a very large cartilage.

0:29

heterogeneous gray appearance

0:31

of the epiphyseal cartilage.

0:34

The amount of epiphyseal cartilage,

0:37

zonoprovisional calcification, and the

0:40

metaphysis right here, the spongiosa, is a

0:43

lot wider, a lot bigger, a lot more involved.

0:46

Look at the degree of darkness, if

0:50

you will, of your medullary cavity.

0:52

You notice that it's not as dark; that

0:53

means that it's not as well trabeculated.

0:55

You still have a lot of hematopoietic marrow

0:58

that's contributing to the signal here.

1:00

Uh, contrast that to a slightly

1:02

older child, eight months old.

1:05

Look how much more differentiated

1:07

some of these structures are.

1:08

You can get a nice clear view

1:10

of the content of the epiphysis.

1:12

You can see the articular cartilage is

1:14

very well defined here, nice and bright.

1:16

You can see the physis; the trilaminar

1:18

appearance is getting to be what we

1:20

looked like, what we described previously.

1:22

You can see again.

1:23

This is the hypertrophic zone of cartilage.

1:26

This is the zone of provisional

1:28

calcification; that's dark.

1:29

And immediately above that is the spongiosa

1:32

of the metaphysis, very clearly seen.

1:35

And the distance between these three structures

1:37

is a lot smaller than the distance over

1:39

here, meaning that this has less growth

1:42

potential now, really, than this does.

1:44

Okay?

1:45

Now, finally, let's look at somebody who is

1:48

approaching adulthood, but not quite there yet.

1:50

We know they're not quite there yet

1:52

because the physis is still open.

1:54

Whereas this person, an adult, the

1:56

physis would be completely closed.

1:58

Uh, we can't appreciate the tri-

1:59

laminar appearance very well anymore.

2:01

Maybe a hint of it over here.

2:03

Here's the dark area.

2:04

Here's a little bit of brightness.

2:05

And so this brightness really is

2:07

just still the hypertrophic cartilage

2:10

cells that we're looking at, right?

2:12

But look how much more of it is still open.

2:14

has been ossified.

2:16

And this, the majority of what's left over

2:19

on the periphery, is articular cartilage.

2:21

And look how the articular cartilage

2:23

isn't quite as bright as the articular

2:25

cartilage in the younger person over here.

2:29

Also, look at now the physis or the area

2:34

where metaphysis transitions to epiphysis.

2:36

Every so often as you go through there, there

2:38

are areas where there's a little bridge.

2:41

Right?

2:42

So what's happening is this physis is

2:44

about to close, and that's what happens.

2:46

It doesn't close all of a sudden;

2:47

you know, one day it's bright,

2:48

and the next day it's all black.

2:50

What happens is little areas like this,

2:52

little tongues of tissue, if you will, come

2:54

together and bone forms at that location.

2:58

And eventually, when this is

3:00

completely dark, that means the

3:01

physis has completely scarred down.

3:04

Uh, so we call it a scar.

3:05

It's not really a scar.

3:06

It's scarred down.

3:07

Uh, and you no longer can differentiate

3:09

metaphyseal bone from epiphyseal bone,

3:11

and you've got complete maturation.

3:13

But it's a process.

3:15

It goes from here, to here, to here.

3:17

One other thing I want you to notice on

3:19

this sort of adult pattern is, in the

3:21

articular cartilage, in the weight-bearing

3:23

surfaces, there's a little bit of darkness

3:25

in the articular cartilage that you

3:27

really can't appreciate in any of these.

3:29

And I wonder if you can guess why that is.

3:32

Well, what's happening with the adolescent?

3:34

They're running, they're jumping,

3:35

they're having activities.

3:36

So some of the fluid in the weight-

3:38

bearing surfaces is getting taken away.

3:42

So there's some degree of

3:43

desiccation, if you will, that's happening.

3:45

And because of that, you do

3:46

get some areas of darkness.

3:48

So it's important not to see

3:49

that and call it pathology.

3:51

It's important not to call

3:52

that area of darkness

3:53

cartilage damage.

3:54

That is just simple, normal

3:57

wear and tear that happens.

3:58

Often it's located at the

3:59

weight-bearing surfaces.

4:01

So you can see, again, you can see also

4:03

here in the proximal tibia, here, and here.

4:06

So this is a really good example, I think,

4:08

of the progression of how the secondary

4:11

ossification center in the epiphysis expands,

4:14

the marrow gets filled with trabecular

4:17

bone, and you have increased susceptibility

4:19

and eventual closure of the physis.

4:23

And you no longer have growth

4:26

and maturation has been achieved.