0:00

We have a teenager here with lateral knee

0:03

pain, and one of the most common reasons

0:05

for lateral knee pain is a discoid meniscus.

0:09

There's stuff out there that says, okay,

0:11

you need to count the number of bow ties on

0:13

the lateral view, make sure it's not more

0:15

than four, or look at the measurement of

0:17

the body on the coronal view to make sure

0:19

that it's not bigger than 11 millimeters.

0:22

But sometimes that becomes a little

0:23

problematic in the pediatric population,

0:25

because one, it may be a small knee, and

0:28

the 11 millimeter rule may not apply.

0:31

Oftentimes, we're getting slice thicknesses that

0:33

are much smaller than the typical 4 millimeters.

0:37

So counting bow ties and saying a

0:39

cutoff of 4 may not be relevant when

0:41

your slice thicknesses are so thin.

0:43

It may be 6, 7, 8.

0:45

So I don't like to use that rule.

0:46

I like to look at the shape of the meniscus.

0:49

And I want to, when I do that, I get a better

0:51

idea, an overall idea of what's going on.

0:53

I want to see how much

0:54

encroachment there is of that body,

0:57

close to the intercondylar notch,

1:00

and I compare it to the other side.

1:02

That's something I like to think about when

1:04

I look at the shape of the menisci.

1:07

Rule number one, the posterior horn,

1:12

here, should always be at least the same

1:14

size or bigger than the anterior horn.

1:17

So let's go to the other

1:17

side to give you that clue.

1:20

So the posterior horn is at least as

1:22

big or bigger than the anterior horn.

1:25

Okay.

1:27

Rule number two, when we look at the

1:31

meniscus, there should be no

1:35

high signal that extends to an articular

1:37

surface that would indicate a tear.

1:40

And finally, if we have the meniscus and

1:44

we're suspecting some kind of injury,

1:46

there should be at least on one slice some

1:48

attachment of that posterior meniscus to

1:51

the capsule, which is known as the tear.

1:53

Posterior meniscus capsular ligaments,

1:56

or coronary ligaments, depending

1:58

on what literature you use.

2:00

So, as I look at this, on the

2:01

lateral side, I see that, in fact,

2:04

it's a different shape, isn't it?

2:06

It's a more globular shape, it doesn't have

2:09

a clear demarcation, uh, where there's a

2:11

nice triangle posteriorly, uh, and nice

2:14

triangle anteriorly, but there is still

2:17

maintenance of attachments to the capsule.

2:21

So this is a discoid meniscus.

2:23

Now I said, I look at the shape.

2:25

The best way to look at the shape

2:26

is actually on the axial projection.

2:28

If you take a conventional axial projection,

2:31

for example, something like this, fat suppressed

2:33

fluid sensitive sequence, and we get to the

2:35

level of the meniscus, it's hard to see where

2:37

exactly that meniscus is, because the slice

2:40

thicknesses are so big, and the plane at which

2:44

you are imaging the meniscus, if you look at the

2:46

sort of image over here, this reference line.

2:49

It doesn't go through the entire

2:50

meniscus in the plane that you want.

2:52

So because of these limitations, I like to

2:56

reconstruct my own images for the meniscus.

3:01

So for that, I'm going to go to one on one and

3:04

I'm going to bring down my thinnest slices.

3:06

My thinnest slice is going to be

3:07

this one, which is a sagittal desk.

3:09

Okay.

3:10

Now I'm going to take this image and

3:12

reconstruct it such that My axial plane

3:15

goes right through that meniscus, okay?

3:18

For that, I'm going to go on to and hit

3:21

this little triangle on the right, and

3:24

I'm going to say 4 on 1, and that will

3:26

automatically generate these orthogonal images.

3:30

So, it doesn't help to have

3:32

conventional axial and sagittals.

3:34

What I want is an image that I can define

3:37

that goes right through my area of interest.

3:38

So, I'm going to look right over here.

3:40

So, I'm going to orient this

3:42

such that it goes like this.

3:44

And put it right here on that meniscus.

3:48

So on the coronal plane, it's

3:50

going right through the meniscus.

3:51

Now let's go to the sagittal plane.

3:53

On the sagittal plane, it's

3:54

not quite the way I want it.

3:56

I'm going to rotate that just a little bit.

3:58

And now, on both planes, I am going

4:01

right through that meniscus, aren't I?

4:05

So as I scroll back and forth, I'm going

4:06

to zoom in a little bit on this image.

4:08

As I scroll back and forth on here.

4:14

So this actually isn't.

4:16

The C, this one still gives me

4:17

a direct corona, a direct axial.

4:20

What I want is to look at this image.

4:22

This image is a little rotated.

4:23

I'm going to rotate it the way I want it.

4:26

Which is this way.

4:29

And now that's better.

4:30

So, this is the normal side.

4:32

This is the medial side.

4:34

And look at this nice C shape of the meniscus.

4:37

Right?

4:37

Thicker on the posterior aspect.

4:39

Right?

4:39

A little thinner anteriorly.

4:41

You can see the meniscal roots

4:42

very, very well anteriorly.

4:44

Meniscal roots very, very well posteriorly.

4:46

Now let's go to our side that's abnormal.

4:49

And here it is.

4:50

Let's convince you that that is

4:51

in fact what we're looking at.

4:53

Let's go to that side.

4:55

And here's a line right through the meniscus.

4:58

And here's a line right through the meniscus.

5:00

So this indeed is our lateral meniscus.

5:04

Look at the shape of this lateral meniscus.

5:05

I'm going to outline this for you.

5:08

I'm going to zoom it up.

5:11

I'm going to bring it out.

5:12

So here is your meniscus.

5:17

And here are the roots going anteriorly.

5:20

And we can't see the posterior roots very

5:22

well, but this is where it would go through.

5:24

Now look at the shape of that meniscus.

5:26

It's very, very globular.

5:27

That's why we call it a discoid meniscus.

5:30

It should look something like this.

5:35

But this part of it here, persists.

5:39

So what can happen?

5:40

Because it's a, it's an abnormal discoid

5:41

meniscus, you can have, it's more prone to

5:44

being torn, it's more prone to having little

5:47

free fragments come into the intercondylar

5:49

surface over here and cause locking.

5:52

So lots of problems associated with this.