0:00

The third basic type of tear is very different.

0:04

And these are the tricky ones. These are the radial tears.

0:07

They also begin typically at or near the tip

0:11

or apex of the meniscus, but they are not circumferential.

0:16

All right? They extend from the central portion

0:20

to the periphery,

0:21

and as they do, they violate the longitudinal

0:24

circumferential collagen bundles.

0:27

So here's what they look like in my

0:29

three dimensional diagram.

0:30

This is what it looks like.

0:32

Uh, this of course, some of you know,

0:34

is the bow tie more about that in a moment.

0:36

But you can see the radial tear, which is extended

0:40

very sharply,

0:42

and you can see how sharp is the abnormality extending

0:45

out to the periphery.

0:46

And the more sagittal images that show it, the longer

0:50

that radial tear.

0:52

Okay? So you can appreciate.

0:54

Now, what do these collagen bundles do?

0:57

They tie together the anterior posterior

1:00

portions of the meniscus.

1:01

So you can imagine with a long radial tear, with violation

1:06

of a lot of those longitudinal circumferential

1:10

collagen bundles, you may get a, a gap at the site

1:15

of the radial tear.

1:17

Here's what it looks like.

1:19

I'm putting in this tear in yellow.

1:21

It's like the radial tie fibers here.

1:24

You can see violation

1:25

of those longitudinal circumferential fibers.

1:29

So it's not surprising. You will see images like this.

1:33

And I can remember very clearly the first time I saw

1:36

something like this, it was in a patient with a tear

1:39

of the anterior cruciate ligament.

1:41

And I spent approximately 20 minutes of my life trying

1:46

to find the missing piece of the meniscus.

1:49

It's not missing, right?

1:51

What you're seeing is a meniscal gap at the site

1:55

of a large radial tear.

1:57

So that's what occurs over a period of time, you will end up

2:01

with a meniscal gap.

2:02

It's like opening a book. All right? Be aware of that.

2:06

Don't waste your time as I did. And the bow tie.

2:11

So normally, particularly as we look in the sagittal images,

2:15

you will see separation

2:16

of the anter posterior horns in a very nice clean fashion.

2:21

And when you deal with radial tears, even small ones,

2:25

these will separate and often have sharp margins,

2:28

not pointed as you can see in the image at the top right.

2:33

Now, let's go ahead and image that one.

2:35

I'm imaging this one right along the axis

2:40

of the radial pair.

2:41

So what do I see? I see nothing.

2:44

This is an absent or empty meniscus.

2:46

It's an old image, but I like it.

2:48

Here's the anterior horn of the medial meniscus,

2:51

and that is fluid where the posterior horn should be.

2:55

So I've imaged this right along the gap associated

2:59

with a large radial tear.

3:02

Large single or multiple radial pairs are frequent in

3:06

discoid lateral meniscus.

3:07

This is a beautiful example of one broad, large radial tear.

3:12

I'll show you later some that are multiple radial pairs

3:15

with discoid meniscus.

3:18

A displaced radial tear is called a parrot beak tear

3:22

resembling the curvature of a parrot beak.

3:24

So let's draw one on this meniscus.

3:27

'cause this is important. This is critical. Let's image it.

3:30

We're gonna image it. Here's my first image. What do I see?

3:35

I see a vertical line, fairly straight, top

3:38

to bottom in the inner margin of the meniscus

3:42

or longitudinal vertical tears we see in the outer half.

3:46

So I'm a little bit suspicious

3:47

that's not a longitudinal vertical tear.

3:50

Let's image it again. We image it again in this particular

3:53

type of tear, that cleft

3:57

is marching in this case toward the tip of the meniscus.

4:00

This is known as the marching cleft sign.

4:04

So the general rule is vertical lines in the inner aspect,

4:08

and I'll say the inner half of the meniscus usually

4:12

indicate radial tears

4:14

or parrot B tears, displaced radial tears.

4:17

Here's a drawing of this particular tear.

4:20

I'm imaging it in the sagittal plane, A, B, and C.

4:25

And here is a broad marching cleft marching from the inner

4:28

margin out toward the periphery.

4:31

Alright? Be aware

4:33

that these radial pairs can look longitudinal vertical,

4:37

but they're in the inner half of the meniscus.

4:41

Now, this also is a critical side.

4:45

Typically when dealing with sagittal images

4:48

and the medial aspect of the knee

4:51

will image the posterior cruciate ligament.

4:54

Here in the next medial image, you should see a lot

4:58

of the posterior horn of the medial meniscus.

5:01

And in the second medial image away from the PCL,

5:06

the entire posterior horn

5:08

of the medial meniscus should be seen.

5:12

So let's look at this case here.

5:15

It's an old case, but you can see here's the PCL,

5:19

there's nothing there.

5:20

Here's my next image.

5:22

And that does not look like a normal meniscus.

5:25

That is abnormal.

5:27

So this is a problem involving the inner aspect

5:31

of the posterior horn, of the medial meniscus.

5:34

And it's obvious when you go to the coronal plane

5:38

that you can see, in fact, rather than the normal situation

5:42

where the posterior horn dives down

5:44

as the posterior root ligament, we can see

5:47

that there is a tear, perhaps a radial tear

5:50

with a meniscal gap.

5:52

That reminds me of a funny story that I remember that we've

5:56

Trained a lot of terrific, uh, bone radiologists at UCSD,

6:01

and they've gone out in the communities

6:03

and they do a lot of mr.

6:05

And a number of years ago, uh, one

6:07

of my ex fellows called me

6:09

and said, you know, I really appreciate your training.

6:12

They always start with that.

6:13

They, I really appreciate your training.

6:15

We're really successful here.

6:16

We're doing a lot of knee, uh, mr uh, examinations,

6:21

and I'm curious that if you had to shorten it

6:24

to one sequence, what sequence would you use?

6:29

And I said, well, I I don't wanna really shorten it

6:31

to one sequence, but if I had to choose,

6:34

it would be the coronal fluid sensitive,

6:36

often fat suppressed image.

6:38

'cause on such an image as shown here,

6:41

you can see menisci bone, uh, bruises, uh, fractures.

6:46

You can see some of the ligaments.

6:48

So I said, well, that would be my favorite, uh, image.

6:50

And he said, well, wait, you don't understand.

6:52

I'm really, really busy.

6:55

And if I wanna, in fact, shorten it to one image

7:00

I have, that's why I said I, I can't recommend that.

7:02

But if I had to shortened the MR examination of the knee

7:07

to one image, it would be a coronal image, fat,

7:12

fluid, sensitive through the posterior aspect

7:16

of the meniscus, particularly the medial meniscus.

7:19

And in fact, I'll go further.

7:21

This is the most important single one half image

7:25

of a knee MR examination.

7:27

All right, that you're seeing that over here.

7:30

That is critical. 'cause a lot happens here.

7:35

Radial tears, root ligament problems.

7:37

So you always wanna study.

7:39

Take an extra few seconds to look at this particular area.

7:43

Posterior horn of the medial meniscus.