0:01

In the last vignette, we looked

0:02

at a lateral discoid meniscus.

0:05

By the way, a vast, vast, vast majority

0:09

of meniscal abnormalities, like

0:12

the discoid meniscal abnormality,

0:13

happen on the lateral side.

0:15

In fact, if you see a lateral, or if you see a

0:17

discoid meniscus on the medial side, question

0:20

yourself if it's actually a discoid meniscus.

0:22

It can happen.

0:23

I've seen a few cases.

0:24

But the vast majority

0:26

happen on the lateral side.

0:27

That's just a little caveat for you guys.

0:29

So here's another case of a discoid meniscus.

0:32

With a slight variation, and

0:33

let me talk to you about that.

0:35

Here is a sagittal T1.

0:36

Already we can tell that there's something

0:38

wrong with this lateral meniscus.

0:41

It's very, very thick.

0:42

It has abnormal globular signal, but it

0:45

doesn't reach the articular surface, so I

0:47

don't think it's actually torn within the body.

0:50

And it's sort of bunched up over here,

0:52

and there's a big gap between the

0:55

capsule, posteriorly, and, uh, posterior.

0:59

very posterior margin of your lateral meniscus.

1:02

So what's going on?

1:03

So I can already tell you that there's been

1:05

an injury or there's been separation of

1:08

your meniscal capsule ligament posteriorly.

1:11

And this is called the Risberg

1:14

variant of discoid meniscus.

1:17

To get a better idea of its anatomy and what

1:20

it looks like on the axial plane, we revert

1:24

back to our thin slices, which in my case are

1:27

these DES sequences that show this

1:30

fluid gap, and let's reconstruct this image

1:34

through the meniscus and see what it looks like.

1:37

I'm going to go back to one-on-one,

1:38

bring down my sagittal DES,

1:44

triangle, reconstruct, and here we go.

1:48

I'm going to zoom in just so you guys can

1:50

appreciate the abnormality a little better.

1:53

So again, what I'm looking at is,

1:56

let's find lateral and medial.

1:57

It's very easy to do.

1:59

We know the lateral side is here, because

2:01

here's the fibula, and here's our abnormal

2:03

meniscus, which is right over here.

2:05

Let's orient our plane, so it

2:07

goes right through that area.

2:09

Let's raise it up,

2:13

so we know we're right through that plane,

2:17

and here, we're actually

2:20

right through that plane.

2:21

So let's go and zoom back out a

2:23

little bit on this, and then turn it.

2:29

So where is the meniscus, right?

2:30

So it has to be over here.

2:32

Here's the meniscus.

2:33

And why does that meniscus look so funky?

2:36

So let me first show you

2:38

where I think the meniscus is.

2:41

This is the root, the

2:43

anterior root of the meniscus.

2:45

This is part of the anterior horn.

2:48

It takes a funny turn over

2:49

here because it's bunched up.

2:51

It's bunched up.

2:51

This part of the meniscus has been

2:53

shifted anteriorly because there's no

2:55

attachment here to the posterior capsule.

2:58

All this fluid is this fluid gap

3:01

that we're seeing back here, okay?

3:04

That's the fluid gap we're

3:05

seeing right over here.

3:07

So let me, if I can, zoom this up

3:10

a little more and actually draw

3:12

what I think the meniscus is doing.

3:15

Here is the outline of what

3:17

I think the meniscus is.

3:19

Okay, that's what the meniscus looks

3:22

like currently because you are missing

3:26

attachment to the posterior capsule.

3:29

This fluid-filled area is the space

3:33

that has been left by this meniscus

3:36

that has been translocated anteriorly.

3:40

What should that meniscus have looked like?

3:44

So it should have looked like if it

3:46

was just a discoid meniscus, it should

3:48

have looked something like this.

3:50

It would still be a discoid meniscus, right?

3:53

But now you've lost the attachments.

3:55

That's why this portion of your discoid

3:59

meniscus has translocated to this position.

4:05

So this is called a Risberg variant.

4:08

And this is more problematic because every

4:10

time the patient flexes or extends his

4:13

knee, the discoid, this bunched-up part

4:17

of the meniscus keeps moving back and

4:19

forth, back and forth, back and forth.

4:21

So that can cause problems of locking.