0:00

Moving on to the discoid meniscus.

0:03

Much more commonly seen on the lateral side than

0:06

on the medial side.

0:07

It may be bilateral described particularly in certain Asian

0:12

con, uh, countries in both men

0:14

and women fairly frequent finding.

0:17

There are some criteria

0:18

that have been included in the literature.

0:21

A coronal width greater than 14 millimeters or three

0:25

or more sagittal, five millimeter images

0:29

in which the two portions of the meniscus remain connected.

0:34

These have been described

0:35

or classified by the Watanabe classification into those

0:40

that are complete, those that are incomplete,

0:44

typically those two are stable to probing.

0:46

And then what is called a rice bird type of discoid meniscus

0:51

where there are a few connections

0:53

or stabilizing features of the posterior horn

0:56

of the lateral meniscus may be mis uh, missing ptl,

1:00

meniscal ligaments and root ligaments.

1:03

And therefore there is a hypermobile posterior horn.

1:07

Just to show you some pictures of what these look like

1:11

on your left, an incomplete disco

1:13

and on your right, a complete disco.

1:16

There are several characteristics of the patterns of failure

1:21

that we see in eight discoid meniscus cleavage

1:24

or horizontal tears.

1:26

And I've already mentioned these may not violate

1:29

a meniscal surface, single double

1:32

or even triple radial tears

1:35

as shown in this particular example.

1:39

Central holes that are created between the central

1:42

and peripheral margins of the discoid meniscus

1:46

as shown in this particular example.

1:50

Now, one of the interesting aspects

1:52

of in fact a discoid meniscus is that these may be unstable

1:58

and indeed this may relate to problems

2:01

of the meniscocapsular tissues.

2:04

You may see these related to altered signal intensity,

2:09

and this has been likened to a Roman candle firework, right?

2:14

So this is what it looks like when you're dealing

2:17

with meniscal capsular injury in a person

2:20

who has a discoid lateral meniscus.

2:24

It's not surprising then that you may end up

2:26

with displacement of that discoid meniscus.

2:30

These have been described into the quadrants

2:34

to which the meniscus is displaced.

2:36

Most common, uh, pattern

2:38

that we would see is a postero central,

2:42

but here are examples of Anter central displacement,

2:46

postero central displacement,

2:48

and central displacement taken from an article

2:51

in the literature.

2:53

Another anomaly that we may see is

2:57

a ring light meniscus.

2:59

It looks like a discoid meniscus,

3:02

but there is an area deficient

3:04

of meniscal tissue present within it.

3:07

Some people classify this as a pattern of discoid meniscus.

3:13

This is infrequent, but it does produce diagnostic problems.

3:18

Just to show you an example, Evelyn Fazar uh,

3:21

sent me this case quite a while ago, and you look at this

3:25

and you can see that there is a normal appearing peripheral

3:29

portion of the meniscus

3:31

and there is a central piece of the meniscus

3:34

with a gap in between.

3:36

This is a ring light meniscus,

3:39

and we have seen a few examples in which this sort

3:42

of anomaly is also associated

3:45

with an anomalous anterior cruciate ligament arising from

3:50

the inner aspect of that ring light meniscus.

3:55

I'm just gonna talk briefly about meniscal movement. Okay?

4:00

Clearly, in fact, the meniscus may move slightly

4:03

during weightbearing,

4:04

but we look for meniscal extrusion as a sign of pathology.

4:11

It is important to remember

4:13

that the menisci belonged to the tibia.

4:17

So when we look for the alignment of the meniscus, we do,

4:20

we look through the relationship with the tibia

4:23

and not the femur on the medial side.

4:26

These line up

4:27

and any portion of the meniscus that is outside of

4:31

that line is abnormal.

4:33

On the lateral side, you may see very minimal, um,

4:37

a meniscal tissue, perhaps a one millimeter

4:41

or less outside of the lateral tibial plateau.

4:45

There are many, many causes of meniscal extrusion, right?

4:49

I've listed, uh, some of them here.

4:51

I'm showing you an example of severe synovitis associated

4:56

with uh, uh, meniscal tearing

4:58

and marked peripheral meniscal extrusion.

5:01

Whenever you see this, always check

5:03

to be sure you do not see an accompanying insufficiency

5:07

fracture in the ipsilateral compartment.

5:12

There are vacuum phenomena that can be seen in the knee.

5:17

This is a pathologic condition that can produce, uh,

5:21

confusion when you try

5:23

to judge the integrity of the meniscus.

5:25

This is intraluminal gas low signal

5:29

that could simulate meniscal pathology,

5:33

and this is gas within the meniscus itself.

5:36

Also, simulating meniscal pathology.

5:39

This is something that we see

5:41

with degenerative meniscal tears.

5:44

Another pathologic finding we can see is calcium

5:48

pyrophosphate dihydrate crystal deposition disease here,

5:52

I showed you this example before.

5:54

This can create diagnostic

5:56

Problems 'cause we often don't have conventional

5:59

radiographs when we interpret the MR images.

6:02

Here's an example of calcium pyrophosphate deposition

6:07

where the MR image does look like free edge tearing in gout.

6:12

The situation is different here.

6:14

The urate crystals typically are seen on the surface

6:18

of the meniscus.

6:20

This is known as icing.

6:22

The crystals typically are not as present

6:24

as much within the meniscus.

6:26

Now in gout, there are other tissues around the knee

6:29

that may be involved.

6:31

I just wanted to show you one of the characteristic

6:34

locations, involvement of the popple tendon.

6:37

This is what it looked like, arthroscopically,

6:40

and here in one of our cadavers

6:42

urate crystals along the course of the popple tendon.