0:00

Okay, our next meniscal focus

0:03

is what I call the lateral meniscus rule.

0:09

Now in order to illustrate what I mean by that,

0:11

I have to go back to my rudimentary drawing skills.

0:19

And I'm interested in discussing

0:22

the anterolateral meniscus rule,

0:24

which means there's a posterolateral meniscus rule.

0:27

But that's not the subject today.

0:30

It's the anterolateral rule.

0:32

So, we've got a very busy party

0:36

going on anteriorly.

0:38

We have,

0:40

as previously mentioned

0:41

in some of our discussions,

0:43

the transverse meniscal ligament of Winslow.

0:46

Which, by the way,

0:47

is not present in every individual, but in most,

0:50

it is.

0:51

The degree to which the transverse

0:54

meniscal ligament extends along the anterior horn

0:58

of the lateral meniscus varies,

1:01

but it has a much more complex attachment.

1:04

It has a slightly interdigitated attachment,

1:07

along with tissue that is made of capsule

1:11

and synovium.

1:12

And in order to illustrate that,

1:14

I have to make a much thinner line.

1:17

And I'll do that right now.

1:19

So, you're going to have quite

1:21

a bit of interdigitation

1:23

between the fascicles of the ligament

1:27

and the capsule in the synovium,

1:29

which I have drawn in green.

1:34

So if you're looking at a normal meniscus,

1:37

and let's do that.

1:39

Redraw our meniscus in cross-section

1:42

as if it's a sagittal view.

1:44

So, this is our sagittal view.

1:46

And it's a little thinner this time

1:48

because I didn't have time to thicken up the line.

1:50

Well, let me try it with a thin line.

1:57

So, there's your anterolateral meniscus.

1:59

And usually, the anterolateral meniscus is

2:01

not straight up and down.

2:03

It's sloped.

2:04

Sometimes it's even sloped this much.

2:06

I'll take out my eraser.

2:10

Oops. Didn't want to do that.

2:12

Here's my eraser.

2:15

So, it'll often look a little bit like this.

2:18

Then you have the transverse meniscal ligament

2:23

of Winslow, which is going to sit right here.

2:25

Should be in blue.

2:26

Let's make it blue.

2:30

And then, you're going to have

2:31

areas of interdigitation

2:34

which I will draw in green.

2:36

I'll make them a little thicker now

2:38

so that they're more easily seen.

2:40

You have these little areas of interdigitation.

2:42

Sometimes you have one dominant one,

2:44

sometimes you have a lot of little ones.

2:46

You will also have some interdigitation

2:49

that comes down from the top,

2:50

especially as you get close

2:52

to the root attachment.

2:55

So, if you have capsulosynovitis,

2:58

or capsulitis,

3:00

these green areas of interdigitation will become

3:05

more conspicuous, a little thicker,

3:07

and they'll swell.

3:09

And if they're pretty deep,

3:11

let's say this one was really deep.

3:13

You could easily go down the drain

3:16

and call it a cleavage tear.

3:20

So, what's a mother to do?

3:23

You've got interdigitation,

3:25

you've got the transverse meniscal

3:28

ligament of Winslow.

3:29

And to make matters even worse,

3:31

you also have the largest menisco synovial

3:34

recess of the knee, the anterior recess,

3:37

which comes out like this.

3:39

So if you have an effusion.

3:41

Very common for the effusion to hang right there.

3:44

So now another structure has been

3:47

lobbed into this inflamed knee.

3:50

Maybe some chondromylation in the neighborhood.

3:54

So here is an important lateral meniscus rule.

4:00

If you are imaging in the sagittal projection.

4:04

And you are unsure whether you have a tear or

4:08

whether you're looking at inflamed areas

4:10

of synovial attachment and ligamentous

4:14

interdigitation.

4:16

Almost never will the tear sit here at the root

4:20

and not propagate to the body horn junction.

4:23

So if after the second slice,

4:26

that signal suddenly and abruptly goes away,

4:30

it's either not a tear or it's not

4:33

a tear worth dealing with.

4:35

We're not talking about the root coming detached

4:39

and the meniscus floating away and the meniscus

4:41

twisting. Talk about it's in its normal position.

4:44

And you see either one or more

4:47

signals close to the midline.

4:52

Rule number two,

4:55

the lateral meniscus is a most favored nation.

4:58

Meniscus for meniscal pseudocysts

5:01

of meniscal origin.

5:02

More common lateral than medial.

5:05

More often painful lateral than medial.

5:08

More often smaller lateral than medial.

5:12

More often anterior lateral than medial.

5:16

So this is a good spot to get a perimeniscal

5:20

pseudocyst of meniscal origin.

5:22

What's not good is the tail.

5:25

The tail is going under the meniscus.

5:28

That's a meniscus synovial recess.

5:31

Or if it's under pressure and there's no fluid

5:34

in the joint, could be a ganglion.

5:36

Whereas a true meniscal pseudocyst

5:40

of meniscal origin.

5:42

Comes right out of the dead center of the

5:44

meniscus. So it'll look something like this.

5:47

It'll bisect it. I'll do it in pink.

5:50

So a true meniscus pseudocyst comes right out.

5:54

We'll overlay it right there.

5:56

That is what a meniscal pseudocyst

5:59

of meniscal origin should do.

6:02

The tail should go right down the middle.

6:04

Now should it come out the other side?

6:07

It'd be nice if it did,

6:08

but they don't all they can be true intraminiscal

6:13

tears and just blow out the peripheral

6:15

capsuler surface. How do you know?

6:18

Well,

6:19

because it goes in at least half

6:21

the depth of the meniscus.

6:23

It's a white line that communicates clearly with

6:27

the thermometer bulb of the pseudocyst

6:30

and it's right in the center.

6:32

How did it get there?

6:34

Usually there's an area of weakening so that there

6:36

is diffusion along the radial bundles of the

6:39

meniscus all the way out from the

6:42

inner third to the outer third.

6:44

Even though you might not see

6:45

the inner third component.

6:47

How do you deal with these ones

6:50

that are intraminiscal?

6:52

You may have to go from the outside,

6:54

take it out and then sew the

6:58

ones that communicate.

7:00

You go from the inside and sew them shut and

7:04

you leave the outside pseudocyst alone.

7:07

And it usually dries up on its own

7:09

unless it's inordinately large.

7:11

But the take home message,

7:13

the anterolateral rules are lots of

7:17

interdigitation along the anterolateral

7:21

deep horn and root,

7:23

both ligamentous and synovial interdigitation.

7:27

Unless it's on the third, 4th, 5th sagittal slice,

7:32

it's not going to be a cleavage tear here.

7:36

And fluid containing areas anterior to the lateral

7:41

meniscus are not of meniscal origin unless they

7:43

come right down the middle of the meniscus.