0:00

<v ->Well, let's turn our attention now

0:02

to Spontaneous Osteonecrosis of the Knee, SONK.

0:07

I think everybody listening to me today

0:10

and listening to Abdalla certainly have heard of SONK.

0:14

So let's go back to the initial article.

0:18

The initial article on SONK

0:20

I believe came from Scandinavia in 1968,

0:24

a long time ago.

0:26

And it was a description

0:27

of a characteristic painful radiolucent lesion

0:32

observed in knees in a number of patients,

0:35

typically over the age of 60,

0:38

that might progress to collapse.

0:41

And you can see for example, the pictures in their article

0:45

with progressive collapse of the medial femoral condyle.

0:50

These were studied scintigraphically

0:53

and were studied histologically

0:55

and the interpretation of the histology was osteonecrosis.

1:01

So this is how the, the term SONK began.

1:05

Now, when later on in 1978 and another description

1:13

of Spontaneous Osteonecrosis of the Knee

1:18

this description here written by Ahuja and colleagues

1:23

in New York.

1:26

They confirmed localized osteonecrosis

1:29

in the subchondral bone of the medial femoral condyle

1:34

in 67% of knees in a number of patients

1:39

who had the appearance of SONK.

1:42

So right away from the initial article and from this article

1:46

no argument, we are dealing with osteonecrosis of bone.

1:53

I learned about it

1:54

in all the clinical and radiographic features.

1:57

So at this point, let me remind you what they are.

2:00

The predominant involvement is of the media femoral condyle,

2:05

less commonly the lateral femoral condyle

2:08

less commonly than that, the medial tibial plateau

2:13

and rarely the lateral tibial plateau.

2:18

We saw this in elderly persons more often a woman.

2:23

They presented with pain.

2:25

They remembered the month, the day, the hour the minute

2:30

that the pain began.

2:32

They could remember it precisely,

2:34

typically again of the medial femoral condyle.

2:38

And the abnormalities that we would see included

2:41

depression of the subchondral bone plate

2:44

and fragmentation that might progress

2:47

from minor irregularity to frank collapse.

2:52

Now, a very important article appeared about that time.

2:57

This is in 1998,

3:00

written by a group from Belgium that often do terrific work.

3:04

And they said, you know, we're looking

3:07

at these patients who have SONK

3:09

and we're trying to decide,

3:11

is this gonna go on to collapse,

3:14

irreversible, meaning osteonecrosis

3:17

or this not gonna be irreversible, but actually reversible.

3:23

And so they studied the value of three particular signs

3:27

in trying to decide

3:29

whether the abnormality of the femoral condyle

3:32

was related to osteonecrosis and would progress,

3:36

or whether in fact it related to something else.

3:40

Now, they didn't define what that something else was.

3:44

And what they found was that the irreversible lesions

3:48

had a band of low signal that was larger and thicker.

3:54

And most importantly

3:56

there were surface irregularity of the condyle.

4:00

So when they saw this prominent band

4:03

and particularly surface irregularity

4:07

they said it was irreversible and likely in fact

4:11

related to Avascular Necrosis.

4:14

The third finding which looked like a fracture line

4:17

labeled number B here

4:20

was not helpful in deciding

4:22

whether or not this was reversible or irreversible.

4:27

So they were uncertain when they saw that particular line

4:31

especially when it was near the subchondral bone plate.

4:36

Now, this is important article

4:38

because in fact I think these observers

4:42

were trying to figure out what was osteonecrosis here

4:46

and what might be something else.

4:50

So you look at an example like this, and you would say,

4:53

here there's no contour abnormality,

4:56

there's marrow edema,

4:57

there's a band of thickness,

4:59

there's even a linear component above it

5:02

but this certainly could be reversible.

5:06

It doesn't show the bone collapse

5:09

and the area of low signal is not large enough.

5:13

Now along comes Yamamoto again, that's that same name.

5:19

Here he is working with Peter Bullough

5:21

a very famous Pathologist

5:22

at the Hospital for Special Surgery.

5:26

And here is the first description of histologic evidence

5:30

of an insufficiency fracture

5:33

in cases of SONK

5:35

although there might be small areas of osteonecrosis.

5:39

They described that in 14 patients with SONK

5:43

and identified insufficiency fractures.

5:46

So here again, now

5:48

something that had been diagnosed as osteonecrosis

5:52

but now was regarded as an insufficiency fracture.

5:57

And as soon as that article appeared,

6:00

hundreds of articles appeared

6:02

suggesting that Spontaneous Osteonecrosis about the Knee

6:07

related to an insufficiency fracture.

6:11

Here, I show you classic examples.

6:13

Medial femoral condyle the arrow pointing

6:17

to an insufficiency fracture in the subchondral bone.

6:21

Another example of medial femoral condyle

6:25

with one or more insufficiency fractures

6:28

in the subchondral bone.

6:31

A third example, and here perhaps irreversible

6:35

because it appears to be irregularity

6:38

of the subchondral bone plate.

6:41

An example in the medial tibial plateau

6:44

of fracture line

6:46

this should be irreversible because

6:48

of the depression of the subchondral bone plate.

6:53

What became apparent also is that

6:55

not only were these insufficiency fractures

7:01

but that they had a high association

7:04

with meniscal abnormalities

7:07

and the type of meniscal abnormalities varied tremendously.

7:11

But as you can see information taken from this article

7:15

in the American Journal of Sports Medicine,

7:18

75% to 90% frequency of meniscal tears and knees

7:25

they were calling it SONK,

7:27

but we're talking about insufficiency fractures,

7:30

particularly on the medial side,

7:32

especially involving the posterior horn

7:35

particularly with radial tears

7:38

and root ligament abnormalities

7:41

also associated with peripheral meniscal extrusion

7:45

prior meniscal surgery and loss of articular cartilage.

7:52

So the meniscus is a cushion.

7:55

If you do, if you have a bad cushion or no cushion

7:58

you've done a cushion ectomy

8:01

then indeed more stress

8:03

placed upon the bone in that compartment

8:05

and an insufficiency fracture might develop.

8:09

And a lot of the ones that we see in our practice

8:12

this one given to me by Marcello

8:14

but we see this relate to problems right back here.

8:19

This is the posterior horn of the medial meniscus.

8:22

Here's the posterior cruciate ligament.

8:24

I've always told my fellows

8:26

the most important half image

8:29

of a knee MRI examination is this half image.

8:35

A coronal image showing you the inner margin

8:38

of the posterior horn of the medial meniscus.

8:42

Radial tears of the meniscus

8:44

and posterior root ligament problems occur here.

8:48

They're both associated with peripheral extrusion

8:51

of the body of the meniscus,

8:54

bowing of an edema about the medial collateral ligament

8:58

and insufficiency fractures here with thickening

9:03

and irregularity of the subchondral bone plate.

9:07

Here's another one.

9:08

I think I showed this earlier in the course.

9:11

Marrow edema, stress related, a radial tear

9:15

or a posterior root ligament evulsion peripheral extrusion.

9:19

Two months later, classic SONK

9:23

related to an insufficiency fracture

9:26

of that medial femoral condyle.