0:00

There was another entity

0:02

that was described initially in 1968.

0:06

Okay. And this was called Spontaneous Osteonecrosis

0:10

of the Knee, often abbreviated sun, SONK.

0:15

I believe this article originated in the

0:17

Scandinavia countries.

0:18

And what it was was a description of a painful,

0:22

lucid lesion seen on conventional radiographs,

0:26

typically in older persons,

0:28

involving most commonly the medial femoral condyle

0:32

that could subsequently lead to collapse

0:35

of the surface of the condyle.

0:38

And when indeed histology was, uh,

0:42

investigated in such cases it was interpreted as evidence

0:46

of osteonecrosis.

0:48

And hence the term sunk spontaneous osteonecrosis about the

0:52

knee was, uh, generated.

0:55

Just to give you a few words first, about

0:58

what are the initial clinical

1:00

and radiographic descriptions of what was called s

1:04

it was also called All Backs disease.

1:06

As he was one of the early investigators,

1:08

it was seen in older persons, more often a woman than a man.

1:12

It led to pain, a abrupt onset of pain

1:16

and said to be worse at night.

1:18

The classic location in the knee shown here was the medial

1:22

femoral condyle, the weightbearing surface.

1:25

Less commonly it was the lateral femoral condyle,

1:28

even less commonly the medial tibial plateau.

1:31

And rarely it was the lateral tibial plateau.

1:35

And what was documented and emphasized was the collapse

1:39

and flattening of the bone surface that could occur.

1:42

Hence the appearance resembled that of osteonecrosis.

1:47

Then along came Yamamoto,

1:49

and again with his friend Peter Bulla,

1:52

who was a pathologist again from the

1:54

hospital for special surgery.

1:55

And they said, wait a minute.

1:57

If you look at cases of sunk, there's histologic evidence

2:01

of insufficiency fractures,

2:03

and the necrosis may be a secondary phenomenon.

2:07

This was one of the early articles that came 2000,

2:11

the year 2000, describing 14 patients

2:14

with s They were treated operatively

2:17

and when they looked at the histology,

2:19

they believed insufficiency fractures were occurring

2:23

and there might be small areas of osteonecrosis

2:25

that they believed were secondary.

2:28

So here we had the relationship again, of osteonecrosis

2:32

in the term or in the appearance that turned out

2:35

to be insufficiency fractures.

2:38

So just to show you a couple of examples of

2:41

what these insufficiency fractures might look like,

2:44

here's an example of one occurring in the subcon bone,

2:49

and you can appreciate

2:50

that it is separated from the subcon bone plate,

2:53

which is the, uh, covering of compact bone on the condyle.

2:59

You can see also the degree

3:00

of marrow edema may be quite large when compared to the size

3:05

of the insufficiency fracture.

3:07

Here's another one, and in this one again,

3:09

the medial femoral condyle.

3:12

Again, you can see this a larger insufficiency fracture

3:16

separated from the subc bone plate.

3:19

So these fractures appear to begin in the subchondral bone,

3:22

but what can occur over a period of time, they can merge

3:26

with the subcon bone plate.

3:28

So here is an important point diagnostically,

3:31

you may not see a separate insufficiency fracture line,

3:36

but you may see focal thickening

3:39

of the subc chondral bone plate as the insufficiency

3:44

fracture originally located in the subc chondral bone kind

3:48

of merges with the subc chondral bone plate.

3:52

So focal thickening

3:53

of the subc chondral bone plate can be an important finding

3:57

of an insufficiency fracture.

3:59

There was a beautiful exhibit in at the RSNA now I guess,

4:04

uh, 10 years ago that compared the location

4:09

of the subc chondral insufficiency fracture

4:12

with the location of a fracture through necrotic bone.

4:16

And it was emphasized that

4:18

with subc chondral insufficiency fractures shown in these

4:21

pictures, they initially occur

4:23

below the subc chondral bone plate, but may merge with it.

4:27

When we go back to the crescent sign

4:29

and the fracture, the pathologic fracture

4:32

through necrotic bone, it can occur within, shown here

4:37

or below the subc chondral bone plate.

4:40

And as I've already shown, may lead to fracture

4:44

of the cartilage itself.

4:46

So there's a slight difference in the location,

4:49

but clearly a diagnostic problems sometimes separating this

4:54

from a crescent sign in osteonecrosis,

4:58

when we learned about insufficiency fractures occurring

5:01

and sunk being the primary abnormality,

5:04

it was not surprising then that lots

5:07

of articles appeared about associated

5:10

ipsilateral meniscal abnormalities.

5:13

This was pointed out that it occurred frequently in patients

5:17

who had sunk, okay.

5:19

They sunk being the old term more often on the medial side

5:23

than the lateral side,

5:24

particularly involving the posterior horn

5:27

and particularly with radial tears of the posterior horn

5:31

of the medial meniscus or posterior root ligament.

5:35

There were other associated meniscal things such

5:39

as previous meniscal surgery, meniscal extrusion

5:42

and loss of articular cartilage that could fact lead

5:46

to these insufficiency fractures.

5:49

To show you a nice example,

5:50

and I'll talk more about this later on in the course when I

5:54

talk about the knee meniscus, but here is

5:56

A posterior root ligament tear of the medial meniscus

6:00

and you can see again an insufficiency fracture

6:04

involving the medial femoral condyle merging

6:08

with the subcon bone plate.

6:11

Another example here where the images on your left

6:15

show early marrow edema, this,

6:18

these are changes occurring in the subc condral bone

6:21

with a posterior root ligament tear

6:23

and meniscal extrusion two months later.

6:27

The classic features of what originally was called sock,

6:31

so we're dealing now

6:32

and it's a, a wide, uh, belief

6:35

that insufficiency fractures were the cause of s sun.

6:40

Now, I also learned about this late in life

6:42

because I can look at this particular article

6:44

that we wrote in 1991 where we were talking about patients

6:48

who had prior arthroscopic surgery, in most cases, partial

6:54

meniscectomies, and we saw these changes occurring in the

6:57

subchondral bone and we said, well,

7:00

this was osteonecrosis occurring in the bone, um, secondary

7:05

to the meniscal surgery.

7:06

We now know that these relate to insufficiency fractures,

7:11

so perhaps a better term for what was originally called ssc,

7:15

a spontaneous insufficiency fracture,

7:17

although it's not really spontaneous sif about the knee

7:21

related to prior meniscal surgery.

7:25

And there's another entity that you may know about.

7:27

It's a, uh, important radiographic sign,

7:32

and that was the sign of a collapsed vertebral body

7:36

with a fracture in that fracture often containing gas.

7:40

This was known as the vacuum vertebral body,

7:43

and it was felt initially to be related to osteo necrosis.

7:48

That's an important sign by the way,

7:50

because if you're the observer and you come in

7:52

and you have a patient with a collapsed vertebral body,

7:56

you have a long list of diagnostic possibilities

7:58

that top the list, things sinister like infection and tumor,

8:02

but if you could find the vacuum, okay,

8:06

within the collapse vertebral body, often near the surface,

8:10

you can see a little bit of vertebral body bone here.

8:14

If you could find that you could generally eliminate the

8:17

diagnosis of malignancy or infection,

8:21

and it was believed to be very, very similar

8:24

to the appearance that we see with osteonecrosis

8:28

and a crescent fracture.

8:30

Many of those patients, in fact, were on steroids,

8:32

but I would suggest that this too

8:35

may be an insufficiency fracture rather than

8:38

initial osteonecrosis.

8:40

So this would be somewhat spontaneous insufficiency,

8:44

fracture of a vertebral body.

8:46

This is also linked to another phenomenon, ALS phenomenon

8:50

that I won't go into uh, detail today.

8:53

So this again, likely an insufficiency fracture occurring in

8:57

a weakened vertebral body leading perhaps

9:00

to secondary osteo necrosis.