0:00

Okay, so let's go ahead

0:02

and get started with the, uh, next, uh, topic,

0:04

which you can see on the slide.

0:07

We're gonna talk about osteonecrosis, transient osteopenia

0:12

and subc chondral insufficiency fractures,

0:14

and we'll address both dogma and dilemma.

0:18

And I think it's important that we discuss all three

0:21

of these particular topics together

0:24

because there are similar

0:26

and sometimes overlapping imaging features in these three

0:30

disorders and one may be followed by another

0:34

or they more than one may occur simultaneously.

0:38

So I'm gonna try to show you the relationship

0:41

between these three disorders

0:44

and propose a pathogenic pathway, uh,

0:47

that at least I've come up

0:49

to make me think why one may become another in terms

0:52

of, uh, imaging.

0:54

So transo, osteopenia, osteonecrosis,

0:58

and subc chondral insufficiency fractures.

1:02

So let's begin with osteonecrosis

1:04

and let's address the terminology that is generally used for

1:09

osteonecrosis, which varies according

1:11

to the site of abnormality.

1:13

When we deal with involvement of the end of a long bone,

1:17

typically we talk about avascular necrosis

1:20

or ischemic necrosis,

1:22

or perhaps we shorten it to the term osteonecrosis.

1:26

When we talk about involvement of a med, a medullary portion

1:30

of a long bone or even a short tubular bone involving the

1:35

metaphysis or diaphysis.

1:36

The proper term to use for that is bone infarct

1:40

or infarction.

1:42

Most of what I will address today will be involvement at the

1:46

end of a bone, but bone infarct also will enter into

1:49

the differential.

1:51

And you can see the classic appearance here, the

1:54

vascular necrosis involving the femoral head

1:57

with a crescent fracture appearing as a radiolucent curve,

2:01

linear line, and a bone infarct involving the distal

2:05

aspect of the femur.

2:08

Now, when we talk about bone necrosis, be it, uh, areas

2:13

of, uh, involvement of an epiphysis

2:16

or bone infarction, there are a number of causes,

2:19

and I've listed some of them,

2:20

certainly not all of them here.

2:23

I wanted to emphasize the third one, vasculitis,

2:26

in particular, the occurrence of necrotic bone in cases

2:31

of systemic lupus erythema ptosis.

2:34

And the reason I, I do this is I've been so impressed

2:37

that when you are dealing with widespread

2:40

osteonecrosis involving multiple bones, I always,

2:45

at least myself think first of lupus.

2:48

It's fairly frequent in lupus,

2:50

and the literature would suggest 12 to 15%

2:54

of lupus patients may develop osteonecrosis.

2:57

But it's the multiple sites of involvement

2:59

that have really impressed me.

3:01

Typically, of course, we think of the femoral head

3:04

and we think of the bones about the knee,

3:06

especially the femur or tibia of rarely the patella.

3:11

But it can involve small bones.

3:13

And I show you an example here

3:16

where we have widespread necrosis, both bone infarcts

3:20

and osteonecrosis involving multiple bones about the ankle

3:24

and following amputation there, the image shows you

3:28

what the necrosis involving the ALI look like.

3:32

The major risk factor in SLE is the corticosteroid therapy.

3:37

It's the combination of vasculitis

3:40

and corticosteroid therapy that can lead

3:43

to this particular complication.

3:46

The larger the doses, the longer duration

3:49

of corticosteroid therapy, those are factors that will

3:52

influence the, uh, appearance of, uh, osteonecrosis.

3:58

Now, there are a lot of reasons, uh, for why

4:02

convex surfaces such as the femoral head, humeral head,

4:05

and condyles and lunate are involved more commonly than

4:09

concave surfaces.

4:10

But I wanted to use these radiographs showing you a convex

4:14

surface and a concave surface

4:16

to point out one particular feature

4:18

that may not be well known to you.

4:21

When you look at the trabecular chambers, that is the,

4:25

the spaces between all the trabecula you can appreciate.

4:28

They're much smaller on the convex aspect

4:32

of a joint than on the concave.

4:35

And it suggested

4:36

because of that, that there may be more elevated

4:39

intra chamber pressure, which can pro promote the ex egress

4:44

of, uh, of fat from vessels

4:46

and can lead to compression of, of blood vessels.

4:50

So the convex surfaces are prone to develop,

4:54

uh, osteonecrosis.

4:56

The prototype, of course, is the femoral head.

4:59

So I thought I would give you, uh, start with that.

5:02

And here we can see a pathologic picture

5:06

of a femoral head involved in osteonecrosis.

5:09

Here's my drawing and here's a specimen radiogram,

5:12

and I think of this as a zonal phenomenon

5:15

with five particular zones.

5:18

I've labeled them with circles of different cos.

5:21

The first zone is the white zone,

5:24

and that's the articular cartilage.

5:26

And as you know, the cartilage derives its nutrition from

5:30

the synovial fluid.

5:32

So it's remarkable that you can have widespread

5:35

osteonecrosis involving the femoral head,

5:38

and yet the cartilage

5:39

and hence the joint space, is maintained.

5:43

The green area, this area, of course, is the necrotic bone.

5:47

And within it, the red area is showing you the classic

5:51

crescent fracture,

5:52

and I'll talk more about

5:53

that in a little while surrounding the area

5:56

Of necrosis in light green

5:58

and in gray is an area known as the reactive interface.

6:03

The green, uh, light green circle is the granulation tissue,

6:07

which is radiolucent on the specimen radiograph

6:10

and surrounding it, the dark gray is the sclerotic region

6:15

and together to make up the reactive interface.

6:19

The reactive interface is certainly something we look for

6:22

with imaging studies.

6:24

And I thought I'd show you an example here

6:27

where the reactive interface is very, very complicated

6:30

because it can be multiple.

6:32

And here you can appreciate multiple reactive interfaces

6:36

showing you some bright signal.

6:39

Okay, and entrap fat, which is very, very characteristic

6:43

of osteonecrosis in some cases, owing to double interfaces,

6:48

the line may actually extend across the femoral neck

6:51

and may simulate, may simulate the appearance of a fracture

6:56

of the femoral neck.

6:58

Now, the general rule about the crescent sign,

7:01

which is a fracture through the necrotic bone,

7:04

it can occur either beneath the subcon bone plate,

7:08

which is the compact bone that lines the surface

7:12

of the femoral head, or it can go extend into the cartilage.

7:16

And once it extends into the cartilage, it can lead to

7:21

fragmentation of the cartilage surface.

7:24

And I wanted to emphasize that particular point

7:27

because we're gonna talk later about subc chondral

7:30

insufficiency fractures where the location

7:33

of the fracture line is a little bit different.

7:36

Here's a nice example, uh, a specimen showing you a

7:42

pressing fracture through necrotic bone

7:44

and you can appreciate the violation of the surface

7:48

of the femoral head and even displacement of the, uh, bone

7:52

and cartilage fragment.

7:56

Now, some people have suggested we can use imaging,

7:58

particularly Mr imaging

8:00

and come up with an idea about the general prognosis

8:04

of osteonecrosis involving the femoral head.

8:07

That is whether or not collapse is going to occur.

8:11

And the way this is generally done is you come up

8:14

with a combined necrotic angle based upon two measurements.

8:18

One is done in the coronal plane and a mid coronal image,

8:22

and one is done in a sagittal image.

8:25

And you try to decide on the degree, the, the angle

8:29

of involvement on those two images,

8:31

and then you add those up together

8:33

and you end up with this sort of risk

8:36

or subsequent collapse of the, uh, surface

8:40

of the femoral head.

8:41

Now, I don't think we're using this

8:43

and I don't think it's, uh, that reliable,

8:47

although obviously the wider the osteonecrosis, uh,

8:50

the more extensive it is, the more likely the bone collapse.

8:53

But it's been pointed out

8:55

that it also depends on whether the lesion

8:58

is superficial or deep.

9:00

You can have a small region of osteonecrosis located deeper

9:05

within the, uh, femoral head,

9:07

and when you draw your angle,

9:08

you're gonna get a very large angle.

9:10

So some people do not think this particular method

9:14

for determine the prognosis with regard to collapse

9:18

of the femoral head is very valuable.

9:22

Now, here is an article that I want to, uh, concentrate on

9:25

for a moment and we're gonna look at some

9:27

of the key articles, uh, uh, through the years that kind

9:31

of introduced the controversy of the relationship

9:35

between osteonecrosis and insufficiency fractures.

9:39

It was this article that came out of the hospital

9:42

for special surgery in 1999

9:45

where they did a retrospective review of a large number

9:48

of surgically removed femoral heads in elderly persons.

9:53

And what they found is

9:54

that insufficiency fractures were diagnosed in 10 femoral

9:58

heads that had an original histologic diagnosis

10:02

of osteonecrosis.

10:04

So now we're seeing osteonecrosis

10:06

of the femoral head simulated by insufficiency fractures.

10:10

These two pictures taken from that particular article,

10:15

I want you to note the name Yamamoto

10:17

because he is a champion

10:19

of insufficiency fractures occurring in subc chondral bone.

10:23

And you'll see that in several of his articles later on.