0:00

We're gonna finish up this particular lecture by trying

0:05

to tie together now a common pathway

0:09

that may explain the overlapping features

0:12

and the simultaneous occurrence

0:14

of more than one of these conditions.

0:17

Trans osteopenia, osteonecrosis

0:21

and subc chondral insufficiency fractures.

0:24

So bear with me a little bit

0:26

'cause I may be introducing a couple of terms

0:28

that you have not heard of before.

0:31

The initial stimulus that leads to transit, migratory

0:35

or non-migratory osteopenia, which is equivalent

0:39

to marrow edema or edema, like changes on mr.

0:43

This stimulus is not entirely clear.

0:47

We know there is a important relationship between the two,

0:51

the osteopenia and the appearance of edema

0:53

or edema, like changes on mr.

0:57

There is accumulating evidence that suggests

1:00

that the stimulus initiates a series of events, a cascade

1:04

of events, if you will, through a pathway

1:07

that involves this.

1:09

And up to about 10 years ago, I never heard of this

1:12

regional accelerator phenomenon.

1:15

Let's call it wrap.

1:17

When I learned about this through one article,

1:19

I did a literature search, this is from I think five

1:22

or 10 years ago, just to give you an idea of

1:25

how many articles I've used wrap or this particular term.

1:30

So it's something I should have known about

1:32

before wrap regional celebratory phenomenon.

1:38

A lot of these articles appear interestingly in the dental

1:41

literature related to the response

1:44

that occurs falling extraction of a tooth.

1:46

But let me explain it.

1:48

Wrap according to these articles is an SOS tissue reaction

1:53

to some noxious stimulus.

1:56

We haven't talked about the stimulus list,

1:58

but what it does is guarantee that there is a normal,

2:04

uh, result from a insult applied to the bone.

2:08

And it's one example, it is wrapped that leads

2:11

to callous formation

2:13

and bone union rather than non-union following a fracture.

2:17

So it appears to be a very important

2:20

SOS tissue reaction when you look at it in more detail.

2:24

It acts at a cellular level consisting

2:28

of a wandering team of osteoblasts and osteoclasts.

2:32

This is the BMU, the basic multicellular unit,

2:36

and it's that unit

2:38

and these cells that lead to coupled remodeling

2:42

of bone, which is coupled bone resorption

2:45

and bone formation closely coordinated.

2:49

So wrap is really a critical phenomenon

2:52

that you should know about.

2:54

Now let's go back to the stimulus.

2:56

There's a lot of evidence that suggests

2:58

That the stimulus for activating wrap is repetitive

3:03

loading and unloading of bone, that

3:06

that particular stimulus will get wrap moving.

3:10

Now this type of stimulus leads

3:13

to micro damage, right?

3:16

And eventually macro damage in the bone.

3:19

And there are many articles that have indicated

3:21

that the extent of damage is going

3:23

to depend on the magnitude of the load, the number rate,

3:27

frequency, duration, distribution,

3:30

and polarity of the loading cycles.

3:32

And of course, the quality or quantity of the involved bone.

3:38

Prolonged or exaggerated wrap leads

3:40

to an inflammatory response in bone

3:43

that increases the capillary bed.

3:46

It produces hyperemia, increases bone turnover

3:49

and produces marrow edema like changes.

3:52

And once you have the edema like changes,

3:55

you elevate the pressure within the involved bone marrow

4:00

hyperemia leads to loss of bone in the form

4:03

of various patterns of regional osteopenia.

4:07

Okay? So the regional osteopenia closely associated

4:10

with a marrow edema like abnormalities, rapid rap

4:14

and other unknown stimuli may also trigger

4:18

complex regional pain syndrome.

4:21

And it's been likened to other forms of regional osteopenia

4:24

as well and generalized uh, forms of osteopenia.

4:30

Now to this particular point, all

4:32

of these findings are reversible,

4:35

although in some person's additional irreversible

4:38

abnormalities may appear.

4:40

And what are those abnormalities?

4:42

The first can be a subc chondral insufficiency fracture

4:47

because indeed the osteopenia leads to weakened bone, right?

4:52

These insufficiency fractures are accompanied

4:55

by marrow edema, right?

4:57

And the marrow edema may actually be the cause

5:01

of the insufficiency fracture rather than the result of it.

5:06

Sub choral insufficiency fractures can lead to bone collapse

5:10

as well as focal regions of osteonecrosis,

5:14

although of course there are multiple other causes

5:17

of widespread and focal osteonecrosis.

5:20

These last findings are

5:23

but don't have to be irreversible.

5:25

So I've illustrated that

5:27

by showing the irreversible ones in dark green,

5:31

the subcon insufficiency fractures can in fact

5:34

be reversible.

5:36

So what I've tried to do in the very end of this is to kind

5:39

of show you a pathway that might explain the relationship

5:43

between these three things.

5:45

Trans osteopenia, osteonecrosis

5:48

and subc chondral insufficiency fractures.

5:51

They are distinct disorders,

5:53

but there may be a common pathway and that is why

5:57

although they may occur independently,

5:59

they can also occur together.

6:02

And that does in fact create a diagnostic dilemma

6:06

for radiologists.