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If we're gonna finish up now in the last five

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or seven minutes by proving as we talk about trauma,

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that fat is your friend, the identification

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of extruded marrow fat can provide critical information

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regarding the presence

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and beyond that the pattern of bone injury.

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So let me show you some examples.

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The first of these is our old friend lipo.

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He arthrosis where we have both fat

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and blood in the joint.

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The presence of a lipo, he arthrosis is very,

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very strong evidence, not certain evidence, strong evidence

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that a fracture is present

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and the fracture okay, has released

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fat into the joint cavity.

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Now we all recognize this.

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There are two classic patterns that we see.

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The first of these are fluid levels shown beautifully here.

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It's an old image, but I like it.

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A transverse or axial image showing you three layers

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and two fluid levels.

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The top layer fat signal intensity, identical

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to marrow fat on a fat suppressed image,

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the middle layer bright the serum,

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and the lower layer intermediate signal

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representing the cellular or hematocrit effect of the blood.

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That classic fluid levels.

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And the other one, some people think hyper acutely

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bubbles of fat.

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Often these will rise to the surface

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of the he orthosis, as in this case.

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Sometimes they appear deeper down little globules

1:45

of fat embedded within blood clots.

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But this is a pattern easy to miss,

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but something you should look for a lipo he arthrosis,

1:54

or perhaps both.

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Here we can see both levels shown by the yellow

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arrows and a globulin fat shown by the white arrows.

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Both are present. Now,

2:09

something I learned relatively late in life

2:12

that when you look closely at these fluid levels

2:17

associated with a lipo, he arthrosis

2:20

or even a he arthrosis,

2:22

they may not always be gravity dependent.

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I always thought they were,

2:27

and they were straight across parallel of course

2:29

to the the gravity.

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But basically the, the way they appear relates

2:36

to complex factors including the viscosity of the contents

2:41

and the patient positioning prior to imaging.

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So here's an example with an obliquely oriented level.

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I just learned that recently.

2:51

Another thing you may see fat is your friend

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following an injury, you may get subperiosteal

2:59

Extrusion of fat. So

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here I show that diagrammatically

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and you can uh, see that the periosteum,

3:05

this is in the immature skeleton is lifted

3:08

off, but still attached.

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So you might imagine that that fat would collect

3:13

beneath the elevated periosteum.

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We see this particularly in the immature skeleton in

3:19

children, particularly involving fractures

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of the distal radius,

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especially involving the dorsal surface.

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Here's what it looks like, an old case,

3:29

but you can see two small collections of fat.

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And the reason I wanted to show you this, that if you were

3:36

to then image this particular child later on,

3:40

you might see something like this

3:43

because now the elevated periosteum has formed bone

3:47

and as it formed bone, it left behind those little globules

3:51

of fat seen radiographically and on the mr.

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And if you don't know this, you may say, boy,

3:58

this is a great case of two osteo

4:01

osteos involving the distal radius.

4:04

It's entrapped fat related to this particular phenomenon.

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And another collection

4:11

of fat you may see is within tendon sheets.

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We see this particularly in the hand, in the wrist,

4:18

in the ankle and foot generally related to a fracture

4:22

of a nearby bone.

4:24

I show you a beautiful example

4:25

of a fracture involving the distal radius with release

4:29

of fat entra.

4:30

Now within the second dorsal extensor compartment,

4:34

you can see beautifully here the fat on these MR images.

4:39

So Tino synovial extrusion of fat.