0:01

Welcome to MRI Online's Vignette

0:03

Coronal Anatomy Variants.

0:06

Variants is the relationship

0:08

between the ulna and the radius.

0:13

It should be pretty congruent,

0:15

although MR is a static image.

0:17

Whereas many hand surgeons will get in the

0:19

office a radial deviation view, an ulnar

0:22

deviation, X-ray view, and a clenched fist view.

0:26

So they'll see some dynamic changes that

0:28

you might not appreciate on a static MRI.

0:32

So, when we're describing this relationship

0:35

between these two, we refer to it as

0:37

variance posture, to temper the language

0:41

that our hand surgery colleagues use.

0:45

We're interested in having this relationship

0:47

congruent, and sometimes, I'm gonna try to draw here

0:50

a little bit for you, the ulna will, even in the

0:53

static projection, be distal to the radius.

0:58

So this distality, it's about 8 millimeters.

1:01

So this distance would be about 8 millimeters.

1:05

Would give us some pause and some concern about

1:09

the sequela of positive ulnar variance posture.

1:13

And that sequela would be

1:14

ulno-lunate abutment syndrome.

1:18

So what would we be concerned about?

1:20

We'd be concerned about the ulna

1:22

pistoning into the base of the lunate.

1:25

If the ulna is positioned in a more distal variance.

1:29

And when it pistons, it will thin

1:31

the triangular fibrocartilage.

1:33

It will erode the ulnar base of the

1:36

lunate, not over here, over here.

1:39

And it will erode the hyaline membrane.

1:42

Cartilage of the ulna.

1:43

Not in the fovea, but over here,

1:45

more towards the radial side.

1:47

Do not confuse this thin, whitish, brightish

1:51

area as an erosion, or a defect, or a TFC tear.

1:56

That is the normal hyaline cartilage of the radius.

2:01

And that is an attachment site for the triangular

2:05

fibrocartilage to be discussed a little bit later.

2:08

So what about negative ulnar variance?

2:10

Negative ulnar variance would be the

2:13

situation where the ulna is positioned

2:16

proximal to the distal aspect of the radius.

2:23

Now this can happen after a fracture,

2:25

let's say an ulnar fracture.

2:27

Or you can have positive variance

2:28

after a fracture as well.

2:30

But we're talking ulnar, negative ulnar variance now.

2:33

And once again, this separation distance

2:35

would be about 8 millimeters or greater.

2:39

That can be normal, by the way.

2:41

But we are looking for the secondary

2:43

changes of negative ulnar variance posture.

2:46

And what do patients get with

2:48

negative ulnar variance posture?

2:50

They get, or they have a higher risk for,

2:54

lunatonecrosis, also known as Kienböck's disease,

2:58

which we'll discuss as a separate vignette,

3:01

and its etiology, which is vascular in nature.

3:04

Another problem that they get with negative

3:06

ulnar variance posture is swelling of the ulno

3:10

meniscus homolog in this area, swelling of

3:14

the styloid recess, and injuries or tears

3:18

or subluxations of the extensor carpi ulnaris.

3:21

But that is a story for another day.

3:24

That is a summary of variance posture, positive

3:29

variance leading to ulno lunate abutment,

3:32

and negative variance producing a higher risk

3:34

for Kienböck's disease and extensor carpi ulnaris

3:38

disease along with its surrounding structures.

3:41

Let's move on.