0:00

I'd like to scroll the sagittal projection

0:03

and have you focus for a moment on the

0:05

relationship of the lunate to the capitate and

0:09

the radius and talk not so much about rotation.

0:13

In other words, ventral or palmar facing

0:16

lunate, thissy, or dorsal facing lunate, so

0:20

called dissy, but rather the position of the

0:24

lunate relative to these other structures.

0:27

Now they should line up so that the metacarpal, which

0:31

you see right here, the metacarpal, and the capitate,

0:37

and the lunate, and the radius should all be collinear.

0:44

In other words, they should line up in a straight line.

0:48

Now what happens when they're not collinear?

0:52

When they're not collinear, there's instability.

0:53

We've already talked about rotation.

0:56

But in perilunate and lunate dislocations, unlike this

1:00

situation, which is a different type of instability,

1:03

more chronic, the lunate not only will rotate,

1:08

but it'll spit out towards the palm or surface.

1:11

So the lunate is more dorsally positioned.

1:14

It's not collinear, but it's in

1:16

the dorsal aspect of the line.

1:19

Whereas in patients with perilunate and lunate

1:22

dislocations, the lunate will be ventral facing,

1:26

but it'll also be spit this way, towards the east

1:28

coast, towards the palmar aspect of the wrist.

1:34

Let's have a look on a diagram

1:35

which makes it pretty simple.

1:38

We have linearity on this normal image between the

1:42

third metacarpal, the capitate, and the lunate.

1:44

I'm not a very good drawer.

1:46

In a perilunate dislocation, the

1:49

lunate and the radius remain collinear.

1:53

The capitate sits posterior, but

1:56

this relationship is maintained.

2:00

The lunate may or may not be ventral facing.

2:03

In this case, maybe just a hair.

2:06

In a midcarpal subluxation or dislocation, the

2:11

capitate is back a bit, but the lunate, which is

2:14

now facing the palmar surface, ventral facing

2:19

lunate, is also displaced ventrally, or palmarly,

2:24

unlike our clinical case, which we showed on MRI,

2:27

where the lunate was more dorsally positioned.

2:29

This is a midcarpal dislocation.

2:33

And then finally, in a true lunate dislocation,

2:36

the lunate is now not only ventral facing, but it's

2:39

also dislocated or spit out into the palmar space.

2:45

So these are four important variations.

2:48

Normal collinearity, perilunate dislocation,

2:52

lunate collinear with a radius, maybe a little

2:56

tilted, capitate back, midcarpal dislocation,

2:59

lunate is subluxed, capitate back, ventral facing,

3:06

true lunate dislocation, lunate subluxed and

3:10

dislocated, palmarly, ventral facing, capitate,

3:15

not displaced, now collinear with the radius.

3:21

That concludes our discussion of carpal instability.