0:00

So we'll discuss CMC injuries.

0:04

Here is a patient with post-traumatic wrist pain,

0:07

frontal projection, lateral projection.

0:11

So let's discuss the carpal metacarpal alignment.

0:14

So normally the carpal metacarpal joints have this zigzag

0:18

configuration, but maintain a parallelism between the

0:23

distal aspect of the carpus and the base of the metacarpals.

0:27

So the case that we reviewed shows

0:29

that there is offset here at the base of the fourth

0:32

or ring finger metacarpal,

0:35

and that there's loss of this parallelism of the zigzag

0:39

of the carpal metacarpal junction.

0:41

And those are the diagnostic features

0:43

for carpal metacarpal injury.

0:46

So the second through fifth carpal metacarpal joints,

0:49

that is the index.

0:51

Long middle ring,

0:53

and small fingers are well visualized on the PA radiograph.

0:57

The width of that joint is typically about

0:59

one to two millimeters.

1:01

The opposing surfaces should maintain this parallelism.

1:05

It can be technique related,

1:07

and that's why we talked about having the hand flat on the

1:10

plate with particular positioning for wrist

1:12

and hand imaging on the lateral.

1:15

It can look at the longitudinal axis of the shafts

1:17

and make sure that they're parallel

1:19

if there's any concern or questions.

1:21

Sometimes the oblique projections can

1:23

have additive information.

1:25

And so if we go back to our original projections

1:28

and then add the oblique, we can see

1:31

that there's offset here at the base

1:33

of the ring finger metacarpal on MRI.

1:37

There's a bone marrow edema pattern and a fracture line,

1:41

and this represents carpal metacarpal injury.

1:44

These are uncommon lesions that can occur as fractures and

1:47

or dislocations, typically multiple more likely than single.

1:52

The fifth or small finger metacarpal is the most common.

1:56

The extensor carpal narrows may distracted at the base

1:59

of the fifth metacarpal as it attaches there.

2:03

Majority of them have a dorsal dislocation component

2:07

rather than lar, so about two thirds dorsal

2:10

and one third volar.

2:12

The mechanism is unknown,

2:13

but likely related to a direct blow

2:15

where you apply longitudinal force down the long axis

2:19

of the metacarpals.

2:21

The diagnosis is often delayed

2:23

because while they present with soft tissue swelling,

2:25

the radiographic findings can be subtle as shown here

2:29

and sometimes overlooked,

2:31

but with careful scrutiny

2:32

of the carpal metacarpal articulation, it won't be missed.

CMC Injuries Summary

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