0:01

This was a 27 year old, pretty young guy,

0:04

and he had this profound thumb flexion weakness,

0:07

really this inability to flex his thumb. Um, he was an avid weightlifter,

0:12

but really had no other, uh,

0:14

medical history and nothing else that was too significant to this case. So, uh,

0:19

a few axial sequences, uh, just going from proximal to distal,

0:26

and then one more scroll through from distal to proximal.

0:34

And then I think I've got one more plane here.

0:39

Oh, this was just a kind of zoomed up, um,

0:42

a thinner slice and smaller field of view

0:49

sequence as well. Okay.

0:53

So for our next polling question,

0:57

the distribution of the muscle abnormality in this particular case

1:02

suggests that which nerve is involved,

1:06

which nerve is involved in this case. All right, perfect.

1:12

This is an anterior interosseous nerve pattern. Very good.

1:16

So let's talk a little bit about anterior interosseous nerve syndrome or

1:20

entrapment. Uh, remember this is the deep branch of the median nerve. Uh,

1:24

it can be traumatically injured, can be compressed from, uh, tumors or other,

1:28

uh, lesions in the forearm.

1:31

And patients present clinically with this inability to form kind of the a o K

1:35

sign. Uh, they call this the circle sign, uh,

1:37

and patients will have this weakness of the thumb flexion.

1:41

So this patient presented classically, there's sometimes in the clinical, um,

1:46

presentation, these cases are very evident.

1:49

And so then it's the radiologist's job to make sure there's not something else

1:52

going on. Because this patient was so young, uh,

1:55

they really wanted to exclude that there was a tendon or muscle injury, uh,

2:00

like a traumatic tendon rupture.

2:01

And that's why we got MRI in this particular case.

2:04

So let's go back to our images here.

2:09

Uh, I like this really kind of more high resolution, fluid sensitive sequence.

2:14

It really demonstrates denervation edema and atrophy of this pronator Quadra

2:19

and of the FPL L.

2:20

And so this is really what was contributing to this patient's thumb weakness.

2:23

In this case, you can see the tendon itself is intact. And so, uh,

2:27

it was really thought to be some sort of nerve origin that was causing this

2:31

problem. Uh, as we really scrutinize this anterior nerve,

2:35

we don't see much. There's not a fibrous band, there's not an anomalous muscle.

2:40

There's really nothing along the course of the nerve that's causing impingement.

2:44

And so this ended up being what they thought was either a chronic kind of

2:48

repetitive pitcher or some sort of idiopathic injury. Um,

2:52

patient actually did okay with some hand therapy,

2:54

had some improved function of that thumb so he didn't have to undergo surgery.

2:58

We really see some fatty atrophy in association in this case. So, uh,

3:03

that was a good one. Very good job.