0:00

So the anterior interosseous branch, right,

0:02

or more distal branch

0:03

that innervates those deep flexor muscles.

0:06

Um, it can have direct trauma to it, uh, just

0:09

because of its course between the forearm bones.

0:12

So think about forearm fractures

0:13

that could potentially involve that nerve

0:15

and it can also have extrinsic compression.

0:17

Uh, so not really a chronic, repetitive injury

0:20

that's more the median nerve proper, uh,

0:22

but more likely extrinsic compression in these cases.

0:25

And these patients have a pretty,

0:27

a unique clinical presentation.

0:29

They actually have weakness of the thumb

0:31

and they have the inability to really form

0:33

what they call the circle sign

0:34

or when you give kind of an a okay.

0:36

Uh, they really can't interpose

0:38

that thumb in that index finger.

0:40

Um, and that's why this actually can mimic a flexor lysis

0:44

longest injury itself, right?

0:45

So a tendon injury, uh, can have a very similar presentation

0:49

to some of these denervation processes.

0:53

So here's a case example.

0:55

This was a patient who had chronic thumb weakness.

0:57

They also have that forearm pain.

0:59

Uh, and this was an instance

1:01

where they were questioning did they have some sort

1:03

of tendon abnormality or something else going on.

1:06

So we have a series of axial stir uh, sequences here,

1:09

as well as a more proximal T one weighted image.

1:12

And on our axial stir sequences, we see

1:14

that nice denervation muscle edema.

1:16

And again, it's in those deep flexor muscles.

1:19

So we see relative sparing of the more superficial flexors,

1:22

which suggests that this is just the anterior

1:24

interosseous nerve branch.

1:26

So when we follow the anatomic course of

1:28

that more proximal anterior interosseous nerve, uh,

1:32

we can see that it is abnormal

1:34

and it's actually being compressed by something

1:36

that's a little bit different.

1:37

And that's an accessory flexor, lysis longus muscle.

1:40

So this is not a normal, uh, region

1:42

of the flexor lysis muscle.

1:44

You can see how with, um, pronation

1:46

or with different provocative maneuvers in the forearm,

1:49

that you could get chronic compression

1:50

of this small nerve branch.