0:00

Moving to the radial nerve.

0:02

So again, still in that, um, kind of, um, lar aspect

0:05

of the forearm, but more on the lateral side.

0:08

Adjacent to the radius is where we have our,

0:10

um, radial nerve.

0:12

And our radial nerve similarly gives off a major motor

0:15

branch this time the posterior interosseous nerve.

0:17

So it also runs adjacent to the interrace membrane.

0:20

But now we're on the dorsal side of the forearm.

0:23

And as you might expect, uh, the radial nerve,

0:26

because it has a more dorsal course,

0:28

it innervates those extensor muscles

0:30

or most of the extensor compartment of the forearm.

0:33

And if we have more proximal involvement,

0:35

so if we have a radial nerve abnormality, we're expecting

0:39

to see some of those more proximal extensor muscles,

0:42

the brachial radialis, as well as the ECRL.

0:45

Um, if it's a more distal involvement

0:47

and we're into that posterior interosseous nerve branch,

0:50

then we expect to see some of these smaller distal extensor,

0:53

um, muscles that are involved in the ation process.

0:59

So I'm gonna talk specifically about posterior interosseous

1:02

nerve syndrome and pin.

1:03

And again, that's that small branch that can get entrapped

1:06

and that actually has a pretty long course.

1:09

And so there are multiple sites of entrapment of, uh,

1:12

the posterior interosseous nerve.

1:13

Some of these are named, so you you've heard

1:16

of things like the leash of Henry or the ARC froze.

1:19

Those are just different underlying causes

1:21

or different sites of entrapment of

1:23

that posterior interosseous nerve branch.

1:25

Um, you can have abnormalities of the joint that cause, uh,

1:28

issues here as well as the muscles

1:30

and the surrounding structures like the vessels.

1:34

Patients who have a posterior interosseous nerve abnormality

1:37

or an entrapment syndrome will present with the inability

1:40

to really extend their fingers.

1:41

So they have this finger droop where their fingers just kind

1:44

of naturally flex into a more relaxed position.

1:47

They're really unable to keep them extended.

1:50

It's a pure motor uh, phenomenon.

1:54

And so here's an example

1:55

of a posterior interosseous nerve entrapment.

1:58

Uh, and, and post

1:59

or those posterior interosseous nerve syndrome.

2:02

This was a 42-year-old woman.

2:04

She did have some paraesthesia,

2:05

but she had predominantly this weakness, uh,

2:08

in her wrist extension and her finger extension

2:11

and on her fluid sensitive sequences.

2:13

This is a proton density.

2:15

So again, we're not getting quite a star, a contrast

2:18

as we would see on our stir sequences,

2:20

but we can still appreciate that there's a,

2:22

a pretty big extent

2:23

of muscle signal abnormality in this instance.

2:26

And it's mostly in that extensor compartment.

2:28

So this makes us suspicious for some sort

2:30

of radial nerve abnormality.

2:32

Uh, when we go evaluate the radial nerve on the course

2:35

of the posterior interosseous nerve, remember that

2:38

that posterior interosseous nerve is deep

2:40

within the supinator muscle.

2:41

We identify it here and it's quite enlarged.

2:44

So those primary, uh, abnormalities, enlargement in the, uh,

2:47

overall caliber of the nerve, it's increased in signal.

2:51

Uh, we can barely even pick out some

2:52

of the other nerve branches in this particular, uh,

2:55

MRI sequence, but

2:57

that posterior interosseous nerve is really screaming hot.