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Today we are honored to welcome Dr. John Jacobson

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for a lecture entitled Ultrasound

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of Peripheral Nerve Entrapment.

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Dr. Jacobson is a board certified musculoskeletal

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radiologist and currently works at Lennox Hill Radiology in

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New York City and University of California San Diego.

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His academic achievements include over 260 peer reviewed

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publications and many invited national

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and international lectures and workshops.

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Dr. Jacobson has been a visiting professor on over 50

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occasions, is president of the Society of Skeletal Radiology

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and has received numerous teaching

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and mentoring awards,

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including the 2023 Distinguished Educator Award.

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He is also the author of the textbook Fundamentals

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of Musculoskeletal Ultrasound

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and we are honored to have him here with us today.

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At the end of the lecture, please join Dr. Jacobson in a q

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and a session where he will address questions you may have

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on today's topic.

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Please remember to use the q

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and a feature to submit your questions so we can get to

1:22

as many as we can before our time is up.

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With that, we are ready to begin today's lecture.

1:27

Dr. Jacobson, please take it from here.

1:30

Okay, great. So I'll be talking about ultrasound

1:34

of peripheral nerve entrapment.

1:35

As an aside, the QR code here will get you to a PDF

1:39

of my syllabus of this lecture.

1:41

I'll also have the QR code at the very end if

1:43

you can't get to your phone.

1:45

Uh, quick enough. Uh, these are my disclosures listed here.

1:49

They are really not relevant to the talk,

1:51

but they are listed nonetheless.

1:54

So first, a few introductory comments about

1:56

ultrasound of peripheral nerves.

1:59

They're best identified in short axis

2:01

because in short axis that's when they appear like this,

2:06

this honeycomb appearance

2:07

where you can see the individual hypo coic, nerve icic

2:11

and the echogenic neck tissue

2:13

around the, the nerve vesicles.

2:15

This is the median nerve in the carpal tunnel.

2:17

Obviously as you scan a nerve more peripherally,

2:21

as the sles will arbor rise

2:23

and move away from the trunk,

2:25

it will get smaller and smaller.

2:26

But when you look at a nerve trunk,

2:28

it's this honeycomb appearance that is characteristic.

2:31

Note here, I'm toggling the transducer

2:34

to help differentiate the adjacent tendons,

2:36

which are hyper coic demonstrating anisotropy.

2:40

Whereas the, the, uh,

2:41

nerve trunk themselves only the connective tissue will

2:45

demonstrate anoscopy.

2:46

So there's much less, uh, anoscopy.

2:50

You can see the nerves and long axis as well.

2:52

But the short axis is really how you identify the nerve

2:55

and how you can officially look at a nerve

2:57

throughout the entire extremity.

3:00

Another comment I wanna make is about nerve compression.

3:02

That's gonna be really

3:04

what I'm emphasizing in this lecture

3:06

on entrapment neuropathies.

3:08

What's been shown in the animal model is

3:10

that when you compress a nerve,

3:12

what happens is there's ischemia

3:15

and the first pathologic change is edema.

3:18

After that you have demyelination and then axonal damage.

3:21

The point here is that inflammation is not present

3:25

with nerve compression.

3:27

So the term neuritis is really a misnomer

3:29

and using that term is actually not very helpful

3:32

'cause it could, uh, trigger the clinician to think

3:36

that injecting steroids can cure the process when really

3:39

there is no inflammatory component at all

3:42

to compressive neuropathies.

3:45

What do we look for by imaging ultrasound and MR imaging?

3:49

What we're looking for is edema.

3:51

Again, that's the first stage of any kind of entrapment

3:54

edema of the nerve.

3:56

And also you'll see enlargement typically in many

3:58

of these locations

3:59

where I'll be talking about nerve entrapment

4:02

and the the swelling

4:03

or enlargement will be at, in proximal

4:05

to the entrapment site, a process

4:07

that's called axonal damming.

4:10

And then the, the edema

4:11

and the enlargement can persist more distally

4:14

that's most pronounced proximal to the

4:17

enclosed fibrosis canal or entrapment site.

4:23

Now when looking at peripheral nerves by ultrasound

4:26

or mr, we always have to be aware

4:28

of the end organ looking at the muscle

4:30

'cause this is a very helpful point

4:33

to determine the nerve distribution that is abnormal,

4:37

but also, uh, tells you the severity of of what's happening.

4:41

So I want to talk about this by ultrasound.

4:44

What we're looking at here is an example

4:46

of atrophy in the upper image.

4:49

So I wanna mention that edema appears hyper coic

4:53

and fatty uh, degeneration

4:55

or infiltration also appears hyper coic.

4:59

So I wanna take a moment about the physics of why both

5:02

of these different processes produce the same finding.

5:05

So if we talk about, let's talk about fatty degeneration

5:08

first, we know pure fat is nearly anti coic.

5:12

It's very hypo coic.

5:14

It's not really shown in this image,

5:16

but there's hypo area here in the subcutaneous area

5:19

that is pure fat.

5:21

You might wonder why is hypo coic muscle

5:24

in hypo coic fat when you mix this together?

5:26

Why does the muscle appear hypo coic?

5:30

Well it comes down to the physics of the image

5:32

because ultrasound,

5:33

we're essentially looking at reflections of interfaces.

5:37

What determines the reflectivity is the speed of sound

5:41

or impedance of the tissues across that interface.

5:45

So even though pure muscles hypoechoic

5:48

pure fat is hypo coic, their speed of sound is different.

5:51

So when they're interdigitated it produces reflections

5:55

because of those differences in speed of sound.

5:59

The same thing happens with edema.

6:01

We know fluid is anti coic by ultrasound,

6:04

but if you mix anti coic fluid with hypo coic muscle,

6:07

the speed of sound is different producing reflexivity.

6:11

Incidentally, muscle fibrosis also appears echogenic

6:14

and even muscle inflammation,

6:16

something I'm not talking about today will also

6:19

appear hyper coic.

6:21

The last point, if you're looking

6:23

for subtle increased genicity of muscle comparative

6:26

to compared to the other side, I've seen cases

6:29

where when you put the trans on the muscle,

6:32

the image looks really bright, you turn the gain down

6:35

so it starts to look like normal muscle.

6:38

What you really wanna do is look at the contralateral

6:40

asymptomatic side,

6:42

set the gain appropriately based on the background light

6:45

of the room and then go to the symptomatic side.

6:49

Alright, so what I'm gonna do in this lecture is run

6:52

through the peripheral nerves, starting

6:54

with the upper extremity,

6:56

covering the entrapment syndromes first, beginning

6:58

with carpal tunnel syndrome.

7:01

Of course the most common entrapment neuropathy

7:03

of the upper extremity.

7:05

Now there are a bunch of numbers

7:06

that are listed which are here on the slide to

7:09

indicate if you needed to, uh, look at the size

7:13

of the area to be more exact.

7:16

With the diagnosis you can do so.

7:18

In fact, when I think about ultrasound

7:20

of peripheral nerve entrapment of of the extremities,

7:23

this is probably the only nerve

7:25

where I will actually measure the area

7:28

because of litigation issues

7:31

and also many insurance companies need more strict criteria

7:36

met to, to approve various treatments

7:38

for carpal tunnel syndrome.

7:40

Anyways, these these are the numbers uh, you may apply.

7:44

Now here's what it would look like.

7:46

The peripheral never will be enlarged and hypo coic.

7:49

Here we see in cross-section the nerve indeed is enlarged

7:53

and the echogenic connected two layers are really

7:57

more hypo coic.

7:58

Globally, the entire median nerve is hypo

8:02

coic in long axis.

8:04

On the right we can use the bone landmark for orientation.

8:08

Here's radius lunate and capitate.

8:12

We can see the enlarged hypo coic nerve going

8:15

underneath the defensive carpal ligament or ret inoculum.

8:18

Some people have coined the term the notch sign.

8:21

It's basically showing a difference in thickness

8:24

related to compression.

8:26

Note the adjacent here, which are more hyper coic

8:31

and fibrillar or fiber like.

8:34

Now if you are to measure the area of a nerve,

8:38

it's done on short axis.

8:40

You wanna toggle the trans define the epineurium,

8:43

which is the white layer surrounding it.

8:46

You wanna find the area of maximum enlargement

8:49

and using circumferential trace, don't try to put an ellipse

8:53

to it or X times y that is inaccurate.

8:55

You wanna trace on the inside of the epineurium

8:58

for the most accurate assessment

9:01

or measurement of the area of the nerve.

9:05

Now one problem about using just a single number to indicate

9:10

what is abnormal, meaning a number

9:11

that you can apply to everyone.

9:13

The problem is someone who's five foot versus six foot

9:17

eight, their nerves are intrinsically different size.

9:20

So this is the, the criterion I use

9:23

to diagnose carpal tunnel syndrome when I'm measuring

9:25

nerve enlargement.

9:27

And you can see the numbers here are really quite good.

9:31

What the paper described as you measured the nerve area

9:35

at its maximal enlargement

9:38

and you compare to the thighs more proximal at the level the

9:41

pronator quadrats.

9:43

If that area increases by two millimeter square

9:46

or more, that's when you get 99% sensitivity.

9:50

100% specificity in the diagnosis of carpal tunnel syndrome.

9:58

Here is another case

10:00

of carpal tunnel syndrome showing nerve enlargement.

10:03

Now most of the time when we see carpal tunnel syndrome,

10:07

there's really no uh, I guess physical finding,

10:10

meaning there's no ganglion cyst

10:12

or there's no uh, synovitis usually in most cases.

10:15

So here's an unusual case, a patient

10:17

with rheumatoid arthritis.

10:19

What we see here is synovitis

10:21

around the flexor tendons associated

10:23

with the carpal tunnel syndrome.

10:26

Now the OAR, technically this is not no synovitis,

10:29

there's no tendon teeth.

10:30

Here is actually ulnar bursa

10:32

that essentially functions like tendon teeth.

10:35

You can still call it you incentivize,

10:37

although it's not completely accurate.

10:39

It's really the ulnar bursa interdigitating

10:41

between the flexor tendons within the carpal tunnel.

10:46

As we leave carpal tunnel syndrome.

10:49

Remember you can have a bifid median nerve is a normal

10:52

variant some people say up to 10% of the time,

10:55

and indeed those can be enlarged

10:57

and hypo coic with carpal tunnel syndrome.

11:00

The criterion used here is four millimeter square.

11:02

If you add the numbers together compared

11:05

to proximal measurement,

11:07

and as an aside, you should not see flow on color

11:10

or power doppler imaging in a normal nerve.

11:12

So that can be another indirect sign

11:15

of carpal tunnel syndrome.

11:18

Moving on to another entrapment syndrome

11:20

of the median nerve pronator tear syndrome.

11:23

What this involves is the median nerve as it passes

11:26

between the two heads of the pronator terrace.

11:29

This is really quite rare.

11:31

This is the only case I've seen

11:33

and uh, what we're looking at here is indeed

11:36

nerve enlargement.

11:37

Now why I think we do not see this well at imaging is

11:42

that unlike the carpal tunnel

11:43

where you have an enclosed fibrosis canal creating this

11:48

axonal damning and edema that's constant.

11:51

This is more of a physiologic entrapment

11:53

where the nerve is compressed but not continually.

11:56

And that's why we don't get this dramatic enlargement

11:59

and edema of the nerve proximal to the entrapment site.

12:03

But this is again, quite rare.

12:07

Moving on to anterior interosseous nerve syndrome,

12:10

there is problems when trying to make this diagnosis

12:14

and then the reason they're twofold, first of all, looking

12:17

for the anti interosseous nerve is challenging

12:19

even in normal people.

12:21

If you put on the color of dopplar imaging,

12:23

it's usually sitting right next to the the art artery here.

12:26

But why this makes this very difficult is the end organ,

12:32

which are the muscles which shrink denervation.

12:35

What that will do, it really obscures the deeper structures.

12:40

It dampens the, the strength of the ultrasound beam.

12:43

So what I find in trying

12:45

to diagnose anterior neurosis nerve syndrome,

12:48

I'm really relying on looking for the end organ

12:50

or the denervation changes also shown here

12:54

on on the MRI.

12:57

Now there is a clinical exam finding that can help you

13:00

to indicate yes, this really is a problem

13:03

if you have them make the okay sign.

13:04

If they cannot make the okay sign, they are not okay.

13:08

So that is the clue to the diagnosis.

13:13

Moving on to the ulnar nerve hurts at the wrist

13:17

in gull's canal

13:18

or the ulnar conal is where we're looking

13:21

for the ulnar nerve being compressed.

13:24

Now you can have an accessory abductor de gene up

13:27

to 24% of the, of wrist.

13:29

I think it's more about 20%,

13:31

but this is what the literature says

13:33

that can cause compression uncommonly,

13:36

you could have what's called hypo

13:37

or hemorrage syndrome where the primary problem is nar nerve

13:41

thrombosis, but you could have edema swelling with

13:44

mild secondary nerve compression.

13:47

So here's an example of an accessory abductor DigiMe.

13:51

What we're looking at here is the pisiform

13:54

is my bone landmark.

13:55

We know in the transfer plane between the ulnar artery

13:58

and the pisiform is the ulnar nerve.

14:01

The ulnar veins are collapsed.

14:03

You should not see any muscle in this area.

14:05

And this is the accessory muscle most commonly going over

14:09

the top of these structures uncommonly introduced

14:12

between the ulnar artery and nerve.

14:15

But you can see here the hypo calic muscle,

14:18

the linear fiber adipose layers

14:20

between the muscle characteristics of normal muscle tissue.

14:25

I've seen ganglion this year uncommonly lipomas.

14:28

It, it's not, it's not very common,

14:30

but you can have masses in the area

14:32

also causing compression.

14:34

Now here's an example of hypo

14:36

or hammer syndrome historically described in Europe

14:39

where people are using their hand to shingle roofs.

14:43

I don't recommend that this is more people falling on their

14:46

hand or people using racket sports.

14:49

And what we see here is thrombosis in the ulnar artery

14:53

and thrombo more.

14:55

The point here is the edema

14:57

and swelling related to the ulnar thrombosis.

14:59

You could have some ulnar nerve symptoms,

15:02

but not truly an entrapment neuropathy per se.

15:06

And here's the companion case.

15:08

This entrapment neuropathy is really between the hook

15:11

of the hammit and the handlebars of a bicycle.

15:14

So this has been called cyclist risk, where having the hand

15:18

or wrist resting on the the,

15:20

the bicycle handlebar will compress the nerve

15:23

between the handlebar

15:24

and the hook of the hammit producing the

15:26

ulnar nerve symptoms.

15:31

Now moving on to the cubital tunnel syndrome,

15:33

the second most common infra neuropathy

15:36

with neuro upper upper extremity.

15:37

Let's look at the anatomy. The true cubital tunnel is this

15:42

canal here where the alt, where the ulnar nerve passes

15:45

underneath the arcuate ligament

15:47

and point between the two heads of the flexor CRI mars.

15:51

Now remember what we're looking for here is edema

15:54

and enlargement at in proximal ENT treatment site.

15:58

So we tend to see this edema more proximal

16:01

behind the mi peon.

16:03

So that's where I'll start imaging, look for the enlargement

16:06

and then look for the uh, transition

16:09

or compression of the nerve

16:11

as we look distally within the true cubital tunnel.

16:15

Here's an example where the nerve is markedly enlarged.

16:19

You look here in, in long axis the nerve getting larger

16:21

and larger emus and then compressed under the RQA ligament.

16:26

Now there are a number here,

16:27

but I have to admit I usually don't need

16:30

or need to measure the, the, the area here.

16:34

And the point here is when you're scanning a peripheral

16:36

nerve, you need to scan the entire nerve.

16:39

However, recognizing there are specific sites in the

16:42

extremity prone to entrapment

16:45

and as you're scanning the nerve in short axis, again that's

16:48

how you identify the nerve.

16:49

The nerves should not enlarge,

16:51

they should arize and get smaller.

16:53

So as you're scanning the nerve in short axis,

16:56

as you approach a fibrosis canal like the cubital tunnel,

16:59

the nerve will start to enlarge and get more hypo coic.

17:03

And then as you enter into the entrapment site,

17:06

the nerve will get smaller.

17:08

So just moving the transistor back

17:10

and forth, even without measuring,

17:12

usually I can subjectively know that there's going

17:15

to be some entrapment neuropathy.

17:18

The second thing is where the nerve is emus enlarged,

17:21

it is very sensitive to ultrasound pressure.

17:24

So by pushing with the transducer it will elicit symptoms

17:28

so you can get that feedback as well.

17:30

So usually I'm making up my diagnosis in short axis alone

17:33

without any measurements.

17:35

Of course, you can look in long axis to complement,

17:38

which I'm showing here

17:39

and you can measure if you choose to do

17:42

so like I do in the carpal funnel.

17:47

Here's an example, I'm ancon.

17:50

When you look at the culet tunnel region here,

17:53

the MRI is turned upside down with the elbow extended.

17:57

You shouldn't see any muscle overlying the area

18:00

of the ulnar nerve.

18:02

And here this is the abnormal situation.

18:05

Remember not to call this a cyst or a mass.

18:08

Recognize the hypo coic muscle and the fibroadipose layers.

18:12

Here is the ulnar nerve.

18:14

But two points I wanna make about this.

18:16

First of all, it is very common to see edema

18:20

of the ulnar nerve without enlargement

18:22

in a normal situation.

18:24

Asymptomatic patients,

18:26

and we see this on MRI as well, it's been shown that

18:28

of all the nerves in the extremities,

18:30

minimal edema on the ulnar nerve without enlargement is a

18:34

combin asymptomatic finding.

18:36

And this can be explained,

18:37

if you think about the nerves in the extremities,

18:40

the ulnar nerve is one nerve

18:41

that really goes through a lot of flexion.

18:44

As you bend the elbows, you're, you know, you're,

18:46

you're going a hundred eighty, two hundred seventy degrees.

18:49

This nerve is making it a tremendous term

18:52

and this is why in theory you can have asymptomatic edema

18:57

of the ulnar nerve but it should not be enlarged.

19:01

The second point I wanna make, you want to scan this area

19:05

with the elbow in extension.

19:08

And that is because when you flex the elbow,

19:10

the biceps comes into view

19:12

and our accuracy in diagnosing this accessory

19:15

muscle goes way down.

19:17

So you want to start with the elbow extended

19:19

or nearly fully extended

19:21

and then make sure that there's no muscle in this area

19:25

indicate this normal variant.

19:28

Now speaking of elbow flexion, when someone has

19:32

NAR nerve symptoms, we're also going to look dynamically

19:35

and look for NAR nerve dislocation.

19:38

Now this can happen in up to 20%

19:40

of asymptomatic individuals, but

19:43

nonetheless we're going to look for this.

19:45

You put the transducer on the media epicon down

19:48

as you flex the elbow norm phy stay behind the epicon down.

19:53

Here's the abnormal situation here.

19:55

It's coming with a top snapping back.

19:59

Don't put too much pressure with the transducer

20:01

'cause you can inhibit the nerve from going back and forth.

20:05

So obviously the nerve snapping in

20:07

and out, that can cause some edema of the nerve

20:10

and irritation also having the nerve out

20:13

of its normal protected area predisposes it

20:15

to direct impact injuries.

20:19

Now when we're looking at the ulnar nerve for dislocation,

20:23

we have to be aware of what's called snapping tricep

20:25

syndrome in this scenario indeed the ulnar nerve dislocates,

20:30

but there's an additional finding.

20:32

The medial head of the triceps shows subluxation.

20:36

And I'll show you what this looks like

20:39

and your yours on the left.

20:40

I'm gonna start the thin clip.

20:42

Here's the medi condyle

20:44

and a neutral position here is the only nerve.

20:47

Now I'm gonna flex and look what happens.

20:50

Dislocated nerve snapping of the triceps

20:53

and as we extend the elbow we can see both

20:57

of these coming back to their normal location.

21:00

Why this is important to consider is clinically this may be

21:03

difficult to to pick up

21:06

so many times the only nerve dislocation is easily felt

21:09

clinically, but this can be problematic.

21:12

There's one case that comes to mind of a violinist who, uh,

21:16

went to surgery for all nerve dislocation,

21:18

didn't have imaging after the nerve, uh,

21:21

trans transposition, uh, the patient still had symptoms.

21:25

Patient came back for our imaging

21:27

and the patient had snapping triceps

21:29

that was not in anticipated, had to go back

21:32

for a second surgery to debride the muscle.

21:35

So it's important to consider this where both

21:37

of these structures are abnormally moving over the menon.

21:42

Okay, moving to the radial nerve

21:44

and posterior interosseous nerve syndrome.

21:49

When we follow the radial nerve between the brachialis

21:53

and brachial radis,

21:55

it will divide into a superficial and deep branch.

21:58

When the deep branch goes between the two layers

22:01

of the supinator under an edge of connective kit, uh,

22:04

tissue called the Arcadia fros, that is

22:07

where the entrapment occurs.

22:08

The nerve looking for edema

22:10

and enlargement at end proximal to the entrapment site,

22:14

the deep branch will go into the supinator

22:16

and exit as the posterior

22:19

ous nerve in the dorsal part of the forum.

22:23

So it's interesting, many people will divide this into two

22:27

subtypes of syndrome, supinator syndrome,

22:30

and radial tunnel syndrome for Supinator syndrome.

22:34

That's when there are motor deficits.

22:36

Abnormal electrodiagnostic studies

22:38

and imaging will show nerve enlargement and edema.

22:41

Ultrasound and mr this is what we typically see

22:45

where we see the normal nerve on this contralateral side

22:48

here we see enlargement

22:50

and edema as it goes at the edge of the AAD fro

22:53

between the two layers of the supinator.

22:57

Now radial tunnel syndrome is more problematic.

23:00

Patients have pain but there are no motor deficits,

23:02

normal electrodiagnostic studies and no nerve enlargement.

23:06

However, we do see muscle denervation on mr.

23:10

So that's why if I'm scanning for, uh,

23:13

PostIt interosseous nerve syndrome on ultrasound,

23:15

if it's normal, I'll have them go to MR.

23:18

Knowing that it is more sensitive on MR

23:20

to see this subtle muscle edema

23:23

that could indicate radial tunnel syndrome.

23:27

Moving on to Wartenberg syndrome,

23:29

looking at the superficial sensory branch

23:31

of the radial nerve toward the forearm and wrist.

23:35

Now we can easily find the superficial branch

23:38

of the radial nerve as it courses over

23:40

the first risk compartment.

23:41

Of course, this is where we look for tenitis.

23:45

Here's the honeycomb

23:46

or speckled appearance

23:47

of the superficial branch for the radial nerve.

23:51

We, this is not the site of wardenberg syndrome,

23:53

but I just wanted to highlight

23:54

where you can identify the nerve easily.

23:57

Where I tend to see problems here is a hematoma

24:00

and compression due to any puncture injury, et cetera.

24:04

So this is more

24:05

of a traumatic problem more than wardenberg syndrome.

24:10

But looking at wardenberg syndrome, this is more,

24:12

more proximal to the forum, still the distal part.

24:16

And what we're looking at is where the nerve comes out, uh,

24:20

over the uh,

24:21

brachial radiology under the EC carpe radiologist.

24:25

And when the hand is pronated, that's

24:28

where the compression occurs.

24:29

And here we can see the hallmark of an entrapment neuropathy

24:33

or compression, which is edema

24:35

and enlargement at the compression site.

24:38

So sometimes finding the nerve at

24:40

this location is challenging.

24:41

That's why I started by saying

24:43

where you could find the nerve more proximally,

24:45

then you can move, sorry, more distally

24:48

and then move proximal.

24:49

You can always look at the elbow and

24:51

and then track it distally that way as well.

24:53

But this is the finding that we see

24:55

with Wharton Bird syndrome.

24:58

Interesting. The upper extremity looking at the

25:01

suprascapular nerve really related

25:03

to a paralabral gang leaf cyst,

25:05

we use the term paralabral cyst to indicate

25:08

that this is caused by a labral tear

25:11

where joint fluid will come out of a joint,

25:13

usually labral detachment producing, uh, the cyst.

25:18

They can occur in the spinal glenoid notch

25:20

where you would have downstream atrophy

25:22

of the in infraspinatus

25:24

or you can have it at the suprascapular notch affecting more

25:28

approximately therefore the supraspinatus.

25:30

And in infraspinatus.

25:32

And here's the labrum, here's the glenoid,

25:35

here's the humeral head.

25:38

We're not that great in looking for labral tears

25:40

with ultrasound, but

25:41

nonetheless, if you see a multilocular cyst at the base

25:45

of the labrum, look carefully for the labral care

25:48

and usually you can adjust it at least here.

25:51

Incidentally, the infraspinatus muscle is

25:55

emus showing increased genic on ultrasound.

25:58

Therefore denervation changes as you know,

26:01

the earliest signs of denervation is edema.

26:04

And then later on is

26:05

where you'll see fatty infiltration or degeneration.

26:08

And finally atrophy

26:10

where there's decreased size of the muscle.

26:12

Now when performing ultrasound for a paralabral cyst,

26:16

we have to be aware of normal suprascapular vein

26:19

dilatation or dilation.

26:22

Here's the normal shoulder looking at the infra muscle

26:25

and tendon humeral head labrum and the posterior glenoid.

26:29

Here's where we're gonna look for the scapular nerve.

26:33

Now look what happens. As we accidentally rotate,

26:36

we see normal suprascapular vein dilation.

26:41

So if this, if I froze this image right here,

26:45

this looks almost exactly like a pair of labral cys.

26:50

Now how you can differentiate this from a tru cyst, uh,

26:55

don't rely on color doppler tracing.

26:58

The flow is so slow with this dilation

27:00

that even the waveforms are negative.

27:03

But the key is what I'm showing here,

27:05

this is a transient finding,

27:07

meaning when you internally rotate, it collapses.

27:11

When you x-ray rotate it dilates, you will not see

27:14

that happening with a paralabral cyst.

27:17

Those are somewhat tense, they're under pressure.

27:21

The fluid is is quite uh, viscous.

27:24

It's not going to fully collapse like this.

27:26

That's how you make this extinction.

27:30

Okay, moving on to the lower extremity.

27:32

First, speaking with the perineal nerves.

27:35

I recognize the newer graduates from medical school are

27:39

using the term fibular nerve.

27:41

Um, but nonetheless I'm still using the term perineal,

27:44

starting with the common perineal nerve.

27:47

As you know, this tracks behind the the biceps fems,

27:50

which is cut here to show the nerve.

27:52

One potential infra site is when it goes

27:56

between the fibula and the perineal long muscle.

28:00

Of course we know that a fracture

28:01

of the fibula can produce injury.

28:04

I'm gonna show a companion case of stretching injury

28:06

with a nerve dis a knee dislocation.

28:09

But for entrapment neuropathy, focus on first.

28:15

Here's an example here is the fibula.

28:18

And as I start the cine clip you can see the nerve getting

28:21

enlarged as it goes underneath the proximal as back

28:25

of the peroneal long.

28:27

This was a golfer who developed foot drop.

28:30

There was no trauma, it just he with his activity,

28:34

this became enlarged

28:36

and it set up this entrapment neuropathy and his foot drop.

28:42

Now here's a companion case, not an entrapment neuropathy

28:44

but nonetheless I wanna show it for completeness sake.

28:47

This is a patient who had a knee dislocation.

28:50

We can see edema here of the commissural nerve

28:54

compared to the nerve.

28:55

So of course we can't forget to look for that.

28:58

And here it's the tibial nerve, it's a speckled appearance

29:01

and the EMS appearance of the uh, common perennial nerve.

29:06

And as I start the thinning clip, you'll see

29:08

how enlarged this nerve gets compared to the tibial nerve.

29:14

Sorry, the arrows are, are not moving as they did.

29:17

But nonetheless you get the idea that

29:22

this is hypo coic thick compared

29:24

to the normal particular appearance.

29:26

Here it is in long axis.

29:28

Again, nerves should stay the same size

29:30

or our horizon get smaller.

29:31

They shouldn't get larger and definitely not hypoechoic.

29:36

Now somewhat of an entrapment neuropathy, what's more

29:39

of a compressive neuropathy has to do

29:41

with the perineal intraoral ganglion cyst.

29:44

This is a really interesting phenomenon really

29:48

describing other nerves.

29:49

This by far is the most common nerve that we see.

29:51

This what will happen is a patient may have a palpable mass

29:56

at the fibular neck or head region.

30:00

Now typically when a patient develops foot drop,

30:03

many times it's assumed clinically

30:05

that it is just incidental.

30:07

And it we see this with patients who cross their legs maybe

30:12

with trauma or with with weight loss

30:14

because they're more likely

30:16

to compress the nerve externally.

30:18

But one must realize that almost up to 20% of those patients

30:22

with foot drop, this is due to an intradural ganglion cyst.

30:26

Now what is interesting, unlike the idiopathic variety

30:29

with people with weight loss, we see this with patients

30:33

with a high body mass index.

30:35

And let me explain why this relates

30:38

to the intraoral ganglia cyst.

30:42

So first of all, uh, we know

30:45

that the fib fibular joint connects

30:47

to the knee joint in about 20% of the population.

30:50

And what has been shown that if you have a high BMI,

30:54

you're more likely to have uh,

30:56

osteoarthritis or a cartilage problem.

30:58

Therefore you're more likely to have a joint effusion.

31:02

And with a high BMI, you're more likely to have

31:04

that joint effusion under pressure.

31:07

And if you're one of those 20% where

31:09

that need joint connected to the proximal uh, ular joint,

31:14

then joint will be pushed into this joint.

31:17

And if that happens chronically,

31:19

what will happen in some people is

31:22

that fluid will be pushed into the articular branch of

31:26

of the branch

31:27

and then this fluid can track into the common peral nerve.

31:32

Basically that's the pathophysiology

31:35

of a perineal intraoral ganglion cyst.

31:38

It's been shown that if you inject contrast into the knee

31:40

joint, not necessarily the tibial filar joint knee joint,

31:44

it can actually connect into this ganglion cyst.

31:48

And like all ganglion cyst all over the body,

31:51

it's a multilocular hypo coic anti coic collection

31:55

of fluid connecting to a joint.

31:57

Somehow this one is connecting via a nerve.

32:01

We talked about the paralabral cyst where

32:04

that ganglion type cyst connects to the shoulder joint

32:07

al joint through label detachment or tear.

32:10

So back to this by MRI, this can be challenging.

32:15

It's been called a signet ring sign

32:17

where you see a small ganglion fist next

32:20

to the common perineal nerve.

32:22

Here it is tracking along the articular branch.

32:25

Now why this is challenging on MRI, first of all,

32:28

if the history says pain, this almost looks like one

32:31

of these veins in the subcutaneous fat,

32:33

hopefully the the history will guide you to the problem

32:37

'cause it can be subtle when they're small.

32:39

Here on the ultrasound the typical appearance

32:42

of a ganglion cyst, multilocular, hypo

32:45

or antico, we see a tracking along the fibular neck

32:49

and tracking along the common perineal nerve.

32:53

Now here's a companion case.

32:55

This is an extended field of view.

32:57

These are one centimeter markers here,

32:59

this thing was over 15 centimeters going

33:01

into the satic nerve.

33:05

So what we see here is the multi fluid collection

33:10

and I'm showing here now the effect of that,

33:13

the fatty infiltration and edema of the common

33:16

or the extensor muscles of the leg.

33:18

And here we see denervation edema on the MRI.

33:23

So these can be quite enlarged.

33:27

Continuing now to the superficial peroneal nerve.

33:31

Now this site is prone for entrapment where it pierces the

33:36

curl fascia of the leg,

33:37

approximately nine centimeters up from the fibula.

33:40

And that is the typical site

33:43

and what we'll look for, just like any intra neuropathy,

33:45

edema and enlargement.

33:49

But here's a case where I was scanning this young lady's

33:52

ankle and the history was pain.

33:55

I went through my entire ankle

33:57

protocol looking at the tendons and ligaments

33:59

and joint et cetera.

34:00

And everything was completely normal.

34:03

And what I typically do, especially in the ankle,

34:05

in the foot and the wrist, in the hand when I'm scanning

34:08

someone with ultrasound, I'll ask them to point where

34:11

with one finger where the problem is

34:13

or explain what's going on.

34:15

And what she said was that I have pain

34:18

and numbness shooting down my leg.

34:20

So of course when you hear that history,

34:22

you think this is a nerve problem.

34:24

And I said, please explain more.

34:26

And she said, whenever I am exercising

34:29

or she was actually a ballet dancer, uh,

34:33

this would create the problem.

34:35

So I asked her to reproduce the symptoms

34:38

and what I saw here was the superficial

34:43

branch of the perineal nerve going enlargement

34:46

as it comes out under the fascia.

34:49

And at the site there was a muscle hernia.

34:52

So this was a muscle hernia creating this,

34:55

this entrapment at the entrapment site.

34:59

So the resolution of ultrasound showed the nerve problem

35:03

and the interaction with the patient of course,

35:06

and the dynamic imaging brought out the muscle hernia,

35:09

which was really contributing

35:11

or I would say causing the nerve entrapment

35:14

at its entrapment site.

35:17

And we know muscle hernias occur in the lower extremity,

35:19

most commonly the tibia s anterior

35:21

where you have penetrating vessel vessels,

35:23

which is weakening the fascia.

35:25

Alright, moving on to the tibial nerve.

35:30

The tibial nerve. Remember it's not the posterial nerve that

35:33

that's, that's an incorrect term.

35:35

There's only one tial nerve and here it comes down here

35:39

and it has different ways it can bifurcate an arbor rise.

35:44

It gives off a medial calcaneal branch,

35:46

which is sensory in the subcutaneous fat of the heel.

35:50

Then you have the two larger branches, the medial

35:52

and lateral plantar nerves.

35:55

Sometimes all three come off at the same time

35:57

as a trifurcation.

35:59

And then you have the inferior calcaneal nerve

36:02

and you call it Baxter nerve, which is the first branch off

36:05

of the lateral plantar nerve.

36:07

This one is really difficult to identify an ultrasound.

36:11

These two are easy. This one you can typically see now

36:16

because this is an enclosed base, this is

36:19

where we're prone to entrapment.

36:21

By far the most common cause of entrapment is a gangly cyst.

36:25

You can have other causes, masses, et cetera,

36:28

but it's really, that is the problem.

36:30

Now side point I wanna make, if you

36:35

consider all the entrapment neuropathies

36:36

that I've talked about so far in both extremities,

36:40

the one entrapment

36:41

that creates the most dramatic nerve enlargement is

36:44

cubital tunnel syndrome.

36:46

On the other end of the spectrum, the one where I've,

36:48

I've not yet to date seen enlargement

36:51

of the tibial nerve is the tarsal tunnel.

36:54

And this can be explained

36:56

by the pathophysiology of the edema.

36:59

Remember the edema is due to what's called axonal damming.

37:02

So it turns out the enlargement edema is proportional

37:06

or indirectly, sorry, inversely proportional to the size

37:10

of the entrapment space.

37:13

So the cubital tunnel is a very narrow space.

37:15

That's why the ulnar nerve is dramatically enlarged.

37:18

The tarsal tunnel is one of the largest spaces

37:21

that the nerves pass through.

37:23

So that's why we do not see enlargement.

37:26

And I've actually not seen a emon MRI as well in spite

37:29

of a clinical finding

37:31

and even a ganglion cyst pushing on the nerve.

37:33

There's just so much space there that it's

37:36

that we don't see the dramatic features of edema

37:39

and enlargement like the other nerves.

37:42

Uh, carpal tunnel syndrome's another one not as striking

37:45

as culet tunnel,

37:47

but definitely in this area in tar tarsal tunnel.

37:51

Don't expect the nerve to look abnormal.

37:53

You really wanna look for the cause of the entrapment.

37:57

Another point when you're scanning, don't scan in this area

38:00

because you can have problems more distally.

38:02

I'm gonna show a case of a ganglion cyst from the anterior

38:05

sub joint that was presenting as tarsal tunnel syndrome.

38:09

And the problem was actually beyond the tarsal tunnel.

38:12

So first of all, normal here's showing the

38:15

trifurcation of the tibial nerve.

38:17

We're showing the medial calcaneal branch

38:20

and then the lateral and medial plantar nerve,

38:23

which is the um, arborization of the tibial nerve

38:29

here taken from the literature showing the inferior

38:32

calcaneal nerve here between the abductor and the quadros.

38:37

Plenty. Now even with mr,

38:39

I still have not seen an abnormality of this nerve.

38:43

What I do rely on with ultrasound

38:45

and MRI is the end organ of this nerve.

38:49

What we're looking for here is basically edema

38:53

and fatty atrophy of the abject digital quinty.

38:58

Now remember there are different levels of entrapment

39:01

of the inferior calcaneal nerve.

39:04

Actually the more common one is going to be a, uh,

39:07

plantar aosis

39:08

and ified spur where the nerve tracts under that.

39:12

We can't see that with ultrasound anyways.

39:15

So just be aware that this nerve is hard to see

39:17

and that's why when I'm looking at the TORS tunnel region

39:20

and any for medially for nerve symptom,

39:23

look at the abductor dig quinty for fatty infiltration

39:27

or edema as a to some kind of entrapment, more proximally.

39:33

I already mentioned this ganglion cyst is

39:36

by far the most common rarely these other items

39:40

and I just talked about the length

39:42

real nerve is usually relatively normal.

39:46

Here is a larger talked to ganglion cyst,

39:49

again cyst all over the body.

39:51

He had the same pathophysiology and they look the same.

39:54

The pathophysiology is joint fluid, most commonly coming

39:58

through a defect in the capsule of the joint.

40:02

And you have fluid pushing it out into the soft tissues,

40:05

forming a multilocular hypo IC collection.

40:09

Here with through transmission the flu can be very viscous

40:13

like these little doc shown here.

40:15

And here the tibial nerve is being displaced

40:18

or the tibial nerve is otherwise normal in size

40:22

and echogenicity.

40:26

Now here is that companion case

40:28

where the caral toleration was completely normal,

40:31

but as I scanned more distally, I saw

40:34

that the medial plantar nerve was displaced

40:37

by the soft tissue ganglion.

40:38

This coming from the anterior subtalar joint here,

40:43

the middle face set of the anterior uh, anterior uh, joint

40:48

and the nerve was irritated.

40:49

You pushed on the transducer

40:51

and the patient, yes, you're eliciting the symptoms.

40:53

So you get that feedback telling, uh, telling us

40:56

that we're in the correct area.

40:59

Now here's a rare example of soft tissue varice

41:03

creating tarson syndrome.

41:05

Now I don't know

41:06

how many vessels should be considered abnormal.

41:09

I haven't seen that literature either.

41:11

I basically compared to the other side

41:14

and this was like I saw 10 different

41:16

vessels compared to two.

41:18

So I know it was asymmetric

41:20

and the patient had tarsal tunnel syndrome.

41:23

So this was a suggestion of the cause.

41:25

There was no other cause for it. So we presume that.

41:28

So I'm just saying this is a subjective finding I would

41:31

compare to the other side.

41:35

Okay, finally, in the next four

41:37

and a half minutes, I'm going

41:39

to cover a common plantar nerve.

41:42

So first the anatomy. Now this is very important as we sort

41:46

through how to image interal aromas.

41:49

The key here is this transverse manar ligament connecting

41:52

the plantar bursa.

41:55

The inner metatarsal bura is dorsal to

41:58

that in the metatarsal heads

42:00

where the neurovascular structure are plantar,

42:03

they're in different locations.

42:04

These two things because of this inner metatarsal,

42:09

or sorry, transverse metatarsal um, ligament.

42:13

So that's why I scan plantar.

42:15

So interdigital nerves, uh, neuromas,

42:18

this is really an entrapment.

42:19

The common plantar digital nerve branches, edema,

42:22

fibrosis and necrosis.

42:24

Third, more than second inter spaces females

42:27

and wearing high heels.

42:29

Um, someone with more pliable foot, whatever that means

42:33

to narrow toe box shoes will do it.

42:35

They can matic up to a third

42:37

and especially if they're under five millimeter measuring

42:41

medial to later.

42:43

Now what's interesting, people use the term marching aroma

42:47

freely and actually many times incorrectly.

42:50

I know because I had done that for a long time.

42:53

I now am corrected where the only neuroma

42:56

that is a Morton neuroma is the third inner space.

42:59

The other ones have other names.

43:02

So what I've learned through the years is I never wanna use

43:04

an epi member again,

43:06

that way I know I won't use it incorrectly.

43:08

Uh, you can use them, but I think it's kind of,

43:11

oh whatever I I just call 'em interventional aromas

43:14

and indicate the web space.

43:18

Okay, so scanning from a plantar aspect, I again want

43:22

to highlight the location

43:24

of a bursa versus an aroma in white.

43:28

Here we have the transverse metatarsal ligament.

43:31

We know that the inter metatarsal bura is dorsal

43:34

between the metatarsal heads.

43:37

The pathophysiology is that the plantar digital nerve.

43:40

When it course over the edge of this

43:43

transverse metatarsal ligament, that's

43:46

where the neuroma forms, therefore the neuroma will be more

43:49

distal and more plantar at the edge of this ligament.

43:55

So here on MRI

43:56

and ultrasound, we can see the neuroma

44:00

a dumbbell appearance.

44:01

It's plantar. Remember, more torso is going to be the bursa.

44:05

There are different locations here.

44:08

It's hard to tell the difference.

44:09

I'll explain how we can, but this is the neuroma

44:12

and this is the bursa.

44:14

And what's interesting that's not interesting.

44:17

When I'm in, when I, when I'm interpreting Mr,

44:21

I really rely on this now I really rely on this long axis

44:25

view of the metatarsals.

44:28

Knowing that the pathophysiology in aroma goes

44:32

beyond the transverse metatarsal ligament.

44:35

A bursa usually will not extend that far.

44:39

So unless it's dramatically enlarged this,

44:42

not only this pedunculated appearance going,

44:45

I really rely on it going distal as well.

44:49

Alright, let's get to the ultrasound.

44:53

Now when I'm scanning it from a plantar approach,

44:56

here is the edema of the nerve coming over the top

45:00

of the transverse metatarsal ligament.

45:03

Note that the bursa is more koic

45:05

and it's oral to the ligament nerve

45:08

as it comes over the edge of the ligament forms the neuroma.

45:11

So the neuroma is more distal and more plantar.

45:16

They look different. Also when you perform the ultrasound,

45:19

the verse is often compressible

45:21

and this is minimally if all compressible.

45:26

Alright, three steps. How I perform this ultrasound.

45:29

I always have my finger on the other side playing the

45:33

apart and applying pressure.

45:37

And the normal interdigital space will be low level echoes

45:40

like this fibro fatty tissue.

45:43

Here's the abnormal situation, hypo mass like area.

45:48

And what's important is when you're scanning this transverse

45:51

line hearts that you scan distally as well saying

45:56

perpendicular to the metatarsal heads and going distally.

45:59

Again, that's where the,

46:00

where the aroma is of the three steps.

46:02

This one is the least accurate, right?

46:05

Then go to step two looking long axis.

46:08

And that's where I wanna show exactly what I mentioned.

46:11

The, the aroma is going over the edge of the ligament.

46:15

The bursa is more proximal and dorsal and more an coic

46:18

but through transmission in most scenarios.

46:21

Here's an on MRI, there's an aroma, there's the bura.

46:25

They are different locations and they look differently.

46:30

Here's a companion case.

46:31

Here's the transverse metatarsal ligament.

46:34

Thema the nerve going into it. And here's the birthstone.

46:37

And again, this is minimally, there's minimal fluid.

46:39

This is not even concurred bursitis based on the size at

46:43

least 'cause you're allowed up to three millimeters

46:47

and uh, menial lateral to be considered normal.

46:50

Then finally, step three,

46:51

the most important molder maneuver.

46:53

This is a clinical sign

46:54

that if you squeeze the foot from side to side,

46:57

that there'll be a painful click

46:58

of the neuroma moving in a plantar direction.

47:01

Here's what we're looking at. There's the aroma.

47:04

This is normal. As we squeeze from side to side,

47:08

what we're seeing is plantar displacement of the neuroma.

47:12

That's why I scan plantar. I'm looking for three things.

47:16

One, you see the neuroma moving, you feel the click.

47:21

And three, are you reproducing the symptoms via all three?

47:24

You're a hundred percent accurate,

47:25

but look how better we can see this neuroma

47:29

and we can measure it accurately.

47:31

The bursa will not do this. Why?

47:33

Because it's held in a al location by the transverse

47:37

metatarsal ligament.

47:38

So again, the anatomy is key to understanding the difference

47:41

between a neuroma and a bura.

47:43

Finally, last slide before the summary here.

47:47

Remember peri capsular fibrosis related

47:49

to PLA plantar plate injury.

47:51

It can simulate CC an MR perhaps in aroma,

47:55

although we wouldn't fall into that pitfall.

47:57

We can see that the capsule here is missing it's ated,

48:00

it's form compared to here where it merged

48:03

with the plantar plate and

48:04

by ultrasound it's really hugging the metatarsal

48:08

point and not in between.

48:10

Importantly, you would not have a positive molders maneuver

48:14

with periocular fibrosis.

48:18

Come point entrapment.

48:19

They occurred specific areas, the hallmark edema

48:22

and enlargement at en proximal the entrapment site.

48:26

Next thing, when you push on the emus nerve,

48:29

they will tell you you're in the right location.

48:32

Reproducing symptoms. This compliments

48:34

electrodiagnostic testing.

48:36

I've highlighted the use

48:37

of dynamic imaging looking at snapping ulnar,

48:40

nerve snapping tricep syndrome,

48:42

also the molder maneuver in the foot as well.

48:45

And the final point, although I'm highlighting the locations

48:49

of entrapment neuropathy,

48:51

you should scan the entire nerve in the

48:53

extremity in short axis.

48:55

It takes a minute to do. It's so easy.

48:58

The reason is, although clinically

49:00

it may be suspected someone has an entrapment neuropathy,

49:04

you could have a nerve, the nerve sheath tumor

49:07

or something, uh, in other locations.

49:10

So you may start at an entrapment site,

49:13

but you should scan the entire nerve to cover everything

49:16

between the entrapment sites in short axis.

49:18

That can be done very efficiently.

49:21

Again, with this QR code is gets you to where my, uh,

49:26

syllabus material is.

49:27

There's all, there's other educational material,

49:30

usually ultrasound things you can consider

49:32

looking to that if you wish.

49:34

I wanna thank you very much for your attention

49:35

and now I can take some questions.

49:38

Yes, thank you so much Dr. Jacobson.

49:41

At this time we will open the floor

49:42

for any questions from our audience

49:44

and you may submit your questions

49:45

through the q and a feature.

49:51

Uh, the first one is share the PDF, uh,

49:53

hopefully you got that QR code.

49:56

Um, I can put try one more time if you like.

50:01

I'll see if there's any other questions

50:02

that pop up in the meantime.

50:12

Okay, well I'm not seeing any questions.

50:17

That's either a good sign or a bad sign.

50:20

I presume it's a good sign.

50:21

So thorough. So thorough that everyone's like, yeah, I

50:24

Understand. So what I,

50:25

on my website Ms. My is my email.

50:27

You can email me any questions and I can,

50:29

and I can answer anything, uh, offline, not offline,

50:33

but outside of this, this webinar. Okay,

50:36

Well awesome. Thank you

50:37

so much again for sharing your lecture with us.

50:39

Uh, Dr. Jacobson, oh,

50:41

a question did just pop in into the q and a. If you got

50:45

Oh, I, I almost got out of it.

50:47

Okay. Which peripheral nerve entrapment is most difficult

50:50

to diagnose and I think anterior interosseous nerve is

50:55

by far the most because the nerve is small

50:58

and the muscle is so, uh, epigenic from the effect of that

51:02

that I just can't, I can't penetrate to it.

51:05

That by far is the most difficult.

51:09

The easiest would be the one

51:10

where the nerves are most enlarged would be number one,

51:12

cual tunnel number two carpal tunnel.

51:15

Uh, I think, uh, tarsal tunnel is challenging

51:18

'cause the nerve looks normal, but you just have

51:19

to keep looking all around for a ganglion cyst some other

51:22

cause those are the ones that really come to mind.

51:27

The, the interal aroma is challenging,

51:30

but that's why I feel

51:31

that molar maneuver really helps save the day on that one.

51:34

So that's just some information on my feeling on the most

51:37

difficult, uh, nerves to scan for entrapment.

51:44

Alright, well thank you so much Dr. Jacobson

51:47

and thank you to everyone

51:48

for participating in our noon conference

51:50

and asking, uh, two questions.

51:53

Thank you so much. Uh, you can access the recording

51:55

of today's conference and all our previous noon conferences

51:57

by creating a free account.

51:59

We'll also email out a link to the replay later today.

52:03

Be sure to join us on Thursday,

52:05

April 3rd at 12:00 PM Eastern Word.

52:08

Dr. Mark Goslin will deliver a lecture entitled Conceptual

52:12

Approach to the Pleura.

52:13

You can register for it@mrionline.com

52:16

and follow us on social media

52:17

for updates on future noon conferences.

52:19

Thanks again and have a great day.