nerve adaptation in response to mechanical loading_marko bodor

8/18/2019 Nerve Adaptation in Response to Mechanical Loading_Marko Bodor

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Nerve Adaptation in Response to

Mechanical Loading

Marko Bodor MD

Physical Medicine and Rehabilitation,

Spine and Sports MedicineNapa, California

Voluntary Assistant Professor

Departments of Neurological Surgery

University of California San FranciscoPhysical Medicine and Rehabilitation

University of California Davis


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Disclosure

No disclosures relative to the current

presentation.


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Skin

Skin adapts to mechanical loading by

getting thicker .


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Muscle

Muscles adapt to mechanical loading by

getting larger.


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Bone

Bones adapt to mechanical loading by

increasing in thickness and diameter.

From Ireland A et al

Med Sci Sports 2013


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Nerve

Do nerves adapt to mechanical loading?


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Tires

How is it that a 2000 kg car has tires that

need only 2.5 ATM pressure while those of

an 80 kg bicycle/rider require 5 ATM?


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Larger

tires

allow

lower

tire

pressures.

1) 2.5 ATM ≈ 2.5 kg force/cm2.

2) Contact area = 20 x 25 cm

= 500 cm2.

3) 2.5kg/cm2 x 500 cm2 =1250 kg.

4) 4 tires x 1250 kg/tire = 5000

kg support for the car.

1) 5 ATM ≈ 5 kg force/cm2

2) Contact area = 3 x 5 cm =

15 cm2.

3) 5 kg/cm2 x 15 cm2 = 75kg.

4) 2 tires x 75 kg/tire = 150

kg support for bike & rider


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Tire‐Nerve Analogy

Larger nerves will have lower intraneural

pressure for the same externally applied load.

100 gm load on a 5 mm2 nerve = 20 gm/mm2 ≈ 200 kPa

100 gm load on a 10 mm2 nerve = 10 gm/mm2 ≈ 100 kPa


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Evidence

for

Nerve

Enlargement

#1

Gitlin G Concerning the gangliform enlargement

(pseudoganglion) on the nerve to the teres minor

muscle. J Anat 1957.


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Nerve

enlargement

observed

in

26/36normal cadavers at quadrangular space

Gitlin G Concerning the gangliform enlargement

(pseudoganglion) on the nerve to the teres minor

muscle. J Anat 1957.


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Evidence

for

Nerve

Enlargement

#2

Neary D, Ochoa J, Gilliat RW. Subclinical

entrapment neuropathy in man. J Neurol Sci 1975

P6

ME

D4

Ulnar nerve

enlargement

seen at medial

epicondyle (ME)

in 12/12cadavers:


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Evidence

for

Nerve

Enlargement

#2



P6

ME

D4

7/12 – no

pathologicchanges

5/12 – bulbous

swellings and

intercalated

segments.


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Evidence

for

Nerve

Enlargement

#3



P6

ME

D4

Median nerve

enlargementseen at flexor

retinaculum in

12/12 cadavers:

Renaut bodies ( RB )

seen in all nerves at

level of retinaculum

RB

RBRB


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Evidence

for

Nerve

Enlargement

#3



P6

ME

D4

7/12 - no

pathologicchanges

5/12 – bulbous

swellings andintercalated

segments

RB

RBRB


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Evidence

for

Nerve

Enlargement

#4

Visser LH, Smidt MH, Lee ML. Diagnostic value of

wrist-forearm ratio in carpal tunnel syndrome

P6

ME

D4

Wrist-forearm ratio:

1.6 in 89 controls

2.4 in 161 patients

with CTS


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Evidence

for

Nerve

Enlargement

#4

Visser LH, Smidt MH, Lee ML. Diagnostic value of

wrist-forearm ratio in carpal tunnel syndrome

P6

ME

D4

Therefore:

It is normal for

median nerves to be

enlarged up to 1.6x

at the wrist.


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Evidence

for

Nerve

Enlargement

#5

Bodor M, McAuliffe M, Derrington S, Uribe Y. – preliminary

unpublished data

P6

D4

Median Palmar Cutaneous Nerve enlargement

between the wrist and palm - Case #1:

Wrist - 0.6 mm2Palm – 1.8 mm2


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Evidence

for

Nerve

Enlargement

#5

Bodor M, McAuliffe M, Derrington S, Uribe Y. Preliminary

unpublished data

P6

D4

Median Palmar Cutaneous Nerve enlargement

between the wrist and palm - Case #2:

Wrist - 0.9 mm2 Palm – 2.4 mm2


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Evidence

for

Nerve

Enlargement

#5

Bodor M, McAuliffe M, Derrington S, Uribe Y. Preliminary

unpublished data.

P6

D4

Limitations:

- Two cases shown were weight-lifters - predisposing

to MPCN enlargement at the palm.

- Presence of enlargement has been inconsistent

among other subjects.

- MPC has a variable course and may enlarge slightlynext to FCR tendon in wrist.


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Is there a point at which nerve

enlargement becomes maladaptive?

P6

D4


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Median Nerve DML vs CSA at Carpal Tunnel

among Controls (□) and Patients (○)

Adapted from Fujimoto K et al. Diagnosis of severe

carpal tunnel syndrome using electrodiagnosis and

sonography. Ultrasound Med Biol 2015 Oct.

P6

ME


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Ulnar Nerve NCV vs. Diameter

among UNE Patients

P6

D4

Adapted from Beekman R et al. Clinical, electrodiagnostic

and sonographic studies at the elbow. Muscle & Nerve

2004.


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Which graph shows a better correlation

between

Nerve

Size

and

Velocity?

Median (Fujimoto 2015) Ulnar (Beekman 2004)

Note Difference in Population and Parameters!

CSA and DML for Median, Diameter and NCV for Ulnar.

P6

ME


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Which graph shows a better correlation

between

Nerve

Size

and

Velocity?

Median (Fujimoto 2015) Ulnar (Beekman 2004)

Note Difference in Population and Parameters!

CSA and DML for Median, Diameter and NCV for Ulnar.

P6

ME 1

/ N C V


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Conclusions:

Nerve enlargement can occur in the absence

disease at locations of mechanical stress

susceptible to compression neuropathies.

Nerve enlargement can be a normal adaptive

response which reduces intraneural pressure.

Nerve enlargement within the confines of a bony

space such as the carpal tunnel or spinal canal

becomes maladaptive after a certain point.

Disclaimer: Not all enlargement is adaptive - it

can be secondary to disease.


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Nerve Adaptation - Flattening

6

N 6

N


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Nerve Adaptation - Flattening

222

3 3

3 3

2 2 2

1.5

6

N 6

N

1.5 1.5 1.5


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Lateral Femoral CutaneousNerve


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Sciatic Nerve


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Median compression at proximal retinaculum

with severe flattening of nerve.


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nerve adaptation in response to mechanical loading_marko bodor

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