Nerve Growth & Repair

Question 1

What are the layers of a peripheral nerve?

Answer 1

Axons covered in endoneurium
Fascicles covered in perineurium
Nerves covered in epineurium

All covered in a myelin sheath by schwann cells

Question 2

Which are the fastest nerves?

Answer 2

Aalpha

Large motor axons + muscle stretch/tension sensory axons

Question 3

What are the 2nd fastest nerves?

Answer 3

Abeta

Carry innocuous sensation e.g. touch, pressure, vibration and proprioception

Question 4

What are the 3rd and 4th fastest nerves?

Answer 4

Agamma - Gamma Efferent motor neurons

Adelta - Carry sharp pain & heat

Question 5

What do B fibres carry?

Answer 5

Sympathetic motor axons (2nd slowest type)

Question 6

What do C fibres carry?

Answer 6

Dull/ache pain
burning pain
Cold

Question 7

What are the types of nerve injury?

Answer 7

Compression
Trauma:
- Direct e.g. blow or laceration
- Indirect e.g. Avulsion or traction

These result in:
- Neurapraxia
- Axonetmesis
- Neurotmesis

Question 8

What type of nerve injury are carpal tunnel, sciatica & Morton’s neuroma?

Answer 8

Compression injuries

Question 9

Define Neurapraxia?

Answer 9

Nerve is unbroken but stretched or bruised

Local ischaemia –> reversible conduction block

Question 10

Define Axonetmesis?

Answer 10

Endoneurium still intact but axons are damaged resulting in Wallerian degeneration

Recovery is rarely full but sensory is better than motor

Question 11

Define Neurotmesis?

Answer 11

Complete nerve division due to avulsion or laceration

Requires suturing/grafting for any recovery and prognosis is poor

Question 12

A closed nerve injury is neuropraxis or axonotmesis where the nerve sheath is intact. How do we handle them?

Answer 12

Spontaneous recovery is possible

Do surgery if no recovery is identified by EMG or clinically after 3 months

Question 13

What type of nerve injury are common with brachial plexus injuries and humeral fractures?

Answer 13

Closed

Question 14

An open nerve injury is usually a knife or glass that divides the nerve –> Neurotmesis. How do we handle them?

Answer 14

Early surgery

Question 15

What are the consequences of a nerve injury? (I.e. the symptoms/signs)

Answer 15

Dysaesthesia

Paresis, paralysis +/- wasting

Dry Skin

Loss of reflexes

Question 16

Wallerian degeneration is when the distal axon dies following injury, how long does it take for proximal axonal budding to occur?

Answer 16

~4 days

Question 17

How fast do nerves regrow?

Answer 17

1mm/day (1inch/month)

Pain is the first modality to return

Question 18

How might you monitor a nerve’s regrowth?

Answer 18

• Tinnel’s Sign
• Nerve Conduction studies

Question 19

When would we do direct nerve repair vs nerve grafting?

Answer 19

Direct repair if the tissues still there and we get in early. Can use growth factors as well

Grafting if the nerve is lost or late repair. often use sural nerve

Question 20

When referring to the timing of a nerve injury what do we mean by “the rule of three”?

Answer 20

• Clean or sharp? = immediate surgery within 3 days
• Blunt or contusion? = Early surgery within 3 wks
• Closed injury? = Delayed surgery within 3 months

Question 21

We need to know if an injury is peripheral or central, how would you spot UMN vs LMN?

Answer 21

UMN:
- Weaker
- Increased tone
- Increased reflexes
- Clonus
- Babinski’s

LMN:
- Weaker
- Decreased Tone
- Decreased Reflexes
- Atrophy