Peripheral Nerve Injuries

Question 1

What is a motor unit?

Answer 1

Anterior horn cell, motor axon and muscle fibres

Question 2

What are spinal nerves?

Answer 2

Anterior and posterior roots combine to form a spinal nerve
Exit vertebral column via intervertebral foramen

Question 3

Describe a peripheral nerve

Answer 3

Range in size - 0.3-22um
Schwann cells form thin tube around
Larger fibres in a multi-layered insulated membrane (myelin sheath)
Multiple layers of CT surrounding axons

Question 4

Describe the structure of a peripheral nerve

Answer 4

Highly organised structure comprised of nerve fibres, blood vessels, and CT
Axons are coated in endoneurium
Fascicles covered in perineurium
Nerve covered on epineurium

Question 5

What increases when size of fibre increases?

Answer 5

Speed of transmission

Question 6

Describe A-alpha fibres

Answer 6

Size - 15 microns
Speed - 60-100 m/sec
Large motor axons - muscle stretch and tension sensory axons

Question 7

Describe A-beta fibres

Answer 7

Size - 12-14 microns
Speed - 30-60m/sec
Touch, pressure, vibration, and joint position - sensory axons

Question 8

Describe A-gamma fibres

Answer 8

Size - 8-10 microns
Speed - 15-30 m/sec
Gamma efferent motor axons

Question 9

Describe A-delta fibres

Answer 9

Size - 6-8 microns
Speed - 10-15m/sec
Sharp pain, very light touch and temp. sensation

Question 10

Describe B fibres

Answer 10

Size - 2-5 microns
Speed - 3-10m/sec
Sympathetic preganglionic motor axons

Question 11

Describe C fibres

Answer 11

Size - <1 microns
Speed - <1.5m/sec
Dull, aching, burning pain and temp. sensation

Question 12

What are the causes of nerve injury?

Answer 12

Compression
Trauma - direct and indirect
Neuropraxia
Axonotmesis
Neurotmesis

Question 13

What are classical conditions from compression of nerve?

Answer 13

Carpel tunnel syndrome - median nerve at wrist
Sciatica - spinal root by intravertebral disc
Morton’s neuroma - 2nd and 3rd space of forefoot digital nerve

Question 14

Describe neurapraxia

Answer 14

Nerve in continuity
Stretched or bruised
Reversible conduction block from local ischaemia and demyelination
Prognosis good

Question 15

Describe axonotmesis

Answer 15

Endoneurium intact but disruption of axons - more severe
Stretched, direct blow or crushed
Wallerian degeneration follows
Prognosis fair - sensory often better than motor

Question 16

Can peripheral nerves regenerate?

Answer 16

Yes

Question 17

Describe neurotmesis

Answer 17

Complete nerve division
Laceration or avulsion
No recovery unless repaired (suturing or grafting)
Prognosis poor
As endoneural tubes disrupted then high chance of miswiring

Question 18

What are closed nerve injuries associated with?

Answer 18

Nerve injuries in continuity - neuropraxias and axonotmesis (whole nerve still intact)

Question 19

Describe closed nerve injury

Answer 19

Spontaneous recovery is possible
Surgery indicated after 3 months - if no recovery then clinical and EMG
Axonal growth rate is 1-3mm/day

Question 20

What are examples of cloased nerve injury?

Answer 20

Brachial plexus injury
Radial nerve humeral fracture

Question 21

What is open nerve injury related to?

Answer 21

Nerve division - neurotmesis injury - ex. knives and glass

Question 22

Describe open nerve injury

Answer 22

Treated with early surgery
Distal portion of nerve undergoes Wallerian degeneration - occurs 2-3 weeks after injury

Question 23

What are the clinical features of nerve injury?

Answer 23

Sensory - dysesthesia (disordered sensation) includes anaesthetic and paraesthetic
Motor - paresis or paralysis/ wasting , and dry skin (fibres not stimulating sweat glands)
Reflexes - diminished or absent

Question 24

Describe nerve healing

Answer 24

Very slow
Starts with initial death of axons distal to site of injury - Wallerian degeneration then myelin sheath degeneration
Proximal axonal budding starts after 4 days

Question 25

What is the regeneration rate of a nerve?

Answer 25

1mm/ day
Pain is fist modality to return

Question 26

What does the prognosis for recovery depend on?

Answer 26

Pure or mixed nerve
Pure is better prognosis as always grow down to nerve plate even if not correct one
Mixed are variable (sensory and motor can grow down wrong tube)
More proximal then worse

Question 27

What is Tinel’s sign?

Answer 27

Tap over site of nerve and paraesthesia will be felt as far as distally as regeneration has progressed - used to monitor recovery

Question 28

How can injury be assessed and recovery monitored?

Answer 28

Electrophysiological nerve conduction studies

Question 29

When is direct nerve repair done?

Answer 29

Laceration and no loss of nerve tissue
Is under microscope
Is a bundle repair - helps dock tubes to match with end plates

Question 30

When is nerve grafting used?

Answer 30

Nerve loss and late repair
Use sural nerve - creates a passage for axons to grow down

Question 31

What are the findings of UMN lesions?

Answer 31

Strength decreased, tone increased, deep tendon reflexes increased, clonus present, Babinski’s sign is present and atrophy absent

Question 32

What are some findings of LMN lesion?

Answer 32

Decreased strength, decreased tone, decreased reflexes, absent clonus and Babinski’s sign, and atrophy is present