8. peripheral nerve injuries

Question 1

What 2 units make up peripheral nerves?

Answer 1

motor unit

• anterior horn cell (located in grey matter of spinal cord)
• motor axon
• innervates muscle fibres (neuromuscular junctions)

sensory unit

• cell bodies in posterior root ganglion
• ie lie outside spinal cord

Question 2

Where is the cell body for the motor unit of peripheral nerves?

Answer 2

• Anterior horn cell (located in grey matter of spinal cord)

Question 3

Where is the cell body for sensory unit of peripheral nerves?

Answer 3

• Cell bodies in posterior root ganglion, so lie outside spinal cord

Question 4

Explain the ventral and dorsal roots eventually forming peripheral nerves?

Answer 4

nerve fibres joint to form ventral motor roots and dorsal sensory roots, these combined to form spinal nerve

Question 5

What do spinal nerves exits the vertebral column through?

Answer 5

Intervertebral foramen

Question 6

Describe the structure of peripheral nerves from deep to superficial?

Answer 6

Axons coated with endoneurium, grouped into fascaicles (nerve bundles), covered with perineuriu, grouped to form nerve covered with epineurium

Question 7

What does nerve fibre diameters range between?

Answer 7

0.3-22um

Question 8

What forms a thin cytoplasmic tube around nerve fibres of peripheral nerves?

Answer 8

Schwann cells

Question 9

What are the different fibre types from smallest to largest?

Answer 9

Question 10

What is the speed of each fibre type?

Answer 10

Question 11

What is the function of each fibre type?

Answer 11

Question 12

How does diameter of a fibre impact speed of transmission?

Answer 12

With increasing diameter comes increasing speed of transmission

Question 13

What are the different categories of injuries to peripheral nerves?

Answer 13

Compression

Trauma

Question 14

When does compression of peripheral nerve occur?

Answer 14

Due to nerve palsies or entrapement

Question 15

What are some examples of nerve compression due to entrapment?

Answer 15

• Carpal tunnel syndrome
  
  • Median nerve at wrist
• Sciatica
  
  • Spinal root by intervertebral disc
• Morton’s neurom
  
  • Digital nerve in 2^nd or 3^rd webspace of forefoot

Question 16

What are the 3 categories of trauma injuries to peripheral nerves?

Answer 16

• neurapraxia
• axonotmesis
• neurotmesis

Question 17

Describe neurapraxia?

Answer 17

• nerve in continuity
• stretched or bruised
• reversible conduction block due to local ischaemia and demyelination
• prognosis good

Question 18

Describe axonotmesis?

Answer 18

• endoneurium intact but disruption of axons (more severe than neurapraxia)
• stretched or crushed or direct blow
• wallerian degeneration follows
• prognosis is fair

Question 19

What kind of degeneration follows axonotmesis?

Answer 19

• Wallerian degeneration follows so nerve fibre effectively disappears

Question 20

Describe neurotmesis?

Answer 20

• complete nerve division
• laceration or avulsion
• no recovery unless repaired by direct suturing or grafting
• endoneural tubes disrupted so high chance of ‘miswiring’ during regeneration, leading to large neuroma
• prognosis poor

Question 21

What is used to grade trauma to peripheral nerve?

Answer 21

Sunderland grading

Question 22

Describe the sunderland grading system?

Answer 22

Question 23

Nerve injuries can be described as open or closed, which of neuropraxis, axonotmesis and neurotmetic is each?

Answer 23

Closed - neuropraxis, axonotmesis

Open - neurotmesis

Question 24

Which of closed and open nerve injuries heals better?

Answer 24

Closed injuries - spontaneous recovery possible (better)

Open injuries - treated with early surgery

Question 25

What are closed nerve injuries typically caused by?

Answer 25

* Typically stretching of the nerve * Brachial plexus injuries * Radial nerve injuries due to humeral fractures

Question 26

What part of nerve undergoes Wallerian degeneration in open nerve injuries?

Answer 26

* Distal portion of nerve undergoes Wallerian degeneration

Question 27

What are the clinical features of peripheral nerve injuries?

Answer 27

* Dysaethesiae (disordered sensation) * Anaesthetic (numb), hypo and hyper-aesthetic paraesthetic (pins and needles) * Motor * Paresis (weakness) or paralysis with or without wasting * Dry skin * Reflexes * Diminished or absent

Question 28

What is the medical term for disordered sensation?

Answer 28

Dysaesthesia

Question 29

What is the medical term for pins and needles?

Answer 29

Paraesthesis

Question 30

What is the medical term for weakness?

Answer 30

Paresis

Question 31

Describe the healing of peripheral nerves?

Answer 31

* Slow * Starts with initial death of axons distal to site of injury * Wallerian degeneration * Then degradation of myelin sheath * Proximal axonal budding (start of growth) occurs after 4 days * Rate of growth 1-3mm/day * Tinel’s sign can monitor recovery * Tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed * Also by electrophysiological nerve conduction studies

Question 32

What is the rate of new axonal growth?

Answer 32

1-3mm/day

Question 33

How can growth of new nerves after injury be monitored?

Answer 33

* Tinel’s sign can monitor recovery * Tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed * Also by electrophysiological nerve conduction studies

Question 34

What does prognosis of peripheral nerve injuries depend on?

Answer 34

* Whether pure nerve (only sensory or motor) or mixed nerve (both sensory and motor in same nerve) * How distal the lesion is (proximal is worse)

Question 35

What are some nerve repair methods?

Answer 35

* Direct repair * Can happen due to laceration if no loss nerve tissue * Microscope/loupes * Bundle repair * Growth factors * Nerve grafting * If nerve loss has occurred * Late repair * Use sural nerve to provide tubes to connect nerve endings

Question 36

Compare and contrast UMN and LMN in terms of: - strength - tone - deep tendon reflexes - clonus - Babinski's sign atrophy

Answer 36