10: MSK Growth, Injury and Repair - Peripheral Nerve Injuries

Question 1

what is a motor unit (efferent) composed of?

Answer 1

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

Question 2

what is a sensory unit composed of?

Answer 2

• cell bodies in posterior root ganglia
• i.e. lie outside the spinal cord

Question 3

what is a peripheral nerve?

Answer 3

• the part of a spinal nerve distal to the nerve roots
• a bundle of nerve fibres

Question 4

Answer 4

Question 5

what is the function of A-alpha, group IA and IB afferent fibre types?

Answer 5

large motor axons
muscle stretch and tension
sensory axons

Question 6

what is the function of A-beta group II afferent fibres?

Answer 6

touch, pressure, vibration and joint position sensory axons

Question 7

what is the function of A-gamma fibres?

Answer 7

gamma efferent motor axons

Question 8

what is the function of A-delta group III afferent fibres?

Answer 8

• sharp pain
• very light touch
• temperature sensation

Question 9

what is the function of B fibres?

Answer 9

sympathetic preganglionic motor axons

Question 10

what is the function of C Group IV afferent fibres?

Answer 10

• dull, aching, burning pain
• temperature sensation

Question 11

compression/entrapment of peripheral nerves: list some classical conditions

Answer 11

• carpal tunnel syndrome > median nerve at wrist
• sciatica > spinal root by intervertebral disc
• Morton’s neuroma > digital nerve in 2nd or 3rd web space of forefoot

Question 12

describe neurapraxia

Answer 12

• Neurapraxia is the mildest form of peripheral nerve injury commonly induced by focal demyelination or ischemia.
• In neurapraxia, the conduction of nerve impulses is blocked (reversible).
• nerve in continuity

Question 13

describe axonotmesis

Answer 13

• more severe than neurapraxia
• peripheral nerves become damaged due to stretch or crushed or indirect blow
• the endoneurium remains intacts (tube in continuity), but there is a disruption of axons.
• prognosis if fair

Question 14

describe neurotmesis

Answer 14

• complete division of a peripheral nerve, caused by laceration or avulsion
• no recovery unless repaired by direct suturing or grafting
• endoneural tubes disrupted so high change of ‘miswiring’ suring regeneration
• prognosis is poor

Question 15

what Sunderland grade is a neurapraxia?

Answer 15

grade 1

Question 16

what sunderland grade is a axonotmesis?

Answer 16

grade 2

Question 17

what sunderland grade is a neurotmesis?

Answer 17

grade 3-5 depending on severity

Question 18

closed nerve injuries are associated with

Answer 18

• nerve injuries in continuity such as neuropraxis or axonotmesis
• typically stretching of nerve: brachial plexus injuries and radial nerve humeral fracture

Question 19

when is surgery indicated for a closed nerve injury?

Answer 19

after 3 months if no recovery is identified clinically or by electromyography

Question 20

what is the axonal growth rate?

Answer 20

1-3 mm/day

Question 21

open nerve injuries are typically associated with?

Answer 21

nerve division > neurotmesis
e.g. knives/glass

Question 22

how are open nerve injuries treated?

Answer 22

early surgery

Question 23

In an open nerve injury, the distal portion of the nerve undergoes which type of degeneration?

Answer 23

Wallerian
- occurs up to 2-3 weeks post injury

Question 24

what are some clinical features of a nerve injury?

Answer 24

sensory:
- dysaethesiae (disordered sensation): anaesthetic (numbness), hypo & hyper-aesthetic, paraesthetic (pins and needles)

motor:
- paresis (weakness) or paralysis +/- wasting
- dry skin
- loss of tactile adherence since sudomotor nerve fibres not stimulating

reflexes: diminished or absent

Question 26

describe the healing process of a nerve injury

Answer 26

Starts with initial death of axons distal to site of injury:
- Wallerian degeneration
- then degredation of myelin sheath

• proximal axonal budding occurs after about 4 days.
• regeneration proceeds at a rate of about 1mm/day (can be 3-5mm in children).
• pain is first modality to return.

Question 27

the prognosis for nerve injury recovery depends on…

Answer 27

whether the nerve is:
- ‘pure’ (only sensory or only motor)
- ‘mixed’ (sensory and motor within same nerve)

• how distal the lesion is (proximal worse)

Question 28

which sign can be used to monitor nerve injury recovery?

Answer 28

Tinel’s sign
- (tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed.

Question 29

how can a nerve injury be assessed, and recovery monitored?

Answer 29

by electrophysiological nerve conduction studies

Question 30

when is a direct repair of a nerve injury indicated?

Answer 30

• laceration
• no loss of nerve tissue

Question 31

when is nerve grafting indicated?

Answer 31

nerve loss
- late repair (retraction, sural nerve)

Question 32

describe the ‘rule of three’ surgical timing in a traumatic peripheral nerve injury

Answer 32

• immediate surgery within 3 days for clean and sharp injuries
• early surgery within 3 weeks for blunt/contusion injuries
• delayed surgery, performed 3 months after injury, for closed injuries

Question 33

how do you tell the difference between a peripheral or central nerve lession (UMN vs LMN)?

strength, tone, deep tendon reflexes, clonus, Babinski’s sign, atrophy

Answer 33