Peripheral Nerve Injury and Repair

Question 1

What is the process of nerve regeneration following axonotmesis?

Answer 1

1) Distal segment undergoes Wallerian degeneration
2) Schwann cells line up on basement membrane
3) After one month proximal axonal buds sprout and migrate 1mm/day

Question 2

What is the single most important factor for recovery from nerve injury?

Answer 2

1) Age (younger=better)
2) Level of transection (distal=better)
3) Lacerated vs. crush injury (lacerated=better)
4) Repair within 18 months

Question 3

What are the three main layers of a peripheral nerve?

Answer 3

1) Epineurium- covers entire nerve
2) Perineurum- cover individual fascicles
3) Endoneureum- cover individual axons

Question 4

Which peripheral nerve structures functions to cushion the nerve against external pressure?

Answer 4

Epineurium

Question 5

Which structures are slowly adapting skin receptors that detect pressure, texture, and low frequency vibration and are best evaluated by static two-point discrimination?

Answer 5

Merkel’s receptor

Question 6

What is the classification for nerve injuries?

Answer 6

Sunderland:
1st degree (neuropraxia)- myelin disrupted but axon and endoneurium intact
2nd degree (axonotmesis)- myelin and axon disrupted, endoneurium intact
3rd degree- endoneurium partially scarred
4th degree- nerve in continuity but circumferentially scarred at level of injury
5th degree (neurotmesis)

Neuropraxia and axonotmesis are reversible, neurotmesis is not

Question 7

What type of nerve injuries are group fascicular repair?

Answer 7

1) Median nerve in distal forearm
2) Ulnar nerve in distal forearm
3) Sciatic nerve in thigh

Question 8

What are indications for allograft and autograft of nerve defects?

Answer 8

Allograft: less than 5cm with a collagen conduit
Autograft: if >5cm defect

Question 9

Which nerve has the most favorable regenerative potential in restoring motor function after a graft repair within half a year after being injured?

Answer 9

radial
excellent recovery potential: the radial, musculocutaneous, and femoral nerves
moderate recovery potential: median, ulnar, and tibial nerves
nerve had poor recovery potential: the peroneal nerve

Question 10

Axon regeneration almost always occurs following a Sunderland second-degree nerve injury because which anatomic structure is not injured?

Answer 10

Endoneurium

Question 11

Which structures are slowly adapting skin receptors that detect pressure, texture, and low frequency vibration and are best evaluated by static two-point discrimination?

Answer 11

Merkel’s receptor- sustained touch
Pacinian- vibration
Meissner- touch
Ruffini- skin stretch