Nerve Injury and Repair

Question 1

What technical advancement has allowed routine attempts at surgical repair of nerves in the 20th century?

Answer 1

The availability of surgical microscopes

Question 2

What is the most basic subunit of the peripheral nerve?

Answer 2

The Axon

Question 3

What is each axon surrounded by?

Answer 3

Endonurium

Question 4

Axons are grouped into what unit?

Answer 4

Fascicles

Question 5

What makes up the interfascicular space?

Answer 5

Epineurium

Question 6

The main nerve is surrounded by what sheath?

Answer 6

The external epineurial sheath

Question 7

What is the name of the external connective tissue that holds the blood supply to peripheral nerves and allows gliding during normal range of motion?

Answer 7

Mesoneurium

Question 8

Why do distal nerve repairs correlate to better functional status?

Answer 8

Proximally, fascicular topography allows significant intermingling of sensory and motor fibers, but as you move distally in a nerve, the fascicles become more distinctly grouped/differentiated

Question 9

After nerve injury, what happens to the proximal portion of the nerve?

Answer 9

It dies back to the nearest node of Ranvier and eventually regrows from multiple “growth cones” in an attempt to grow into the distal endoneurial tube

Question 10

After nerve injury, what happens to the distal portion of the nerve?

Answer 10

It undergoes Wallerian degeneration, where the myelin sheath and debris are phagocytosed and the axon is replaced over 3-6 weeks - it is capable of accepting new axon sprouts

Question 11

Why are the first 72 hours important in a nerve injury

Answer 11

The distal nerve can still transmit electrical stimulation and can be located with electrical stimulation in the OR

Question 12

What are the zones of injury in a nerve

Answer 12

Neurapraxia, axonotmesis, and neurotmesis

Question 13

What is Neurapraxia?

Answer 13

The least severe zone of nerve injury (scalpel injury, for example) which heals in das to months without intervention

Question 14

What is Axonotmesis?

Answer 14

The second most severe nerve injury - depending on degree, may have complete or no recovery without intervention, since wallerian degeneration takes lace and recover is based on on degree of scar tissue within endoneurial or perineurial sheaths

Question 15

What is Neurotmesis?

Answer 15

The third and most severe degree of nerve injury, for which only operative repair or grafting will result in recovery

Question 16

How quickly do axons grow?

Answer 16

1 inch per month or 1mm per day

Question 17

What are the benefits of exploring an open nerve injury immediately?

Answer 17

1. Identification of distal nerve with electrical stimulation, 2. Primary repair of nerve is possible, 3. Tagging nerves for later definitive repair, when injury has declared itself, so as to avoid suturing through scar

Question 18

How do you deal with nerve injury in a closed wound

Answer 18

Close follow up, as it may just be neurapraxia and self limited. Monitor with non-invasive testing over weeks to months

Question 19

What timeline is there for definitive motor neuron repair?

Answer 19

4-6 months, to allow regenerating axons time to grow into target muscle

Question 20

How do you deal with nerve injuries from gunshot wounds?

Answer 20

Treat as closed injury - most of the time, it is neurapraxia or axonotmesis from blast injury

Question 21

What is nerve ending preparation?

Answer 21

Adequate resection of damaged portion of nerve until a flush, healthy fascicular pattern is identified - ley yeux d’escargot (eyes of a snail) - so that the fascicular bundles align on repair

Question 22

True/False: It is acceptable to do a nerve graft to avoid a repair with tension

Answer 22

True - it is essential that there by no tension whatsoever in a nerve repair

Question 23

What is epineurial nerve repair?

Answer 23

Suturing only the external epineurial vessels with the fascicles aligned

Question 24

What is grouped fascicular repair of a nerve?

Answer 24

Suturing internal epineurium together when excellent fascicular topography is visualized

Question 25

What is the downside of grouped fascicular repair

Answer 25

Reports show more intraneural scarring

Question 26

What are the options in treating nerve gaps during nerve repair?

Answer 26

1. Interpositional nerve grafting, or 2. Commercially available bioabsorbable nerve conduits

Question 27

What advantages are there to bioabsorbable nerve conduits?

Answer 27

In 3cm or shorter nerve gaps, there is better 2 point discrimination, as compared to grafts or primary repairs, in digital nerve injuries

Question 28

What is nerve conduit entubulation?

Answer 28

Placing part of the proximal and distal nerve inside the nerve conduit to direct normal nerve regeneration

Question 29

Other than commercially available nerve conduits, what else may serve as a nerve conduit?

Answer 29

Veins, though this often breaks down

Question 30

Why are interposition nerve grafts reversed?

Answer 30

So axons do not get “lost” down normal nerve branches in the interposed segment

Question 31

What do you do for nerve compression?

Answer 31

Neurolysis- decompression of the nerve; resection and grafting not required

Question 32

What is a nerve transfer?

Answer 32

Using redundant fascicles to reinnervate after a nerve injury

Question 33

What would nerve transfer ever be done?

Answer 33

Some injuries (brachial plexus, for example) with traditionally poor outcomes also have anatomy that would allow faster reinnervation with transfers

Question 34

What is the normal postoperative management of a nerve repair?

Answer 34

Splint 7-10 days in position of function; range of motion increased gradually over 6-8 weeks; neurontin for neuropathy; sensory and motor reeducation