Peripheral Nerve Injuries

Question 1

Which cells form a thin cytoplasmic tube around peripheral nerves?

Answer 1

Schwann cells

Question 2

What is the name of the membrane that coats the axon of the nerve?

Answer 2

Endoneurium

Question 3

What is the name of the membrane that coats the fascicle of the nerve?

Answer 3

Perineurium

Question 4

What is the name of the membrane that coats the nerve?

Answer 4

Epineurium

Question 5

Nerve fascicles are bundles of what?

Answer 5

Axons

Question 6

What does a bundle of fascicles form?

Answer 6

Nerve

Question 7

What is the fiber category with the fastest conduction speed?

Answer 7

Aα

Question 8

What is the thinnest fiber category?

Answer 8

C

Question 9

Which nerve fiber category carries sharp pain, very light touch and temperature sensation?

Answer 9

Aδ

Question 10

What type of sensations do category C nerve fibers carry?

Answer 10

Dull, aching, burning pain and temperature sensation

Question 11

Which nerve fiber category carries touch, pressure, vibration and joint position sensory axons?

Answer 11

Aβ

Question 12

What is neurapraxia?

Answer 12

Temporary loss of motor and sensory function due to blockage of nerve conduction, lasting six to eight weeks before full recovery - often from blunt trauma or shock injuries. Nerve remains intact.

Question 13

What is axonotmesis?

Answer 13

Peripheral nerve injury in which the axons and their myelin sheath are damaged but the endoneurium, perineurium and epineurium remain intact. Usually the result of a more severe crush or contusion than neurapraxia, mainly follows a stretch injury.

Question 14

What is neurotmesis?

Answer 14

Peripheral nerve injury in which both the nerve and nerve sheath are disrupted - partial recovery may occur but complete recovery is impossible.

Question 15

What are three classical conditions of nerve compression?

Answer 15

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 16

Can peripheral nerves regenerate?

Answer 16

Yes

Question 17

In a closed peripheral nerve injury, when is surgery indicated?

Answer 17

If no recovery identified after 3 months

Question 18

What are the symptoms of a nerve injury?

Answer 18

Dysaethesiae (disordered sensation)
- anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)
Paresis (weakness) or paralysis +/- wasting
Dry skin
- loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
Reflexes diminished or absent

Question 19

What is Wallerian degeneration?

Answer 19

Active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. further from the neuron’s cell body) degenerates. (Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event.)

Question 20

At what rate does nerve regeneration proceed?

Answer 20

~ 1 mm/day

Question 21

Which is the first modality to return in recovery from a nerve injury?

Answer 21

Pain

Question 22

What is Tinel’s sign?

Answer 22

Distal tingling on percussion of the site of a damaged nerve

Question 23

What is the ‘rule of three’ in surgical timing in a traumatic peripheral nerve injury?

Answer 23

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 24

What are the differences in clinical findings between upper motor neuron lesions and lower motor neuron lesions? (tone, deep tendon reflexes, clonus, Babinki’s sign, atrophy)

Answer 24

Tone - UMN increased LMN decreased
Deep tendon reflexes - UMN increased LMN decreased
Clonus - UMN present LMN absent 
Babinki's sign - UMN present LMN absent 
Atrophy - UMN absent LMN present