Peripheral nerve injury

Question 1

What is peripheral nerve?

Answer 1

• The part of a spinal nerve distal to the nerve roots.
• Bundles of nerve fibres.
• Range in diameter from 0.3-22 μm.
• Schwann cells form a thin cytoplasmic tube around
• Larger fibres in a multi-layered insulating membrane (myelin sheath).
• Multiple layers of connective tissue surrounding axons

Question 2

In what ways can the peripheral nerves be injured?

Answer 2

• Compression
• Trauma
  
  • Neurapraxia
  • Axonotmesis
  • Neurotmesis

Question 3

List and explain some of the classical nerve compression injuries.

Answer 3

1. Carpal tunnel syndrome
   
   • Median nerve at wrist is effected
2. Sciatica
   
   • Spinal root by intervertebral disc effected
3. Morton’s neuroma
   
   • Digital nerve in 2nd or 3rd web space of forefoot

Question 4

What is neurapraxia?

Answer 4

• Microcirculation is bruised
• lose a bit of myelin
• short distance
• Everything beyond is still intact so there is a good chance of recovery

Question 5

What is axonotmesis?

Answer 5

• Axon itself is damaged itself
• Wallerian degeneration follows: everything distally dies, the nerve itself will retract back a little – can regrow back down the tunnel – so prognosis is actually okay

Question 6

What is neurotmesis?

Answer 6

• Whole nerve is cut, no longer a connection between the nerve
• Laceration or pulled apart
• Nerve distally dies, nerve comes to end of tunnel and doesn’t know where to go – so it sprouts everywhere creating a neuroma, rather than going along tunnel correctly
• Sensory nerves have better prognosis than mixed nerves

Question 7

What is a closed nerve injury?

Answer 7

• Associated with nerve injuries in continuity
• Spontaneous recovery if possible
• Surgery indicated after 3 months
• Axonal growth rate (1-3mm per day)

Question 8

What is an open nerve injury?

Answer 8

• Frequently related to nerve division
• Treated with early surgery
• Distal portion of nerve will undergo Wallerian degeneration
• There can still be some sensation up to 12 hrs post cut of nerve, thinking that a clot conducts – but after 12hrs there will be loss of sensation

Question 9

What are the features of sensory loss?

Answer 9

• Dysthesiae (disordered sensation)
  
  • Anaesthetic (numb), hypo and hyper-aesthetic, paraesthetic (pins and needles )
• Motor
  
  • paresis (weakness) or paralysis +/- wasting
  • dry skin
• Reflexes
  
  • diminished or absent

Question 10

Explain the healing process of nerves.

Answer 10

• it is very slow!!

1. Initial death of axons distal to site of injury
   
   • Wallerian degeneration
   • Then degeneration to myelin sheath
2. Proximal axonal budding occurs after about 4 days
3. Regeneration proceeds at about 1mm/day [poss. 3-5mm in kids]
4. Pain if first modality to return

Question 11

What does the prognosis of healing depend on?

Answer 11

Whether nerve is:

• Pure
• Mixed

And how distal the lesion is [proximal is worse]

Question 12

How can we monitor healing?

Answer 12

Tinnels sign

Electrophysiological Nerve Conduction Studies

Question 13

When is direct nerve repair appropriate?

Answer 13

• Laceration
• No nerve tissue loss
• Microscope
• Bundle repair

Question 14

When are nerve grafts appropriate?

Answer 14

• Nerve loss
• Late repair

Question 15

What is the “Rule of Three” in nerve repair?

Answer 15

Surgical timing in a traumatic peripheral nerve injury

• 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 16

How can we tell the difference between central (UMN) or peripheral nerve injury (LMN)?

Answer 16