MSK Growth, Injury and Repair – Nerve

Question 1

What is the nature different types of nerve injury?

Answer 1

Compression (at different possible levels).

Trauma – direct (blow, laceration) or indirect (avulsion, traction) – neurapraxia, axonotmesis, neurotmesis.

Question 2

What does compression involve and what are some example conditions?

Answer 2

Nerve entrapment. Classical conditions: Carpal tunnel syndrome – median nerve at wrist; Sciatica – spinal root by IV disc; Morton’s neuroma – digital nerve in 2nd / 3rd web space of forefoot.

Question 3

Describe Neurapraxia injury and its prognosis

Answer 3

Nerve in continuity. Stretched (8% will damage microcirculation) or bruised. Reversible conduction block – local ischaemia and demyelination.
Prognosis good (weeks or months; mild).

Question 4

Describe Axonotmesis injury and its prognosis

Answer 4

Endometrium intact (tube in continuity), but disruption of axons; more severe injury. Stretched ++ (15% elongation disrupts axons) or crushed or direct blow. Wallerian degeneration follows. 
Prognosis fair (sensory recovery often better than motor; not normal but sufficient)

Question 5

Describe Neurotmesis injury and its prognosis

Answer 5

Complete nerve division. Laceration or avulsion. No recovery unless repaired (by direct suturing or grafting). Endoneural tubes disrupted so high chance of “miswiring” during regeneration.
Prognosis poor.

Question 6

What are closed nerve injuries associated with?

Answer 6

Associated with nerve injuries in continuity – neuropraxias, axonotmesis.

Question 7

Describe the outcome and surgical indication for closed nerve injuries

Answer 7

Spontaneous recovery possible.
Surgery indicated after 3 months if no recovery identified, monitored clinically + electromyography.
Axonal growth rate (1-3mm/day)

Question 8

What are examples of closed nerve injuries?

Answer 8

Typically stretching of nerve – brachial plexus injuries; radial nerve injury – humeral fracture.

Question 9

What are open nerve injuries associated with?

Answer 9

Frequently related to nerve division – neurotmetic injuries, e.g. knives/glass.

Question 10

Describe the treatment of open nerve injuries and result of the nerve after its injury

Answer 10

Treated with early surgery.

Distal portion of the nerve undergoes Wallerian degeneration – occurs up to 2 to 3 weeks after the injury.

Question 11

What is Wallerian degeneration?

Answer 11

Active process of degeneration that results when a nerve fibre is cut/crushed and the part of the axon distal to the injury degenerates.

Question 12

What are the different clinical features associated with nerve injury?

Answer 12

Sensory – dysaesthesiae (disordered sensation), anaesthesia, hypo and hyperaesthesia, paraesthesia
Motor – paresis (weakness) or paralysis +/- wasting, dry skin – sweat glands not stimulated
Reflexes – diminished or absent

Question 13

Describe the process of nerve healing

Answer 13

Very slow. Starts with initial death of axons distal to site of injury – Wallerian degeneration, then degradation of myelin sheath.
Proximal axon budding occurs after about 4 days.
Regeneration proceeds at rate of about 1mm/day, possibly 3-5mm/day in children. Pain is first modality to return.

Question 14

What does the prognosis for nerve recovery depend on?

Answer 14

Whether nerve is “pure” (only sensory or only motor) or “mixed” (both sensory and motor), how distal the lesion is (proximal lesions are worse).

Question 15

What can be used to monitor recovery?

Answer 15

Tinnel’s sign can monitor recovery (tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed).
Injury can be assessed, and recovery monitored by electrophysiological Nerve Conduction Studies.

Question 16

Describe use of direct nerve repair

Answer 16

For lacerations, no loss of nerve tissue. Using microscope/loupes, bundle repair, growth factors.

Question 17

Describe use of nerve grafting repair

Answer 17

For nerve loss. Late repair: retraction, sural nerve.

Question 18

Describe the rule of three with regards to surgery

Answer 18

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 after 3 months, for closed injuries.

Question 19

Illustrate the difference between UMN and LMN lesions with regards to: strength, tone, deep tendon reflexes, clonus, Babinski’s sign (toe fanning), atrophy.

Answer 19

UMN lesion: strength decreased, tone increased, reflexes increased, clonus present, Babinski’s sign present, atrophy absent
LMN lesion: strength decreased, tone decreased, reflexes decreased, clonus absent, Babinski’s sign absent, atropy present