Peripheral nerve injuries

Question 1

Define the motor unit (efferent) of a nerve

Answer 1

• Anterior horn cell (in gray matter of spinal cord)
• Motor axon
• Muscle fibres (NMJs)

Question 2

Define sensory unit of a nerve

Answer 2

-Cell bodies in posterior root ganglia (lie outside spinal cord)

Question 3

What do nerve fibres join to form?

Answer 3

• Anterior (ventral) motor roots

- Posterior (dorsal) sensory roots

Question 4

Where do spinal nerves exit (formed by anterior and posterior roots combining)

Answer 4

Vertebral column via intervertebral foramen

Question 5

What is the peripheral nerve?

Answer 5

• Part of spinal nerve distal to nerve roots
• Bundles of nerve fibres
• Diameter 0.3-22 micrometres
• Schwann cells form thin cytoplasmic tube around
• Larger fibres in multi layered insulating membrane (myelin sheath

Question 6

Discuss the structure of peripheral nerves

Answer 6

• Axons coated with endoneurium, are grouped into
• Fascicles (bundles) covered with perineurium, are grouped to form
• Nerve, which is covered with epineurium

Question 7

What different types of injuries to nerves can occur?

Answer 7

• Compression

- Trauma (direct/indirect)

Question 8

What sort of examples are of compression of nerves?

Answer 8

• Carpal tunnel syndrome
• Sciatica
• Mortons neuroma

Question 9

What examples of direct trauma to nerves are there?

Answer 9

• Blow

- Laceration

Question 10

What examples of indirect trauma are there?

Answer 10

• Avulsion

- Traction

Question 11

What is neurapraxia?

Answer 11

• Stretched or bruised, local ischaemia and demyelination (reversible conduction block)
• Nerve in continuity
• Prognosis good (wks/mths)

Question 12

What is axonotmesis?

Answer 12

• Stretched/crushed/direct blow to nerve
• Endoneurium intact but axons disrupted (tube in continuity). More severe injury
• Wallerian degeneration follows
• Prognosis fair (sensory recovery often better than motor)

Question 13

What is neurotmesis?

Answer 13

• Complete nerve division
• Laceration/avulsion
• No recovery unless repaired
• Prognosis poor

Question 14

What grading is used to determine extent of nerve injury?

Answer 14

Sutherland grade (grade 5 worst)

Question 15

Discuss closed nerve injuries and give examples

Answer 15

• Associated with nerve injuries in continuity (neuropraxis, axonotmesis)
• Spontaneous recovery possibly, surgery indicated after 3m (do EMG if no recovery)

Examples

• Brachial plexus injuries
• Radial nerve humerus fracture

Question 16

Discuss open nerve injuries and give examples

Answer 16

• Related to nerve divsion (neurotmesis)
• Early surgery
• Eg knives/glass

Question 17

Clinical features of nerve injury?

Answer 17

-Sensory
>Dysaethesiae

-Motor
>Paresis/paralysis
>Dry skin

-Reflexes
>Reduced/absent

Question 18

Discuss healing of nerve injuries

Answer 18

• Slow
• Starts with initial axon death distal to injury (wallerian degeneration then degradation of myelin sheath)
• Proximal axon budding after 4d

Question 19

What is the regeneration rate?

Answer 19

1mm/day. Pain modality first to return

Question 20

What is tinels sign (can monitor recovery)

Answer 20

Tapping over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed

Nerve conduction studies can also monitor recovery

Question 21

What two ways can surgery be used to repair nerves?

Answer 21

• Direct repair

- Nerve graft

Question 22

What is rule of 3 for surgical timing in peripheral nerve injury?

Answer 22

• Immediate surgery within 3d for clean/sharp injuries
• Early surgery within 3w for blunt/contusion injuries
• Delayed surgery after 3m for closed injuries