Peripheral Nerve Injuries

Question 1

What is motor (efferent) composed of?

Answer 1

• Anterior horn cell, (located in the gray matter of the spinal cord)
• Motor axon,
• Muscle fibres (neuromuscular junctions)

Question 2

What is a sensory unit composed of?

Answer 2

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

Question 3

What do nerve fibres join to form?

Answer 3

• Anterior (ventral) motor roots

- Posterior (dorsal) sensory roots

Question 4

How are spinal nerves formed?

Answer 4

• Anterior and posterior roots combine to form a spinal nerve.
• Exit the vertebral column via an intervertebral foramen.

Question 5

What are peripheral nerves?

Answer 5

• The part of a spinal nerve distal to the nerve roots

- A highly organised structure comprised of nerve fibres, blood vessels and connective tissue

Question 6

Describe the structure of peripheral nerves.

Answer 6

• 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 7

How are peripheral nerves formed?

Answer 7

AXONS (long processes of neurones) are coated with endoneurium and grouped into FASCICLES (nerve bundles ) covered with perineurium; these are grouped to form the NERVE which is covered with epineurium

Question 8

What is the function of Aa (group IA and IB afferents) fibres?

Answer 8

• Large motor axons

- Muscle stretch and tension sensory axons

Question 9

What is the function of AB (group II afferents) fibres?

Answer 9

Touch, pressure, vibration and joint position sensory axons

Question 10

What is the function of Ay fibres?

Answer 10

Gamma efferent motor fibres

Question 11

What is the function of Ad (group III afferent) fibres?

Answer 11

Sharp pain, very light touch and temperature sensation

Question 12

What is the function of B fibres?

Answer 12

Sympathetic preganglionic motor axons

Question 13

What is the function of C fibres?

Answer 13

Dull, aching, burning pain and temperature sensation

Question 14

What can compression at different levels result in?

Answer 14

Nerve palsies

Question 15

How can a nerve be injured?

Answer 15

• Compression

- Trauma (direct or indirect)

Question 16

What types of trauma can occur to a nerve?

Answer 16

• Neurapraxia
• Axonotmesis
• Neuromesis

Question 17

What is neurapraxia?

Answer 17

• Reversible conduction block (local ischaemia and demyelination)
• Nerve is stretched or bruised
• -Affects nerve in continuity
• Prognosis is good

Question 18

What is axonotmesis?

Answer 18

• Rupture of axons within an intact endoneurium
• Stretched or crushed or direct blow
• Wallerian degeneration follows
• Prognosis fair sensory>motor

Question 19

Can peripheral nerves regenerate?

Answer 19

YES

Question 20

What is neurotmesis?

Answer 20

• Complete severance of a peripheral nerve by laceration or avulsion
• No recovery unless repaired (direct suturing or graft)
• Endoneural tubes disrupted so high chance of miswiring during regeneration
• Prognosis is poor

Question 21

What grading system is used for peripheral nerve injury?

Answer 21

Sunderland grading

Question 22

What is the Sunderland grades?

Answer 22

• Grade 1 Neuropraxia
• Grade 2 Axonotmesis
• Grade 3 Neurotmesis with intact perinerium
• Grade 4: Neurotmesis with intact epineurium
• Grade 5: Neurotemesis with complete severance of all layers

Question 23

What are closed injuries associated with?

Answer 23

• Neuropraxis

- Axonotmesis

Question 24

What are the outcomes like for closed injuries?

Answer 24

• Spontaneous recovery is possible
• Surgery is indicated after 3 months
• Axonal growth rate 1-3mm/day

Question 25

What are typical examples of closed injuries?

Answer 25

Typically stretching of a nerve - Brachial plexus injuries - Radial nerve humeral fracture

Question 26

What are open injuries frequently related to?

Answer 26

Neurotmetic injuries i.e. injured with knives or glass

Question 27

How are open injuries treated?

Answer 27

Early surgery

Question 28

What happens to the distal portion of the nerve in open injuries?

Answer 28

Undergoes Wallerian degeneration | -Occurs up to 2-3 weeks after the injury

Question 29

What are the clinical features of nerve injury?

Answer 29

Sensory -Dysesthesia (anaesthesia, hypo and hyper aesthetic, paraesthesia) Motor - Paresis or paralysis and wasting - Dry skin (loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin) Reflexes -Diminished or absent

Question 30

How does peripheral nerve healing occur?

Answer 30

- Very slow process - Starts with initial death of axons distal to site of injury (Wallerian degeneration) then degradation of the myelin sheath - Proximal axonal budding occurs after about 4 days - Regeneration proceeds at rate of about 1mm/day

Question 31

What is the first modality to return as a nerve heals?

Answer 31

Pain

Question 32

What does the prognosis for recovery depend on?

Answer 32

Whether the nerve is - Pure - Mixed How distal the lesion is -Proximal is worse

Question 33

How can recovery from a nerve injury be monitored?

Answer 33

- Tinel's sign | - Electrophysiological nerve conduction studies

Question 34

What is Tinel's sign?

Answer 34

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

Question 35

How is a direct nerve repair carried out?

Answer 35

- Used for lacerations - No loss of nerve tissue - Microscope/loupes - Bundle repair - Growth factors administeered

Question 36

How is nerve grafting carried out?

Answer 36

- Results in nerve loss | - Late repair

Question 37

What is the rule of 3 in the surgical timing in a traumatic peripheral nerve injury?

Answer 37

- 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 38

How to tell the difference between peripheral and central nerve injuries clinically?

Answer 38

UMN vs LMN clinical signs

Question 39

UMN lesion: Strength

Answer 39

Decreased

Question 40

UMN lesion: Tone

Answer 40

Increased

Question 41

UMN lesion: Deep tendon reflexes

Answer 41

Increased

Question 42

UMN lesion: Clonus

Answer 42

Present

Question 43

UMN lesion: Babinski's sign

Answer 43

Present

Question 44

UMN lesion: Atrophy

Answer 44

Absent

Question 45

LMN lesion: Strength

Answer 45

Decreased

Question 46

LMN lesion: Tone

Answer 46

Decreased

Question 47

LMN lesion: Deep tendon reflex

Answer 47

Decreased

Question 48

LMN lesion: Clonus

Answer 48

Absent

Question 49

LMN lesion: Babinski's sign

Answer 49

Absent

Question 50

LMN lesion: Atrophy

Answer 50

Present