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Systems: MSK AB > Peripheral Nerve Injuries > Flashcards

Peripheral Nerve Injuries Flashcards

1
Q

What is motor (efferent) composed of?

A
  • Anterior horn cell, (located in the gray matter of the spinal cord)
  • Motor axon,
  • Muscle fibres (neuromuscular junctions)
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2
Q

What is a sensory unit composed of?

A

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

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3
Q

What do nerve fibres join to form?

A
  • Anterior (ventral) motor roots

- Posterior (dorsal) sensory roots

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4
Q

How are spinal nerves formed?

A
  • Anterior and posterior roots combine to form a spinal nerve.
  • Exit the vertebral column via an intervertebral foramen.
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5
Q

What are peripheral nerves?

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

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

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6
Q

Describe the structure of peripheral nerves.

A
  • 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
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7
Q

How are peripheral nerves formed?

A

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

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8
Q

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

A
  • Large motor axons

- Muscle stretch and tension sensory axons

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9
Q

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

A

Touch, pressure, vibration and joint position sensory axons

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10
Q

What is the function of Ay fibres?

A

Gamma efferent motor fibres

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11
Q

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

A

Sharp pain, very light touch and temperature sensation

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12
Q

What is the function of B fibres?

A

Sympathetic preganglionic motor axons

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13
Q

What is the function of C fibres?

A

Dull, aching, burning pain and temperature sensation

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14
Q

What can compression at different levels result in?

A

Nerve palsies

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15
Q

How can a nerve be injured?

A
  • Compression

- Trauma (direct or indirect)

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16
Q

What types of trauma can occur to a nerve?

A
  • Neurapraxia
  • Axonotmesis
  • Neuromesis
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17
Q

What is neurapraxia?

A
  • Reversible conduction block (local ischaemia and demyelination)
  • Nerve is stretched or bruised
  • -Affects nerve in continuity
  • Prognosis is good
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18
Q

What is axonotmesis?

A
  • Rupture of axons within an intact endoneurium
  • Stretched or crushed or direct blow
  • Wallerian degeneration follows
  • Prognosis fair sensory>motor
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19
Q

Can peripheral nerves regenerate?

A

YES

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20
Q

What is neurotmesis?

A
  • 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
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21
Q

What grading system is used for peripheral nerve injury?

A

Sunderland grading

22
Q

What is the Sunderland grades?

A
  • 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
23
Q

What are closed injuries associated with?

A
  • Neuropraxis

- Axonotmesis

24
Q

What are the outcomes like for closed injuries?

A
  • Spontaneous recovery is possible
  • Surgery is indicated after 3 months
  • Axonal growth rate 1-3mm/day
25
Q

What are typical examples of closed injuries?

A

Typically stretching of a nerve

  • Brachial plexus injuries
  • Radial nerve humeral fracture
26
Q

What are open injuries frequently related to?

A

Neurotmetic injuries i.e. injured with knives or glass

27
Q

How are open injuries treated?

A

Early surgery

28
Q

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

A

Undergoes Wallerian degeneration

-Occurs up to 2-3 weeks after the injury

29
Q

What are the clinical features of nerve injury?

A

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

30
Q

How does peripheral nerve healing occur?

A
  • 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
31
Q

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

A

Pain

32
Q

What does the prognosis for recovery depend on?

A

Whether the nerve is

  • Pure
  • Mixed

How distal the lesion is
-Proximal is worse

33
Q

How can recovery from a nerve injury be monitored?

A
  • Tinel’s sign

- Electrophysiological nerve conduction studies

34
Q

What is Tinel’s sign?

A

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

35
Q

How is a direct nerve repair carried out?

A
  • Used for lacerations
  • No loss of nerve tissue
  • Microscope/loupes
  • Bundle repair
  • Growth factors administeered
36
Q

How is nerve grafting carried out?

A
  • Results in nerve loss

- Late repair

37
Q

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

A
  • 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.
38
Q

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

A

UMN vs LMN clinical signs

39
Q

UMN lesion: Strength

A

Decreased

40
Q

UMN lesion: Tone

A

Increased

41
Q

UMN lesion: Deep tendon reflexes

A

Increased

42
Q

UMN lesion: Clonus

A

Present

43
Q

UMN lesion: Babinski’s sign

A

Present

44
Q

UMN lesion: Atrophy

A

Absent

45
Q

LMN lesion: Strength

A

Decreased

46
Q

LMN lesion: Tone

A

Decreased

47
Q

LMN lesion: Deep tendon reflex

A

Decreased

48
Q

LMN lesion: Clonus

A

Absent

49
Q

LMN lesion: Babinski’s sign

A

Absent

50
Q

LMN lesion: Atrophy

A

Present

Systems: MSK AB (43 decks)

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