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3rd Year - MSK Diseases > 1.3. Musculoskeletal Growth Injury and Repair - Peripheral Nerve Injuries > Flashcards

1.3. Musculoskeletal Growth Injury and Repair - Peripheral Nerve Injuries Flashcards

1
Q

What is a Motor Unit?

A

A Motor Axon, leaving from the Anterior Horn Cell (Gray Matter) of the Spinal Cord, to supply Muscle Fibres

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2
Q

What is a Sensory Unit?

A

Cell Bodies in the Posterior Root Ganglia (lie outside of the Spinal Cord)

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3
Q

What do Nerve Fibers join to form?

A
  1. Ventral (Anterior) Motor Roots

2. Dorsal (Posterior) Sensory Roots

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4
Q

What do the Ventral and Dorsal Nerve Roots combine to form?

A

A Spinal Nerve

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5
Q

Where do the Spinal Nerves exit the Vertebral Column?

A

Via an Intervertebral Foramen

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6
Q

What is a Peripheral Nerve?

A

A bundle of Nerve Fibres which are the part of the Spinal Nerve, Distal to the Nerve Roots

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7
Q

What is the size range for a Peripheral Nerve?

A

0.3-22 μm

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8
Q

What surrounds Peripheral Nerves?

A
  1. Schwann Cells form a thin Cytoplasmic Tube
  2. Myelin Sheath - Large Fibres are in a Multi-layered insulating Membrane
  3. Multiple layers of Connective Tissue surround the Axons
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9
Q

What are Axons?

A

Long processes of Neurons

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10
Q

What are Axons coated with?

A

Endoneurium

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11
Q

What are Axons grouped into?

A

Fascicles

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12
Q

What are Fascicles covered in?

A

Perineurium

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13
Q

What is formed when Fascicles are grouped?

A

A Nerve

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14
Q

What is a Nerve covered in?

A

Epineurium

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15
Q

What is a Neurone?

A

A Nerve Cell

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16
Q

What surrounds Neurons?

A

Schwann Cells

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17
Q

What are the different Nerve Fiber Categories? And what are their relative sizes?

A
  1. A-Alpha (Group 1A and 1B afferent’s) - 15 microns
  2. A-Beta (Group 2 afferent’s) - 12-14 microns
  3. A-Gamma - 8-10 microns
  4. A-Delta (Group 3 afferent’s) - 6-8 microns
  5. B - 2-5 microns
  6. C (Group 4 afferent’s) - <1 micron
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18
Q
  1. What is the function of A-Alpha Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. a) Large Motor Axons
  2. b) Muscle Stretch Sensory Axons
  3. c) Muscle Tension Sensory Axons
  4. 60-100m/s
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19
Q
  1. What is the function of A-Beta Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. a) Touch Sensory Axons
  2. b) Pressure Sensory Axons
  3. c) Vibration Sensory Axons
  4. d) Joint Position Sensory Axons
  5. 30-60m/s
20
Q
  1. What is the function of A-Gamma Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. Gamma Efferent Motor Axons

2. 15-30m/s

21
Q
  1. What is the function of A-Delta Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. a) Sharp Pain Sensation
  2. b) Very Light Touch Sensation
  3. c) Temperature Sensation
  4. 10-15m/s
22
Q
  1. What is the function of B Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. Sympathetic Pre-Ganglionic Motor Axons

2. 3-10m/s

23
Q
  1. What is the function of C Neurons?

2. What speed does nerve signal travel through them? (in meters / second)

A
  1. a) Dull, Aching Pain Sensation
  2. b) Burning Pain Sensation
  3. c) Temperature Sensation
  4. < 1.5m/s
24
Q

What are the 2 broad categories of injury which can occur to a nerve?

A
  1. Compression / Entrapment (at different possible levels)

2. Trauma

25
Q

What are some classical Compressive Nerve Injury Conditions?

A
  1. Carpal Tunnel Syndrome (Median Nerve at the Wrist)
  2. Sciatica (Spinal Root by the Intervertebral Disk)
  3. Morton’s Neuroma (Digital Nerve in 2nd / 3rd Web Space of Forefoot)
26
Q

What are the 2 Sub-Categories of Trauma Nerve Injury?

A
  1. Direct (Blow, Laceration)

2. Indirect (Avulsion, Traction)

27
Q

What are the 3 types of Trauma Nerve Injury?

Note - This is not the Direct vs Indirect question

A
  1. Neurapraxia
  2. Axonotmesis
  3. Neuromesis
28
Q

What is Neurapraxia?

A

Reversible conduction block of a Nerve caused by:
1. Stretching (8% will damage microcirculation)
2. Bruising
Leading to local Ischaemia and Demyelination

29
Q

What is the prognosis of Neurapraxia?

A

Good (Weeks to Months)

30
Q

Is Axonotmesis more severe than Neruapraxia?

A

Yes

31
Q

What is Axonotmesis?

A

Disruption of Axons, with the Endoneurium intact, caused by:

  1. Stretching ++ (15% elongation disrupts axons)
  2. Crushed Nerve
  3. Direct Blow to the Nerve
32
Q

What is the prognosis of Axonotmesis?

A
  1. Fair. Sensory recover better than motor, but often, not normal sensation returns but enough to recognize pain, hot/cold, sharp and blunt
  2. Wallerian degeneration follows
33
Q

Is Neurotmesis more severe than Axonotmesis?

A

Yes

34
Q

What is Neurotmesis?

A

Complete Nerve Division via either:

  1. Laceration
  2. Avulsion
35
Q

Is there any recovery from Neurotmesis?

A

Not unless it is repaired via suturing / grafting

36
Q

What is the prognosis of Meurotmesis?

A

Poor, Endoneural tubes are disrupted so there is a high chance of “Mis-wiring” during regeneration

37
Q

What is a Closed Nerve Injury associated with?

A

This is associated with Nerve Injuries in Continuity (Neuropraxia / Axonotmesis)

38
Q

How are Closed Nerve injuries treated?

A
  1. They aren’t, spontaneous recovery is possible (Axonal Growth rate is 1-3 mm/day)
  2. Surgery is indicated after 3 months
  3. If no recovery is identified then Electromyography is required
39
Q

What is an Open Nerve Injury associated with?

A 
Neurotmeic injuries (knives / glass)
Note - The distal portion of the nerve undergoes Wallerian Degeneration (occurs up to 2 weeks after the injury)
40
Q

How are Open Nerve Injuries treated?

A

Early Surgery

41
Q

What are the clinical features of Nerve Injury?

A

Sensory: Dysaethesiae (Disordered sensation)
Motor:
1. Paresis (Weakness) or Paralysis +/- Wasting
2. Dry Skin
Reflexes: Diminished / Absent

42
Q

How does the Nerve Heal after an Open Nerve Injury?

A
  1. Wallerian Degeneration (initial death of axons distal to the site of injury)
  2. Degradation of the Myelin Sheath
  3. Proximal Axonal Budding occurs (after 4 days)
  4. Regeneration proceeds at 1mm/day
    Note - Pain is the first modality to return
43
Q

What is the prognosis for recovery of an Open Nerve Injury dependent on?

A
  1. Whether the Nerve is:
  2. a) Pure - only sensory or motor
  3. b) Mixed - both sensory and motor
  4. How distal the lesion is (proximal is worse)
44
Q

How can:

  1. Injury be assessed?
  2. Recovery be monitored?
A
  1. Electrophyiological Nerve Conduction Studies
  2. a) Tinel’s Sign (tap along the nerve to see how distally they can feel)
  3. b) Electrophyiological Nerve Conduction Studies
45
Q

How can the Nerve be repaired?

A
  1. Direct Repair (For Laceration with no loss of nerve tissue)
  2. Nerve Grafting (Nerve loss)
46
Q

What is the “Rule of Three” when it comes to surgical timing in a traumatic peripheral nerve injury?

A
  1. Immediate Surgery within 3 days for Clean and Sharp Injuries
  2. Early Surgery within 3 weeks for Blunt/Contusion injuries
  3. Delayed Surgery, performed 3 months after injury, for closed injuries

3rd Year - MSK Diseases (43 decks)

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