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Musculoskeletal System > Peripheral Nerve Injuries > Flashcards

Peripheral Nerve Injuries Flashcards

1
Q

What does a Motor unit consist of?

A

Anterior horn cell (located in grey mater)
Motor axon
Muscle fibres (neuromuscular junctions).

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2
Q

What does a sensory unit consist of?

A

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

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3
Q

What is a spinal nerve?

A

Combination of Anterior and posterior roots. They exit the vertebral column via intervertebral foramen.

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4
Q

What are some characteristics of Peripheral nerves?

A

They are part of the spinal nerve distal to the nerve roots.
Bundles of nerve fibres.
Range in diameter from 0.3-22um.
Schwann cells form a thin cytoplasmic tube around them.
Larger fibres in a multilayered insulating membrane (myelin sheath).
Multiple layers of connective tissue surrounding their axons.

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5
Q

What is the structure of a peripheral nerve?

A

Axons are coated with endoneurium and grouped into fascicles (nerve bundles) covered with perineurium. These are grouped to form the nerve which is covered in epineurium.

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6
Q

What is the size, speed and function of A alpha fibres (group IA and IB afferents)?

A

15 microns
60-100 m/s
Large motor axons
Muscle stretch and tension sensory axons.

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7
Q

What is the size, speed and function of A beta fibres (group II afferents)?

A

12-14 microns
30-60m/s
Touch, pressure, vibration and joint position sensory axons.

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8
Q

What is the size, speed and function of A gamma fibres?

A

8-10 microns
15-30 m/s
Gamma efferent motor axons

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9
Q

What is the size, speed and function of A delta fibres (group III afferents)?

A

6-8 microns
10-15 m/s
Sharp pain, very light touch and temperature sensation.

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10
Q

What is the size, speed and function of B fibres?

A

2-5 microns
3-10 m/s
Sympathetic preganglionic motor axons.

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11
Q

What is the size, speed and function of C fibres (group IV afferents)?

A

<1 microns
<1.5 m/s
Dull, aching, burning pain and temperature sensation.

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12
Q

What is neuropraxia?

A

A transient conduction block of motor or sensory function without nerve degeneration, although loss of motor function is the most common finding.
Mildest form of peripheral nerve injury.

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13
Q

What is axonotmesis?

A

Injury to the peripheral nerve of one extremity of the body.
The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact.

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14
Q

What is neurotmesis?

A

Most serious nerve injury.
Both the nerve and nerve sheath are damaged.
Results in complete paralysis due to complete division of the nerve.

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15
Q

What is Morton’s neuroma?

A

Painful condition that affects the ball of your foot. Compression of digital nerve in 2nd and 3rd web space of foot.

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16
Q

What are some characteristics of Axonotmesis?

A

Endoneurium intact
Stretched, crushed or direct blow causes it.
Wallerian degeneration follows - active process of degernation after a nerve has been cut.
Prognosis is fair - sensory recovery is often better than motor. It doesn’t return to normal but enough to recognise pain, hot and cold, sharp and blunt.

17
Q

What are some characteristics of Neurotmesis?

A

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.

18
Q

How are peripheral nerve injuries classified?

A

Sunderland Grade Scheme:

Sunderland grade 1 = neuropraxia

Sunderland grade 2 = Axonotmesis

Sunderland grade 3 = Neurotmesis

Sunderland grade 4 = Neurotmesis +

Sunderland grade 5 = Neurotmesis ++

19
Q

What is meant by a closed nerve injury?

A

Associated with nerve injuries in continuity e.g neuropraxis, axonotmesis.
Spontaneous recovery is possible
Surgery indicated after 3 months if no recovery is identified - clinical/electromyography.
Axonal growth rate (1-3mm/per day).
Typically stretching of nerve e.g brachial plexus injuries, radial nerve humeral fracture.

20
Q

What is meant by an open nerve injury?

A

Frequently related to nerve division e.g neurotmetic injuries (knives, glass etc).
Treated with early surgery.
Distal portion of the nerve undergoes Wallerian degeneration, occurring 2-3weeks after the injury.

21
Q

What is dysaethesiae?

A

Disordered sensation

22
Q

What are some clinical features of sensory nerve injuries?

A

Dysaethesiae
Anaesthetic
Hypo & hyper aesthetic
Paraesthetic (pins and needles).

23
Q

What are some clinical features of motor nerve injuries?

A

Paresis (weakness)
Paralysis
Wasting
Dry skin - loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin.

24
Q

What are some characteristics of healing after nerve injuries?

A

Very slow
Starts with initial death of axons distal to site of injury - Wallerian degeneration followed by degradation of myelin sheath.
Proximal axonal budding occurs after about 4 days.
Regeneration proceeds at a rate of 1mm/day (more in kids).
Pain is first mobility to return.
Prognosis depends if nerve is pure = only sensory or only motor, or mixed = both within the same nerve. It also depends on how distal the lesion is (proximal is worse).

25
Q

How is recovery after a nerve injury monitored?

A

Tinel’s sign - tap over site of nerve and paraesthesia will be felt as far distally as regeneration had progressed.

Electrophysiological nerve conduction studies.

26
Q

What are some examples of direct nerve repair?

A 
Laceration
No loss nerve tissue
Microscope/loupes
Bundle repair
Growth factors
27
Q

What is the rule of 3 relating to 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.

28
Q

What are the findings of an upper motor neurone lesion?

A 
Decreased strength
Increased tone
Increased deep tendon reflexes
Clonus present
Babinski's sign present
Atrophy absent.
29
Q

What are the findings of a lower motor neurone lesion?

A 
Decreased strength
Decreased tone
Decreased deep tendon reflexes
Clonus absent
Babinski's sign absent
Atrophy present

Musculoskeletal System (20 decks)

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