Nerve Injury

Question 1

Motor Unit

Answer 1

This is the anterior horn cell, the motor axon and the muscle fibres

Question 2

Sensory Unit

Answer 2

The cell bodies are in the posterior dorsal root ganglian

Question 3

Nerve fibres join to form

Answer 3

Anterior motor roots or posterior sensory roots.

Question 4

Spinal nerves

Answer 4

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

Question 5

Peripheral Nerve

Answer 5

This is the part of the spinal nerve distal to the nerve roots.

Question 6

Diameter of bundles of peripheral nerves

Answer 6

0.3-22 micrometers.

Question 7

Structure of the peripheral nerve

Answer 7

The peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue. The Axons are coated with endoneurium and grouped into fascicles which are covered with perineurium and these are grouped together to form the nerve which is covered with epineurium.

Question 8

Aa Fibres

Answer 8

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

Question 9

Ab fibres

Answer 9

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

Question 10

Ag fibres

Answer 10

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

Question 11

Ad Fibres

Answer 11

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

Question 12

B fibres

Answer 12

2-5 microns, 3-10m/s sympathetic preganglionic motor fibres

Question 13

C fibres

Answer 13

<1 micron, <1.5m/s, dull, aching and burning pain, temperature sensation

Question 14

Different injury types

Answer 14

Compression, trauma, indirect due to avulsion or traction

Question 15

Compression

Answer 15

Usually results due to entrapment. Carpal tunnel, sciatica and Mortons Neuroma

Question 16

Carpal Tunnel Syndrome

Answer 16

This is when the median nerve is compressed at the wrist

Question 17

Sciatica

Answer 17

This is when the spinal root is compressed by the intervertebral disc

Question 18

Mortons Neuroma

Answer 18

Compression of the ditial nerve in the 2nd or 3rd webspace of the foot

Question 19

Neurapraxia

Answer 19

When the nerve is stretched or bruised. This results in reversible conduction block due to local ischaemia and demyelination.

Question 20

Axonotmesis

Answer 20

The endoneurium is intact, but disruption to the axon occurs. Results from massive stretch(15%), compression or direct blow. Wallerian degeneration follows. The prognosis is fair and sensory recovery is often better than motor.

Question 21

Neurotmesis

Answer 21

Complete nerve division due to laceration or avulsion. There is no recovery at all unless the injury is successfully repaired. The endoneural tubes are disrupted so theres a high chance of “miswiring” during regeneration.

Question 22

Closed nerve injury

Answer 22

This is associated with nerve injuries in continuity. Spontaneous recovery is possible but surgery is indicated after three months if no recovery is indicated by clinical or electromyography review. Axonal growth rate is 1-3mm/day. Common examples of closed nerve injury are brachial plexus injuries and radial nerve humeral fracture.

Question 23

Open Nerve Injury

Answer 23

this is frequently related to nerve division (for example neurotmetic injuries with knives or glasses). This has to be treated early with surgery is repair is expected. The distal portion of the nerve undergoes Wallerian degeneration (occurs up 2 to 3 weeks after injury).

Question 24

Sensory clinical features of nerve injury

Answer 24

dysaethesia (disordered sensation). This can be anaesthetic (numb), hypo and hyperaethetic, paraesthetic (pins and needles).

Question 25

Motor clinical features of nerve injury

Answer 25

paresis or paralysis and muscle wasting. Dry skin can also occur (due to loss of tactile adherence since sudomotor nerve dibres not stimulating sweat glands in skin).

Question 26

Reflexes in nerve injury

Answer 26

Diminished or absent

Question 27

Nerve healing

Answer 27

This is very very slow. It stars with initial death of axons distal to the site of the injury (wallerian degeneration, then degeneration of the myelin sheath). The proximal axonal budding occurs after about 4 days.

Question 28

First modality to return

Answer 28

Pain sensation.

Question 29

Worse prognosis

Answer 29

The more proximal the injury

Question 30

Tinels sign

Answer 30

Used to monitor recovery. Tap over the site of the nerve and paraesthesia will be felt as far distally as regeneration has progressed.

Question 31

Rate of regeneration

Answer 31

1mm/day however this is slightly quicker in children (3-5mm/day).

Question 32

Direct nerve repair

Answer 32

• Laceration
• No loss nerve tissue
• Microscope/Loupes
• Bundle repair
• Growth factors

Question 33

Nerve grafting

Answer 33

• Nerve loss

* Late repair – retraction, sural nerve

Question 34

Surgical timing in traumatic peripheral nerve injury

Answer 34

• immediate surgery within three days for clean and sharp injuries
• Early surgery within three weeks for blunt/contusion injuries
• Delayed surgery, performed three months after injury for closed injuries