MSK growth injury and repair - Peripheral Nerve injuries (LMN injuries)

Question 1

Define a peripheral nerve

Answer 1

part of the spinal nerve distal to the nerve roots.

Question 2

what are axons covered by and grouped into?

Answer 2

Endoneurium - Fascicles

Question 3

what are Fascicles covered by and grouped into?

Answer 3

Perineurium - Nerve

Question 4

what are nerves covered by?

Answer 4

Epineurium

Question 5

what are nerve cells surrounded by?

Answer 5

Schwann cells

Question 6

Size and function of fibre - Aalpha

Answer 6

15microns, Large motor axons, muscle, stretch and tension sensory axons

Question 7

Size and function of fibre - Abeta

Answer 7

12-14microns, touch, pressure, vibration and proprioception

Question 8

Size and function of fibre - Agamma

Answer 8

8-10microns, gamma efferent motor axons

Question 9

Size and function of fibre - Adelta

Answer 9

6-8microns, sharp pain, very light touch and temperature sensation

Question 10

Size and function of fibre - B

Answer 10

2-5microns, sympathetic preganglion motor axons

Question 11

Size and function of fibre - C

Answer 11

<1micron, dull, aching, burning pain and temperature sensation

Question 12

what are the classical nerve compression conditions?

Answer 12

carpal tunnel syndrome (median n. at the wrist), sciatica (spinal root by ivdisc), mortons neuroma (digital n. in 2nd/3rd web space or forefoot)

Question 13

what is Neurapraxia?

Answer 13

the nerve is in continuity, stretched or bruised, reversible conduction block - local ischaemia and demyelination

Question 14

what is Axonotmesis?

Answer 14

endoneurium intact (tube in continuity), but disruption of axons; more severe injury, stretched ++ (15% elongation disrupts axons) or crushed or direct blow, Wallerian degeneration follows, prognosis fair (sensory recovery often better than motor - often not normal but enough to recognise pain, hot & cold, sharp & blunt)

Question 15

what is Neurotmesis?

Answer 15

Complete nerve division, laceration or avulsion, no recovery unless repaired (by grafting or suturing), endoneural tubes disrupted so high chance of “miswiring” during regeneration, prognosis poor

Question 16

give examples of closed nerve injuries

Answer 16

brachial plexus injury/stretching, radial nerve humeral fracture

Question 17

give examples of open nerve injuries

Answer 17

neurotmatic, knives and glass, the distal portion of the nerve undergoes wallerian degeneration

Question 18

clinical features of nerve injury - sensory, motor, reflexes?

Answer 18

sensory - dysaethesiae (disordered sensation), motor - paresis (weakness) or paralysis and wasting, dry skin, loss of tactile adherance since sudomotor (sweat) nerve fibres not stimulating sweat glands in the skin. Reflexes - diminished or absent.

Question 19

how does healing take place?

Answer 19

very slow!! starts with initial death of axons distal to site of injury, Wallerian degeneration, Then degradation myelin sheath, proximal axonal budding occurs after about 4 days, regeneration proceeds at rate of about 1 mm/day, pain is the first modality to return

Question 20

what is tinels sign and what is it used for?

Answer 20

tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed - used to monitor recovery and for the clinical assessment of Carpal Tunnel syndrome

Question 21

how else can injury be assessed and recovery monitored?

ix of nerves

Answer 21

electrophysiological nerve conduction studies NCS OR EMG (Electromyography)

Question 22

what is the rule of 3 in surgical timing in a traumatic peropheral nerve injury?

Answer 22

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 23

UMN LESION

Answer 23

decreased strength, increased tone, reflexes, clonus present, babinskis present, atrophy present

Question 24

LMN LESION

Answer 24

decreased strength, decreased tone, reflexes.