Musculoskeletal Growth/Injury and Repair - Nerve

Question 1

Peripheral Nerve Injuries are also known as what?

Answer 1

Lower Motor Neurone Injuries

Question 2

what makes up a peripheral nerve?

Answer 2

• Motor unit (efferent)
• Sensory unit
• Spinal Nerves

Question 3

what makes up the motor unit (efferent)

Answer 3

anterior horn cell, (located in the gray matter of the spinal cord)

motor axon,

muscle fibres (neuromuscular junctions)

Question 4

what makes up the sensory unit?

Answer 4

cell bodies in posterior root ganglia

I.e. lie outside the spinal cord

Question 5

nerve fibres join to form what?

Answer 5

anterior (ventral) motor roots

posterior (dorsal) sensory roots

Question 6

what makes up spinal nerves?

Answer 6

Anterior and posterior roots combine to form a spinal nerve

Exit the vertebral column via an intervertebral foramen

Question 7

what are the featuresof a peripheral nerve?

Answer 7

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

Question 8

Structure:

• peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue

• AXONS (long processes of neurones) are coated with __________ and grouped into
• FASCICLES (nerve bundles ) covered with __________; these are grouped to form the
• NERVE which is covered with __________

Answer 8

endoneurium

perineurium

epineurium

Question 9

anatomy - structure:

• neurone (nerve cell), surrounded by _________ cell
• bundles

Answer 9

Schwann

Question 10

what are the different Fiber types and functions (from largest to smallest)?

Answer 10

Increasing size = increasing speed of transmission

Question 11

what are the different types of injury that can occur to a nerve?

Answer 11

• compression (at different possible levels) [refer: lecture “Nerve palsies in the limbs”]
• trauma - direct (blow, laceration) or indirect (avulsion, traction)
• neurapraxia
• axonotmesis
• neurotmesis

Question 12

compression - entrapment

what are some classical conditions seen?

Answer 12

Carpal tunnel syndrome - Median nerve at wrist

Sciatica - Spinal root by intervertebral disc

Morton’s neuroma - (digital nerve in 2nd or 3rd web space of forefoot)

Question 13

what are the 3 different types of trauma?

Answer 13

neurapraxia

axonotmesis

neurotmesis

Question 14

what is neurapraxia?

Answer 14

nerve in continuity

stretched (8% will damage microcirculation) or bruised

reversible conduction block - local ischaemia and demyelination

prognosis good (weeks or months)

Neurapraxia is a disorder of the peripheral nervous system in which there is a temporary loss of motor and sensory function due to blockage of nerve conduction, usually lasting an average of six to eight weeks before full recovery

Question 15

what is axonotmesis?

Answer 15

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)

The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact

Question 16

can peripheral nerves regenerate?

Answer 16

yes

Question 17

what is neurotmesis?

Answer 17

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

most serious nerve injury in the scheme. In this type of injury, both the nerve and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is impossible

Question 18

summary picture showing the different types of truma

Answer 18

Neurapraxia – axon in tact but just one area not working

Axonotmesis – axon has disappeared and will have to grow down endoneurial tube

Neurotmesis – different severities, so may just have endoneurium disrupted, perineurial destruction and epineural destruction and indicate different prognosis’s

Question 19

what is a clsoed nerve injury?

Answer 19

• Associated with nerve injuries in continuity - neuropraxis and axonotmesis
• spontaneous recovery is possible
• surgery indicated after 3 months - if no recovery is identified, Clinical or Electromyography
• axonal growth rate (1–3 mm/day)
• Examples - Typically stretching of nerve, brachial plexus injuries or Radial Nerve humeral fracture

Question 20

what is an open nerve injury?

Answer 20

• Frequently related to nerve division, neurotmetic injuries E.g. knives/glass
• Treated with early surgery
• Distal portion of the nerve undergoes Wallerian degeneration - Occurs up 2 to 3 weeks after the injury

(wallerian degeneration - active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron’s cell body) degenerates)

Question 21

Injury - clinical features

what are some sensory features?

Answer 21

dysaethesiae (disordered sensation)

anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)

Question 22

Injury - clinical features

what are some motor features?

Answer 22

paresis (weakness) or paralysis ± wasting

dry skin - loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin

Question 23

Injury - clinical features

what are some reflex features?

Answer 23

diminished or absent

Question 24

what is the process of nerves healing?

Answer 24

• 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

Question 25

helaing - regeneration proceeds at rate of about what?

Answer 25

regeneration proceeds at rate of about 1 mm/day (or 1 inch/month) - poss. 3-5 mm/day in children

Question 26

what is the first modality to return in healing nerves?

Answer 26

pain

Question 27

prognosis for recoverey depends on what?

Answer 27

•whether nerve is –“pure” (only sensory or only motor) –“mixed” (both sensory and motor within same nerve) •how distal the lesion is (proximal worse) Mixed nerve have a varied recovers as the nerves can recover down the wrong tubes If it is a long way back to grow end plate may not still be functioning

Question 28

how can injury and recovery be monitored?

Answer 28

* Tinel’s sign can monitor recovery - (tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed) * Injury can be assessed, and recovery monitored - by electrophysiological Nerve Conduction Studies

Question 29

how is nerve repair done?

Answer 29

• Direct Repair - Laceration - 2 ends clsoe together - No loss nerve tissue - Microscope/Loupes - Bundle repair - Growth factors • Nerve Grafting (when ends cant be pulled together) - Nerve loss - Late repair - (retraction), Sural nerve

Question 30

THE “RULE OF THREE” Surgical timing in a traumatic peripheral nerve injury what is it?

Answer 30

* 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 31

Peripheral or Central nerve injury? how do you tell?

Answer 31

* Peripheral nerve injuries may result in loss of motor function, sensory function, or both * Injuries to the central nervous system may cause loss of motor function, sensory function, or both * How do I tell the difference clinically? Where there is no or limited muscle stimulation the muscle will atrophy so in UMN there is increased in tone and activity atrophy is absent