Peripheral Nerve Injuries Flashcards
What is a motor unit?
Anterior horn cell, motor axon and muscle fibres
What are spinal nerves?
Anterior and posterior roots combine to form a spinal nerve
Exit vertebral column via intervertebral foramen
Describe a peripheral nerve
Range in size - 0.3-22um
Schwann cells form thin tube around
Larger fibres in a multi-layered insulated membrane (myelin sheath)
Multiple layers of CT surrounding axons
Describe the structure of a peripheral nerve
Highly organised structure comprised of nerve fibres, blood vessels, and CT
Axons are coated in endoneurium
Fascicles covered in perineurium
Nerve covered on epineurium
What increases when size of fibre increases?
Speed of transmission
Describe A-alpha fibres
Size - 15 microns
Speed - 60-100 m/sec
Large motor axons - muscle stretch and tension sensory axons
Describe A-beta fibres
Size - 12-14 microns
Speed - 30-60m/sec
Touch, pressure, vibration, and joint position - sensory axons
Describe A-gamma fibres
Size - 8-10 microns
Speed - 15-30 m/sec
Gamma efferent motor axons
Describe A-delta fibres
Size - 6-8 microns
Speed - 10-15m/sec
Sharp pain, very light touch and temp. sensation
Describe B fibres
Size - 2-5 microns
Speed - 3-10m/sec
Sympathetic preganglionic motor axons
Describe C fibres
Size - <1 microns
Speed - <1.5m/sec
Dull, aching, burning pain and temp. sensation
What are the causes of nerve injury?
Compression
Trauma - direct and indirect
Neuropraxia
Axonotmesis
Neurotmesis
What are classical conditions from compression of nerve?
Carpel tunnel syndrome - median nerve at wrist
Sciatica - spinal root by intravertebral disc
Morton’s neuroma - 2nd and 3rd space of forefoot digital nerve
Describe neurapraxia
Nerve in continuity
Stretched or bruised
Reversible conduction block from local ischaemia and demyelination
Prognosis good
Describe axonotmesis
Endoneurium intact but disruption of axons - more severe
Stretched, direct blow or crushed
Wallerian degeneration follows
Prognosis fair - sensory often better than motor
Can peripheral nerves regenerate?
Yes
Describe neurotmesis
Complete nerve division
Laceration or avulsion
No recovery unless repaired (suturing or grafting)
Prognosis poor
As endoneural tubes disrupted then high chance of miswiring
What are closed nerve injuries associated with?
Nerve injuries in continuity - neuropraxias and axonotmesis (whole nerve still intact)
Describe closed nerve injury
Spontaneous recovery is possible
Surgery indicated after 3 months - if no recovery then clinical and EMG
Axonal growth rate is 1-3mm/day
What are examples of cloased nerve injury?
Brachial plexus injury
Radial nerve humeral fracture
What is open nerve injury related to?
Nerve division - neurotmesis injury - ex. knives and glass
Describe open nerve injury
Treated with early surgery
Distal portion of nerve undergoes Wallerian degeneration - occurs 2-3 weeks after injury
What are the clinical features of nerve injury?
Sensory - dysesthesia (disordered sensation) includes anaesthetic and paraesthetic
Motor - paresis or paralysis/ wasting , and dry skin (fibres not stimulating sweat glands)
Reflexes - diminished or absent
Describe nerve healing
Very slow
Starts with initial death of axons distal to site of injury - Wallerian degeneration then myelin sheath degeneration
Proximal axonal budding starts after 4 days
What is the regeneration rate of a nerve?
1mm/ day
Pain is fist modality to return
What does the prognosis for recovery depend on?
Pure or mixed nerve
Pure is better prognosis as always grow down to nerve plate even if not correct one
Mixed are variable (sensory and motor can grow down wrong tube)
More proximal then worse
What is Tinel’s sign?
Tap over site of nerve and paraesthesia will be felt as far as distally as regeneration has progressed - used to monitor recovery
How can injury be assessed and recovery monitored?
Electrophysiological nerve conduction studies
When is direct nerve repair done?
Laceration and no loss of nerve tissue
Is under microscope
Is a bundle repair - helps dock tubes to match with end plates
When is nerve grafting used?
Nerve loss and late repair
Use sural nerve - creates a passage for axons to grow down
What are the findings of UMN lesions?
Strength decreased, tone increased, deep tendon reflexes increased, clonus present, Babinski’s sign is present and atrophy absent
What are some findings of LMN lesion?
Decreased strength, decreased tone, decreased reflexes, absent clonus and Babinski’s sign, and atrophy is present
