Nerve Growth & Repair Flashcards
What are the layers of a peripheral nerve?
Axons covered in endoneurium
Fascicles covered in perineurium
Nerves covered in epineurium
All covered in a myelin sheath by schwann cells
Which are the fastest nerves?
Aalpha
Large motor axons + muscle stretch/tension sensory axons
What are the 2nd fastest nerves?
Abeta
Carry innocuous sensation e.g. touch, pressure, vibration and proprioception
What are the 3rd and 4th fastest nerves?
Agamma - Gamma Efferent motor neurons
Adelta - Carry sharp pain & heat
What do B fibres carry?
Sympathetic motor axons (2nd slowest type)
What do C fibres carry?
Dull/ache pain
burning pain
Cold
What are the types of nerve injury?
Compression
Trauma:
- Direct e.g. blow or laceration
- Indirect e.g. Avulsion or traction
These result in:
- Neurapraxia
- Axonetmesis
- Neurotmesis
What type of nerve injury are carpal tunnel, sciatica & Morton’s neuroma?
Compression injuries
Define Neurapraxia?
Nerve is unbroken but stretched or bruised
Local ischaemia –> reversible conduction block
Define Axonetmesis?
Endoneurium still intact but axons are damaged resulting in Wallerian degeneration
Recovery is rarely full but sensory is better than motor
Define Neurotmesis?
Complete nerve division due to avulsion or laceration
Requires suturing/grafting for any recovery and prognosis is poor
A closed nerve injury is neuropraxis or axonotmesis where the nerve sheath is intact. How do we handle them?
Spontaneous recovery is possible
Do surgery if no recovery is identified by EMG or clinically after 3 months
What type of nerve injury are common with brachial plexus injuries and humeral fractures?
Closed
An open nerve injury is usually a knife or glass that divides the nerve –> Neurotmesis. How do we handle them?
Early surgery
What are the consequences of a nerve injury? (I.e. the symptoms/signs)
Dysaesthesia
Paresis, paralysis +/- wasting
Dry Skin
Loss of reflexes
Wallerian degeneration is when the distal axon dies following injury, how long does it take for proximal axonal budding to occur?
~4 days
How fast do nerves regrow?
1mm/day (1inch/month)
Pain is the first modality to return
How might you monitor a nerve’s regrowth?
- Tinnel’s Sign
- Nerve Conduction studies
When would we do direct nerve repair vs nerve grafting?
Direct repair if the tissues still there and we get in early. Can use growth factors as well
Grafting if the nerve is lost or late repair. often use sural nerve
When referring to the timing of a nerve injury what do we mean by “the rule of three”?
- Clean or sharp? = immediate surgery within 3 days
- Blunt or contusion? = Early surgery within 3 wks
- Closed injury? = Delayed surgery within 3 months
We need to know if an injury is peripheral or central, how would you spot UMN vs LMN?
UMN:
- Weaker
- Increased tone
- Increased reflexes
- Clonus
- Babinski’s
LMN:
- Weaker
- Decreased Tone
- Decreased Reflexes
- Atrophy
