Peripheral nerve injuries Flashcards
What diameter do peripheral nerves range from
0.2-22 um
What coats the axons
Endonurium
What coats the fascicles
Perineurium
What coats the nerve itself
Epineurium
What are Aa function
Large motor axons
Muscle stretch
Tension sensory axons
What are Ab function
Touch
Pressure
Vibration
Joint sensory position
What are Ay function
Gamma efferent motor axons
What are A (delta) function
Sharp pain
Very light touch
Temperature sensation
What are B function
Sympathetic preganglionic motor axons
What are C function
Dull, aching burning pain
temperature sensation
How can injury to a peripheral nerve occur
Compression
trauma
What can compress nerves
Nerve entrapment
Compression conditions
What are Classical compression conditions
Carpal tunnel syndrome
Sciatica
Morton’s neuroma
What is compressed in carpal tunnel syndrome
median nerve
What is compressed in sciatica
Spinal root compression by intervertebral disc
What is compressed in mortons neuroma
digital nerve in 2nd or 3rd web space of forefoot are compressed in sole of foot)
What nerve damage can trauma cause
- Neurapraxia
- Axonotmesis
- neurotmesis
What is neupraxia
- Nerve in continuity in neuropraxia.
- Stretched (8% will damage microcirculation) or bruised
- You get a Reversible conduction block due to local ischaemia and demyelination
- For a short area in the nerve you cannot get conduction.
- Prognosis good (weeks or months)
What is axonotmesis
- Endoneurium intact (tube in continuity), but disruption of axons within it;
what causes axonotmesis
- Can occur by the nerve being stretched (15% elongation disrupts axons) or severly crushed or direct blow
What is pathophysiology of axonotmesis
- Wallerian degeneration follows (distal to sight of injury. The nerve fibre disappears but the endoneurial tube remains. Proximally the nerve shrinks back to the last node of ranvier.
what is prognosis of axonotmesis
- Prognosis fair (sensory recovery often better than motor - often not normal but enough to recognise pain, hot & cold, sharp & blunt)
What is Neurotmesis
- Complete nerve division and loss of endoneurium (possibly perineurium)
What typically causes Neurotmesis
Laceration or Avulsion
What is prognosis of Neurotmesis
Poor prognosis
No recovery unless repaired (by direct suturing or grafting)
What are closed nerve injuries
Neuropraxis
axonotmesis,
What is treatment for closed nerve injuries
Surgery indicated after 3 months if it has not recovered
If no recovery is identified
- Clinical
- Electromyography-
What is the Axonal growth rate
Axonal growth rate (1–3 mm/day)
What are open nerve injuries
Neurotmesic injuries
what is wallerian degeneration
Changes (death) of axons distal to the sight of a nerve injury
What are motor changes seen in nerve injury
- Paresis (weakness) or paralysis ± wasting
- Dry skin
o Loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
What are sensory changes in a nerve injury
- Dysaethesiae (disordered sensation) o Anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)
What happens about 4 days after a peripheral nerve injury
Proximal axonal budding occurs after about 4 days
What does the Prognosis for recovery depend on:
- whether nerve is
o “pure” (only sensory or only motor)
o “mixed” (both sensory and motor within same nerve) - how distal the lesion is (proximal worse)
Does a pure nerve or mixed nerve have a better prognosis
pure nerve tends ro receoer better because in general even if there is miswiring and they grow and miss their own tube but grow down to antoher oenen. They will all grow down to motor end plates of sensory end plates
Why do mixed nerves have a worse prognosis
mixed nerves have a variable recovery as the senory nerves (some) can gorw back down the motor tubes and the motor axons down the sensry tubes and you will therefore get a much more imcomplete recovery.
Why does the nerve recover better if the injury is more distal
Distal better recovery due to the 1mm growth a day. If it’s a long distance to grow back down then you get degeneration of the endplates to when the nerve gets to the end plate it doesn’t function as well.
What can be used to monitor recovery of a nerve
Tinnel’ sign
Electrophysiological Nerve Conduction Studies
