Peripheral nerve injuries Flashcards
What is the structure of a motor unit?
Anterior horn cell in grey matter of spinal cord
Motor axon
Muscle fibres
What are the roots formed by nerves?
Ventral motor roots
Dorsal sensory roots
What is the structure of peripheral nerves?
Schwann cells form a thin cytoplasmic tube around
Axons coated with endoneurium and grouped into fascicles, which are coated in perineurium and groups to form the nerve which is coated in epineurium
What are the causes of nerve injury?
Compression
Trauma
What causes nerve compression?
Entrapment
Carpal tunnel
Sciatica
Morton’s neuroma
What are the types of nerve trauma?
Neuropraxia
Axonotmesis
Neurotmesis
What is neuropraxia?
Nerve stretched <8% or bruised
Reversible conduction block caused by local ischaemia
What is the prognosis for neuropraxia?
Good
What is axonotmesis?
Endoneurium intact but disruption of axons
Nerve stretch <15%, crushed or had direct blow
Wallerian degeneration follows
What is the prognosis for axonotmesis?
Fair
Sensory recovery often better than motor
What causes neurotmesis?
Laceration or avulsion
What is neurotmesis?
Disruption of endoneural tubes
What is the prognosis for neurotmesis?
Poor
No recovery unless repaired
What are the clinical feature of peripheral nerve injury?
Sensory- dysaethesia, anaesthesia, paraesthesia, hyper/hyperaesthesia
Motor- paresis, paralysis +/- wasting, dry skin
Reflexes decreased or absent
What is normal healing of nerves?
Very slow, starting with initial death of axons distal to site of injury
Regeneration ~1mm a day
Pain first to return
