Nerve Injury Flashcards
Motor Unit
This is the anterior horn cell, the motor axon and the muscle fibres
Sensory Unit
The cell bodies are in the posterior dorsal root ganglian
Nerve fibres join to form
Anterior motor roots or posterior sensory roots.
Spinal nerves
Anterior and posterior roots combine to form a spinal nerve and exit the vertebral column via an intervertebral foramen
Peripheral Nerve
This is the part of the spinal nerve distal to the nerve roots.
Diameter of bundles of peripheral nerves
0.3-22 micrometers.
Structure of the peripheral nerve
The peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue. The Axons are coated with endoneurium and grouped into fascicles which are covered with perineurium and these are grouped together to form the nerve which is covered with epineurium.
Aa Fibres
15 microns, 60-100m/s. Large motor axons, muscle stretch and tension sensory axons
Ab fibres
12-14 microns, 30-60 m/s touch, pressure, vibration, and joint position sensory axons
Ag fibres
8-10 microns, 15-30m/s, gamma efferent motor axons
Ad Fibres
6-8 microns, 10-15 m/s, sharp pain, very light touch and temperature sensation
B fibres
2-5 microns, 3-10m/s sympathetic preganglionic motor fibres
C fibres
<1 micron, <1.5m/s, dull, aching and burning pain, temperature sensation
Different injury types
Compression, trauma, indirect due to avulsion or traction
Compression
Usually results due to entrapment. Carpal tunnel, sciatica and Mortons Neuroma
Carpal Tunnel Syndrome
This is when the median nerve is compressed at the wrist
Sciatica
This is when the spinal root is compressed by the intervertebral disc
Mortons Neuroma
Compression of the ditial nerve in the 2nd or 3rd webspace of the foot
Neurapraxia
When the nerve is stretched or bruised. This results in reversible conduction block due to local ischaemia and demyelination.
Axonotmesis
The endoneurium is intact, but disruption to the axon occurs. Results from massive stretch(15%), compression or direct blow. Wallerian degeneration follows. The prognosis is fair and sensory recovery is often better than motor.
Neurotmesis
Complete nerve division due to laceration or avulsion. There is no recovery at all unless the injury is successfully repaired. The endoneural tubes are disrupted so theres a high chance of “miswiring” during regeneration.
Closed nerve injury
This is associated with nerve injuries in continuity. Spontaneous recovery is possible but surgery is indicated after three months if no recovery is indicated by clinical or electromyography review. Axonal growth rate is 1-3mm/day. Common examples of closed nerve injury are brachial plexus injuries and radial nerve humeral fracture.
Open Nerve Injury
this is frequently related to nerve division (for example neurotmetic injuries with knives or glasses). This has to be treated early with surgery is repair is expected. The distal portion of the nerve undergoes Wallerian degeneration (occurs up 2 to 3 weeks after injury).
Sensory clinical features of nerve injury
dysaethesia (disordered sensation). This can be anaesthetic (numb), hypo and hyperaethetic, paraesthetic (pins and needles).
