Peripheral Nerve Injuries Flashcards
What is motor (efferent) composed of?
- Anterior horn cell, (located in the gray matter of the spinal cord)
- Motor axon,
- Muscle fibres (neuromuscular junctions)
What is a sensory unit composed of?
Cell bodies in the posterior root ganglia (lie outside the spinal cord)
What do nerve fibres join to form?
- Anterior (ventral) motor roots
- Posterior (dorsal) sensory roots
How are spinal nerves formed?
- Anterior and posterior roots combine to form a spinal nerve.
- Exit the vertebral column via an intervertebral foramen.
What are peripheral nerves?
- The part of a spinal nerve distal to the nerve roots
- A highly organised structure comprised of nerve fibres, blood vessels and connective tissue
Describe the structure of peripheral nerves.
- Bundles of nerve fibres.
- Range in diameter from 0.3-22 μm.
- Schwann cells form a thin cytoplasmic tube around
- Larger fibres in a multi-layered insulating membrane (myelin sheath).
- Multiple layers of connective tissue surrounding axons
How are peripheral nerves formed?
AXONS (long processes of neurones) are coated with endoneurium and grouped into FASCICLES (nerve bundles ) covered with perineurium; these are grouped to form the NERVE which is covered with epineurium
What is the function of Aa (group IA and IB afferents) fibres?
- Large motor axons
- Muscle stretch and tension sensory axons
What is the function of AB (group II afferents) fibres?
Touch, pressure, vibration and joint position sensory axons
What is the function of Ay fibres?
Gamma efferent motor fibres
What is the function of Ad (group III afferent) fibres?
Sharp pain, very light touch and temperature sensation
What is the function of B fibres?
Sympathetic preganglionic motor axons
What is the function of C fibres?
Dull, aching, burning pain and temperature sensation
What can compression at different levels result in?
Nerve palsies
How can a nerve be injured?
- Compression
- Trauma (direct or indirect)
What types of trauma can occur to a nerve?
- Neurapraxia
- Axonotmesis
- Neuromesis
What is neurapraxia?
- Reversible conduction block (local ischaemia and demyelination)
- Nerve is stretched or bruised
- -Affects nerve in continuity
- Prognosis is good
What is axonotmesis?
- Rupture of axons within an intact endoneurium
- Stretched or crushed or direct blow
- Wallerian degeneration follows
- Prognosis fair sensory>motor
Can peripheral nerves regenerate?
YES
What is neurotmesis?
- Complete severance of a peripheral nerve by laceration or avulsion
- No recovery unless repaired (direct suturing or graft)
- Endoneural tubes disrupted so high chance of miswiring during regeneration
- Prognosis is poor
What grading system is used for peripheral nerve injury?
Sunderland grading
What is the Sunderland grades?
- Grade 1 Neuropraxia
- Grade 2 Axonotmesis
- Grade 3 Neurotmesis with intact perinerium
- Grade 4: Neurotmesis with intact epineurium
- Grade 5: Neurotemesis with complete severance of all layers
What are closed injuries associated with?
- Neuropraxis
- Axonotmesis
What are the outcomes like for closed injuries?
- Spontaneous recovery is possible
- Surgery is indicated after 3 months
- Axonal growth rate 1-3mm/day
What are typical examples of closed injuries?
Typically stretching of a nerve
- Brachial plexus injuries
- Radial nerve humeral fracture
What are open injuries frequently related to?
Neurotmetic injuries i.e. injured with knives or glass
How are open injuries treated?
Early surgery
What happens to the distal portion of the nerve in open injuries?
Undergoes Wallerian degeneration
-Occurs up to 2-3 weeks after the injury
What are the clinical features of nerve injury?
Sensory
-Dysesthesia (anaesthesia, hypo and hyper aesthetic, paraesthesia)
Motor
- Paresis or paralysis and wasting
- Dry skin (loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin)
Reflexes
-Diminished or absent
How does peripheral nerve healing occur?
- Very slow process
- Starts with initial death of axons distal to site of injury (Wallerian degeneration) then degradation of the myelin sheath
- Proximal axonal budding occurs after about 4 days
- Regeneration proceeds at rate of about 1mm/day
What is the first modality to return as a nerve heals?
Pain
What does the prognosis for recovery depend on?
Whether the nerve is
- Pure
- Mixed
How distal the lesion is
-Proximal is worse
How can recovery from a nerve injury be monitored?
- Tinel’s sign
- Electrophysiological nerve conduction studies
What is Tinel’s sign?
Tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed
How is a direct nerve repair carried out?
- Used for lacerations
- No loss of nerve tissue
- Microscope/loupes
- Bundle repair
- Growth factors administeered
How is nerve grafting carried out?
- Results in nerve loss
- Late repair
What is the rule of 3 in the surgical timing in a traumatic peripheral nerve injury?
- Immediate surgery within 3 days for clean and sharp injuries
- Early surgery within 3 weeks for blunt/contusion injuries
- Delayed surgery, performed 3 months after injury, for closed injuries.
How to tell the difference between peripheral and central nerve injuries clinically?
UMN vs LMN clinical signs
UMN lesion: Strength
Decreased
UMN lesion: Tone
Increased
UMN lesion: Deep tendon reflexes
Increased
UMN lesion: Clonus
Present
UMN lesion: Babinski’s sign
Present
UMN lesion: Atrophy
Absent
LMN lesion: Strength
Decreased
LMN lesion: Tone
Decreased
LMN lesion: Deep tendon reflex
Decreased
LMN lesion: Clonus
Absent
LMN lesion: Babinski’s sign
Absent
LMN lesion: Atrophy
Present
