Peripheral nerve injuries Flashcards
The motor unit?
Motor unit (efferent):
> Anterior horn cell, (located in the gray matter of the spinal cord)
> Motor axon,
> Muscle fibres (neuromuscular junctions)
Sensory unit?
Sensory unit:
> cell bodies in posterior root ganglia
> I.e. lie outside the spinal cord
What do nerve fibres join to form?
Nerve fibres join to form:
> anterior (ventral) motor roots
> posterior (dorsal) sensory roots
Spinal nerves?
Spinal Nerves
> Anterior and posterior roots combine to form a spinal nerve.
> Exit the vertebral column via an intervertebral foramen.
Anterior/ventral nerve fibres?
Motor
Posterior/dorsal nerve fibres?
Sensory
What is considered a peripheral nerve?
Nerves distal to spinal nerve roots
What is the diameter of peripheral nerves?
Range in diameter from 0.3-22um
What are peripheral nerves?
A peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue
What are axons?
AXONS = Long processes of neurones
What are axons covered in?
Endoneurium
What are fascicles?
Nerve bundles
What are fascicles covered in?
Perineurium
What is a nerve covered in?
Epineurium
What are neurones surrounded by?
Schwann cells
Role of Aα, Group IA and IB afferents nerve fibres?
> Large motor axons
> Muscle stretch and tension sensory axons
Role of Aβ, Group II afferents nerve fibres?
Touch, pressure, vibration and joint position sensory axons
Role of Aγ nerve fibres?
Gamma efferent motor axons
Role of Aδ, Group III afferents
nerve fibres?
Sharp pain, very light touch & temperature sensation
Role of group B fibres?
Sympathetic preganglionic motor axons
Role of Group C, Group IV afferents nerve fibres?
Dull, aching, burning pain and temperature sensation
Types of injury to peripheral nerves?
> Compression - “Nerve palsies in the limbs” ]
> Trauma - direct (blow, laceration) or indirect (avulsion, traction)
- Neurapraxia
- Axonotmesis
- Neurotmesis
> Entrapment
Examples of classical conditions with peripheral nerve entrapment?
> Carpal tunnel syndrome
Median nerve at wrist
> Sciatica
Spinal root by intervertebral disc
> Morton’s neuroma
(digital nerve in 2nd or 3rd web space of forefoot)
What is neuropraxia?
NEURAPRAXIA -
> nerve in continuity
> stretched (8% will damage microcirculation) or bruised
> reversible conduction block - local ischaemia and demyelination
> prognosis good (weeks or months)
Examples of types of direct trauma to peripheral nerve?
Blow or laceration
Examples of types of indirect trauma to peripheral nerve?
Avulsion or traction
Axonotemesis?
> endoneurium intact (tube in continuity), but disruption of axons; more severe injury
> stretched ++ (15% elongation disrupts axons) or crushed or direct blow
> Wallerian degeneration follows
> prognosis fair (sensory recovery often better than motor - often not normal but enough to recognise pain, hot & cold, sharp & blunt)
Can peripheral nerves regenerate?
Yes, around 3mm per day
Neurotmesis?
> complete nerve division
> laceration or avulsion
> no recovery unless repaired (by direct suturing or grafting)
> endoneural tubes disrupted so high chance of “miswiring” during regeneration
> prognosis poor
Sunderland grading for peripheral nerve damage?
Grade 1 = Neuropraxia Grade 2 = Axonotmesis Grade 3 = Neurotmesis Grade 4 = Neurotmesis + Grade 5 = Neurotmesis ++
Closed peripheral nerve injuries?
Associated with nerve injuries in continuity
> neuropraxis
> axonotmesis,
Examples:
> Typically stretching of nerve:
- brachial plexus injuries
- Radial Nerve humeral fracture
How are closed peripheral nerve injuries managed?
> spontaneous recovery is possible
> surgery indicated after 3 months if no recovery is identified:
Clinical - Tinel’s test
Electromyography
How are open peripheral nerve injuries managed?
Frequently related to nerve division:
> neurotmetic injuries
> E.g. knives /glass
Distal portion of the nerve undergoes Wallerian degeneration
> Occurs up 2 to 3 weeks after the injury
What usually occurs 2-3 weeks after open peripheral nerve injuries?
Wallerian degeneration
How are open peripheral nerve injuries managed?
Treated with early surgery
Clinical features in nerve injury - Sensory?
Dysaethesiae (disordered sensation)
> anaesthetic (numb)
> hypo- & hyper-aesthetic
> paraesthetic (pins & needles)
Clinical features in nerve injury - Motor?
> paresis (weakness) or paralysis ± wasting
> dry skin = loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
Clinical features in nerve injury - reflexes?
Diminished or absent
Following nerve injury how long does it take for proximal axonal budding to occur?
4 days
During healing of peripheral nerve what is the regeneration rate?
1mm/day (3-5mm/day in children)
During healing of peripheral nerve what is the first modality to return?
Pain
During healing of peripheral nerve what determines prognosis?
> whether nerve is
- “pure” (only sensory or only motor)
- “mixed” (both sensory and motor within same nerve)
> how distal the lesion is (proximal worse)
During healing of peripheral nerve what test(s) are used to monitor recovery?
> Clinical - Tinel’s sign = tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed
> Electrophysiological Nerve Conduction Studies
How can peripheral be repaired?
Direct Repair > Laceration > No loss nerve tissue > Microscope/Loupes > Bundle repair > Growth factors
Nerve Grafting > Nerve loss > Late repair: - (retraction) - Sural nerve
What is meant by the “Rule of Three” in nerve injuries?
Surgical timing in a traumatic peripheral nerve injury
1) Immediate surgery within 3 days for clean and sharp injuries
2) Early surgery within 3 weeks for blunt/contusion injuries
3) Delayed surgery, performed 3 months after injury, for closed injuries.
UMN versus LMN - Strength?
UMN = Decreased LMN = Decreased
UMN versus LMN - Tone?
UMN = Increased LMN = Decreased
UMN versus LMN - Deep tendon reflexes?
UMN = Increased LMN = Decreased
UMN versus LMN - clonus?
UMN = Present LMN = Absent
UMN versus LMN - Babinski’s sign?
UMN = Present LMN = Absent
UMN versus LMN - Atrophy?
UMN = Absent (Or small) LMN = Present, large loss
