Peripheral nerve injuries Flashcards
Define the motor unit (efferent) of a nerve
- Anterior horn cell (in gray matter of spinal cord)
- Motor axon
- Muscle fibres (NMJs)
Define sensory unit of a nerve
-Cell bodies in posterior root ganglia (lie outside spinal cord)
What do nerve fibres join to form?
- Anterior (ventral) motor roots
- Posterior (dorsal) sensory roots
Where do spinal nerves exit (formed by anterior and posterior roots combining)
Vertebral column via intervertebral foramen
What is the peripheral nerve?
- Part of spinal nerve distal to nerve roots
- Bundles of nerve fibres
- Diameter 0.3-22 micrometres
- Schwann cells form thin cytoplasmic tube around
- Larger fibres in multi layered insulating membrane (myelin sheath
Discuss the structure of peripheral nerves
- Axons coated with endoneurium, are grouped into
- Fascicles (bundles) covered with perineurium, are grouped to form
- Nerve, which is covered with epineurium
What different types of injuries to nerves can occur?
- Compression
- Trauma (direct/indirect)
What sort of examples are of compression of nerves?
- Carpal tunnel syndrome
- Sciatica
- Mortons neuroma
What examples of direct trauma to nerves are there?
- Blow
- Laceration
What examples of indirect trauma are there?
- Avulsion
- Traction
What is neurapraxia?
- Stretched or bruised, local ischaemia and demyelination (reversible conduction block)
- Nerve in continuity
- Prognosis good (wks/mths)
What is axonotmesis?
- Stretched/crushed/direct blow to nerve
- Endoneurium intact but axons disrupted (tube in continuity). More severe injury
- Wallerian degeneration follows
- Prognosis fair (sensory recovery often better than motor)
What is neurotmesis?
- Complete nerve division
- Laceration/avulsion
- No recovery unless repaired
- Prognosis poor
What grading is used to determine extent of nerve injury?
Sutherland grade (grade 5 worst)
Discuss closed nerve injuries and give examples
- Associated with nerve injuries in continuity (neuropraxis, axonotmesis)
- Spontaneous recovery possibly, surgery indicated after 3m (do EMG if no recovery)
Examples
- Brachial plexus injuries
- Radial nerve humerus fracture
Discuss open nerve injuries and give examples
- Related to nerve divsion (neurotmesis)
- Early surgery
- Eg knives/glass
Clinical features of nerve injury?
-Sensory
>Dysaethesiae
-Motor
>Paresis/paralysis
>Dry skin
-Reflexes
>Reduced/absent
Discuss healing of nerve injuries
- Slow
- Starts with initial axon death distal to injury (wallerian degeneration then degradation of myelin sheath)
- Proximal axon budding after 4d
What is the regeneration rate?
1mm/day. Pain modality first to return
What is tinels sign (can monitor recovery)
Tapping over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed
Nerve conduction studies can also monitor recovery
What two ways can surgery be used to repair nerves?
- Direct repair
- Nerve graft
What is rule of 3 for surgical timing in peripheral nerve injury?
- Immediate surgery within 3d for clean/sharp injuries
- Early surgery within 3w for blunt/contusion injuries
- Delayed surgery after 3m for closed injuries
