Musculoskeletal Growth/Injury and Repair - Nerve Flashcards
What is an axon?
Long processes of neurones coated with endoneurium
What are fascicles?
Nerve bundles (groups of axons) covered with perineurium
What are nerves?
Groups of fascicles covered in epineurium
What are peripheral neurones surrounded by?
Schwann cells
What are the fiber types and functions?
SAVED AS FIBER TYPES AND FUNCTIONS
How can nerves be injured?
- Compression
* Trauma - direct (blow, laceration) or indirect (avulsion, traction)
What can nerve compression also be known as?
Nerve entrapment
What are the classical nerve compression conditions (3)?
- 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 are the 3 types of trauma nerve injury?
•Neurapraxia
•Axonotmesis
•Neurotmesis
SAVED AS NERVE TRAUMA
What is neurapraxia?
- Nerve in continuity
- Stretched (8% will damage microcirculation) or bruised
- Reversible conduction block - local ischaemia and demyelination
- Prognosis good (weeks or months)
What is axonotmesis?
- 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)
What is 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
What are the 2 classifications of nerve injury?
Open or closed
Describe closed nerve injuries?
•Associated with nerve injuries in continuity - neuropraxis
axonotmesis,
•Spontaneous recovery is possible
•Surgery indicated after 3 months
•If no recovery is identified - clinical, electromyography
•Axonal growth rate (1–3 mm/day)
•Examples - Typically stretching of nerve
e.g. brachial plexus injuries
or radial nerve humeral fracture
Describe open nerve injuries?
•Frequently related to nerve division - neurotmetic injuries
E.g. knives /glass
•Treated with early surgery
•Distal portion of the nerve undergoes Wallerian degeneration - occurs up 2 to 3 weeks after the injury
What are the sensory features of peripheral nerve injury?
- Dysthaesiae (disordered sensation) e.g.
- Anaesthestic - numb
- Hypo/hyper-aesthetic
- Paraesthetic - pins and needles
What are the motor features of peripheral nerve injury?
- Paresis (weakness) or paralysis ± wasting
* Dry skin - loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
What are the reflex features of peripheral nerve injury?
•Diminished or absent
How well do nerve injuries heal?
•Slow
•Starts with initial death of axons distal to site of injury - Wallerian degeneration
and then degradation myelin sheath
•Proximal axonal budding occurs after about 4 days
•Regeneration proceeds at rate of about 1 mm/day (or 1 inch/month) - poss. 3-5 mm/day in children
What is the first modality to return after nerve injury?
Pain
What factors affect the prognosis for nerve recover (2)?
- Whether nerve is pure of mixed
* How distal the lesion is - proximal worse
What sign can monitor nerve hearing?
Tinel’s - tap over nerve to see how distally nerve regeneration has progressed
What are electrophysiological nerve conduction studies?
A way of assessing injury and recovery of nerve injury
How are clean and sharp nerve injuries treated?
Immediate surgery within 3 days
How are blunt/contusion nerve injuries treated?
Early surgery within 3 weeks
How are closed nerve injuries treated?
Delayed surgery, performed 3 months after injury
How do you tell if a nerve injury is peripheral or central?
SAVED UNDER PERIPHERAL OR CENTRAL
How can nerves be repaired (2)?
- Direct repair
* Nerve grafting
How are nerves directly repaired?
- When laceration with 2 nerve endings close together with no loss of nerve tissue
- Done using microscope or loupes
- Nerve bundles repaired
- Growth factors not in routine use
How are nerves repaired using grafting?
- Where there is loss of nerve or retraction of nerve (cannot be pulled together in late repair)
- Sural nerve used to provide “tubes” - not a particularly useful nerve
What does Babinski’s sign indicate? PLANTAR REFLEX
UPM damage
