Nerve Healing & Grafting Flashcards
1
Q
What determines the conduction velocity of a nerve action potential?
A
- diameter of axon
- presence of myelin
2
Q
What are schwann cells
A
- Glial cells surrounding axons, are myelinated or non-myelinated
- Function:
- trophic factor release
- support regneration
- antigen presentation
3
Q
Define the structural organization of a nerve
A
- Endoneurium: encases axon and their gial cells
- Perineum: encases group of axons into a fascicle
- Epineurium
- EpiFascicular - internal - surrounds group of fascicles
- Epineurial - external - surrounds nerve trunk
- Mesoneurium - external vascular network and permits gliding
4
Q
What is Wallerian degeneration
A
Distal degeneration of axon leaving behind scaffold of schwann cells
Proximal degeneration varies with degree of injury
5
Q
Classify nerve injury
A
- Neuropraxia - focal segmental demyelination. Tinels (-), Recovery complete days-wks
- Axonotmesis - axon damaged + Wallerian degenration, Tinels (+) progresses, Recovery complete wk-mths
- Axonotmesis - axon, endoneurium damaged, Tinels (+) progresses, Recovery variable
- Axonotmesis - axon endoneurium perineurium damaged, Tinels + BUT no progression, No recovery=> NIC
- Neurotmesis - complete never transection, Tinels + no progression, Neuroma
- Mixed nerve injury
6
Q
How do nerves heal
A
- Injury occurs then events occur at body and stumps
- @ Cell body
- cell swells and NT production reduces
- 2wks later, cell returns to producing structural proteins and axoplasm flow begins again
- @ proximal stump
- minimal wallerian degeneration to netx proximal node of ranvier
- Axonal spouts with filopdia and growth cones start wihtin 24hrs
- Filopodia attracted to trophic factors of distal stump. Once in endoneurial scaffold, optimal location for growth and beomes parent nerve
- RLS in neuroregeneratio is axonal transport
- 4-400mm/day.
- Regeneration 1mm/day after 30day delay for clearance of cellular debris
- @ Distal stump
- Schwann cells phagocytose axoplasm/myelin and macrophage clear debris = empty endoneurial conduits
- conduits shrink if no growth wihtin a month
- Bands of bunger are scaffold of schwann cells ready for neuronal ingrowth
7
Q
What are systemic factors that inhibit nerve healing
A
- Vitamin deficiency
- Gout (colchicine inhibit tubulin)
- Alcohol
- DM
8
Q
What occurs to the end organs when nerve injury occurs
A
- Motor nerve injury
- Motor end plate increases number of AchR wihtin weeks of denervation
- = Denervation supersensitivity - lower memrbane potential and prone ot fibrillations
- Once reinnervated, AchR# normalize
- can babysit with another motor or sensory nerve until correct nerve reaches target
- at 12mths, muscle fibrosis limits function
- Sensory nerve injury
- Pacinian and Merkel degenerate but regain fx if renervated
- Meissner degeneratio is permenant after 6mth
- If delay of reinnervation >12mth, lose 2PD but may regain protective sensation
9
Q
What is an EMG and what information does it provide
A
- a depiction of muscle electrical activity by measuring electrical potential diff b/w 2sites
- MUAP : motor unit outcome potential where MU is muscle, NMJ, axon, Ventral horn
- MUAP activity described
- at rest, at needle insertion, volunteer activity
- amplitude, duration, rise time, phases
- Normal muscle shows small bursts of activity w needle insertion then stops. Abnormal muscle continues to fibrillate w needle insertion
10
Q
What is a NCS and what information does it provide
A
- describes the elctrical activity from peripheral nerves between sensory and motor nerves to end organ targets
- SNAP and CMAP
- SNAP amplitude for peak to peak area = # of nerve fibers stimulated
- CMAP amplitude = # of muscle fibers stimulated
- Measures of NCS include
- amplitude, conduction velsocity, duratio, configuration
- drop in amplitude = axon degeneration of SNAP/CMAP = wallerian degeneration
- drop in cv = Demyelination
- variation based on stimulation from distal to proximal = conduction block
11
Q
What is the purpose of intraop NCS?
A
To assess a NIC
- determine if any axons are viable through NIC
- If NAP are detected, an external and internal neurolysis will provide beenfit
- if no NAP detected, indicates need for NIC resection and reconstruction
12
Q
How long o dyou wait fo NCS and EMG studies following nerve injury?
A
- 6weeks
WHY?
- takes 6 wks for muscle AchR# to increase to demonstrate fibrillations if in fact nerve degeneration has occured
- takes 4 wks for wallerian degenration to occur
13
Q
List nerve repair types
A
- Epineurial - aligned via vasa nervosa
- Group Fascicular (inner epineural)
- Fascicular (perineural)
- End to side repair
- Nerve transfer
- Fibrin glue
- Laser
14
Q
List techniques to facilitate approaprite coaptation of fascicular group
A
- Anatomic landmarks - fascicle size, position, orientation, vasa nervosa
- Ecltrical Stimulation - possible up to 3days post injury
- Histochemical staining - Acestease Motor, CA Sensiry - possible up to 9 days post injury
15
Q
What are poor prognostic indicators for nerve repair result
A
INJURY M & M CPD
- Multi-level
- Avulsion/Crush/traction
- Mixed nerve < (Worse than pure sensory/pure motor)
- Concomitant ST vascular injury
- Proximal
- Devascularization
REPAIR
- Delayed
- Tension
PATIENT
- >40
- Compliance
