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Flashcards in Nerve Healing & Grafting Deck (24):
1

What determines the conduction velocity of a nerve action potential?

  • diameter of axon
  • presence of myelin

2

What are schwann cells

  • Glial cells surrounding axons, are myelinated or non-myelinated
  • Function:
    • trophic factor release
    • support regneration
    • antigen presentation

3

Define the structural organization of a nerve

  • 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

What is Wallerian degeneration

Distal degeneration of axon leaving behind scaffold of schwann cells

Proximal degeneration varies with degree of injury

5

Classify nerve injury

  1. Neuropraxia - focal segmental demyelination. Tinels (-), Recovery complete days-wks
  2. Axonotmesis - axon damaged + Wallerian degenration, Tinels (+) progresses, Recovery complete wk-mths
  3. Axonotmesis - axon, endoneurium damaged, Tinels (+) progresses, Recovery variable
  4. Axonotmesis - axon endoneurium perineurium damaged, Tinels + BUT no progression, No recovery=> NIC
  5. Neurotmesis - complete never transection, Tinels + no progression, Neuroma
  6. Mixed nerve injury

6

How do nerves heal

  • 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

What are systemic factors that inhibit nerve healing

  • Vitamin deficiency
  • Gout (colchicine inhibit tubulin)
  • Alcohol
  • DM

8

What occurs to the end organs when nerve injury occurs

  • 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

What is an EMG and what information does it provide

  • 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

What is a NCS and what information does it provide

  • 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

What is the purpose of intraop NCS?

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

How long o dyou wait fo NCS and EMG studies following nerve injury?

  • 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

List nerve repair types

  • Epineurial - aligned via vasa nervosa
  • Group Fascicular (inner epineural)
  • Fascicular (perineural)
  • End to side repair
  • Nerve transfer
  • Fibrin glue
  • Laser

14

List techniques to facilitate approaprite coaptation of fascicular group

  • 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

What are poor prognostic indicators for nerve repair result

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

16

How do nerve grafts heal

Same as skin grafts

  • Imbibition - diffusion -  for 3days
  • Inosculation - vascular reconnection day 3-6
  • Revascularization - day 6

17

What are types of nerve grafts

  • Trunk grafts: large grafts interposed in segment
    • get central fibrosis due ot prolonged time fo rrevascularization - not used
  • Cable grafts - multiple small segements to interpose - less fibrosis as greate SA for graft survival
  • InterFascicular graft - poor if gap >6cm
  • Free vascularized "graft" - larger # of myelinated axons- improved reinnervation if radiated/scarred bed
  • Nerve conduits - if <3cm

18

What are sources of nerve grafts

  • Autogenous
    • for defects >5cm
    • Nonvascularized
      • MABC, MBC, LABC, PIN, sural, med/lat CFN
      • portion fo damaged nerve
    • Vascularized
      • radial, ulnar, sural artery & nerve, deep peroneal-dorsalis pedis
  • Allografts
    • acts as scaffold
    • <30mm, 1-2mm diameter
  • Conduits
    • synthetic - silicone, PGA
    • biologic - vein

19

What is axogen

  • Axogen = decellularized cadaveric peripheral nerve scaffold
  • Processed: decellularized, radiated, enzyme degradation
  • keep at -40

20

How do you manage nerve repairs post-opeatively

  • Splint 3 weeks
  • Follow tinels sign
    • irritability of regenerating nerves not yet insulated by schwann cells
  • Outcomes
    • Motor - based on MRC
    • Sensory
      • deep pain
      • superficial pain and sensibility
      • superficial pain and touch
      • localization and some 2PD
      • complete recovery w 2PD (4-6mm)

21

What is a neuroma

Response of a nerve followiing trasnsection- sprouting axons regenrated outside of epineurium

Occurs only at the proximal end

22

What is  a glioma

 

Response ot nerve transection in the distal stump

23

Why is a neuroma painful

  • continuous chemical or mechanical irritation of axons
  • persistent activiation of axon through DRG

24

What are treatment options for a neuroma

NON-OP

  • PT, desensitization, medications

OPERATIVE

  • repair nerve +/- graft
  • place nerve end into muscle
  • resect and allow retraction into soft tissue
  • resect nerve and close over epineurium
  • relocate neroma away from pressure point