Nerve Flashcards
What is the anatomy of peripheral nerve?
nerve trunk endonerium nerve fibre motor neuron sensory neuron
How are sensory neurones and motor neurones linked?
1) sensory nerve from tendon organ
2) inhibitory interneuron
3) spinal cord
4) alpha motoneuron
5) muscle
Does adult PNS have capacity for regeneration?
Yes
Many neurotrophic factors are known
Return of normal function is rare. Motor & sensory deficits common
How does a peripheral nerve regenerate after injury?
1) Tip of nerve stump swells
2) Severed axons retract several mm
3) Proximal axons sprout vigorously after several days
4) Growth cones emerge from proximal axon along adhesive terrain
5) Growth cones elicit numerous extensions – fillapodia
6) Fillapodia extend outwards in all directions
7) The first fillapodium to reach an appropriate terrain survives
8) All other fillapodia die back
9) Distal nerve stump undergoes Wallerian 10) Degeneration (WD)
WD – axon degradation and
11) Schwann cell proliferation
13) Schwann cells organise in ordered columns
Columns referred to as bands of Büngner
Schwann cells provide optimal conditions for growth cone adhesion
What are the three main clinical strategies to repair gap injuries?
1) Suturing together proximal and distal ends \+ ‘Clean' transection injury - Tension in sutures 2) Autografting \+ Good reinnervation - Donor site morbidity 3.Nerve guidance conduits \+ Biocompatible materials - Primitive design - Limited regeneration
Why is surgical repair necessary for neural regeneration?
- Negligible repair in absence of surgical reconnection
- Early surgical repair used crude materials
Catgut, silk, cotton, metal wire - Frequently failed due to poor sterilisation techniques and inadequate sterilisation of implanted material
- 1950 & 60s – Coaptation was refined (end-to-end repair)
Surgical microscope, finer suture materials & instrumentation
How is epineural repair carried out?
- Fine polyamide sutures are placed through the epineural connective tissue
- Important to avoid underlying nerve tissue
How is facicular ot perineural repair carried out?
- Fine sutures are placed through the perineural connective tissue
- Significantly no better than epineural repair
How are nerve autografts carried out surgically?
- Used when nerve retraction or loss prevents end-to-end repair
- Used when reapproximation causes tension along suture line
- Patient’s sural nerve is interposed between damaged ends
What are the limitations of nerve autografts for injury repair?
Poor motor & sensory recovery
Limited nerve availability
Donor site co -morbidity
What size does the nerve gap injury need to be to need a nerve autograft>
> 2cm
What are examples of nerve guidance channels?
1) Integra Life Sciences NeuraGen™ nerve guide
=absorbable semi-permeable collagen tube
2) SaluMedica’s SaluBridge™ nerve cuff
=flexible tubular sheath made from silicone
How do nerve guidance channels (NGC) lead to neural regeneration?
Cylinders used to entubulate cut nerves
1800s to 1950s saw use of bone, collagen membranes, arteries and veins
Limited clinical usage
Poor choice of materials provided no useful clinical benefit
WW I & II saw use of parchment paper, tantalum, magnesium, rubber and gelatin
Limited biocompatibility caused tissue inflammation / rejection
1980s to present
Use of biocompatible materials enables moderate regeneration
What are the main characteristics of a conduit for nerve gap repair?
1) permissive microenvironment
2) bioresorbable
3) biocompatible
4) clinically applicable
5) beneficial to nerve regeneration
What are the advantages of NGCs?
1) Surgical repair is simplified
2) Tension at suture line is reduced
3) Scar tissue invasion is prevented
4) Outgrowing tissue is guided
5) Endogenous neuroactive molecules are sequestered
6) External inhibitory molecules are repelled
