Nerve substitutes lecture
•Download as PPT, PDF•
3 likes•128 views
The document discusses options for overcoming nerve gaps during nerve reconstruction, including autografts, conduits, and allografts. Autografts are still considered the gold standard but have limitations. Modern biodegradable synthetic conduits can avoid donor site morbidity but evidence on their effectiveness is mixed. Vein and nerve allografts have shown promising results comparable to autografts in short nerve gaps under 3cm. Longer nerve gaps remain a significant challenge.
Recommended
More Related Content
What's hot
What's hot (20)
Similar to Nerve substitutes lecture
Similar to Nerve substitutes lecture (20)
More from Vaikunthan Rajaratnam
More from Vaikunthan Rajaratnam (20)
Recently uploaded
Recently uploaded (20)
Nerve substitutes lecture
- 1. Overcoming Nerve Gap (Review of allografts / conduits / wraps in nerve reconstruction) Sreedharan Sechachalam Hand and Microsurgery Section Tan Tock Seng Hospital Singapore
- 2. Factors determining prognosis following nerve injury • Nature of injury • Age • Level of injury • Type of nerve • Nerve gap • Condition of nerve ends • Delay between injury and repair
- 3. Nerve Repair / Reconstruction • Aim – Direct the regenerating nerve fibres into the appropriate distal endoneurial tube with minimal loss of nerve fibres at the injury site
- 4. Principles of Nerve Repair • Under magnification • Careful dissection & mobilisation • Adequate debridement • Correct orientation • Tension free • Skeletal stability, healthy bed
- 5. For all nerve transections: •Nerve stumps adequately debrided •‘Fascicular bloom’ •Punctate bleeding at cut ends •Associated joint ranged •Then, is there nerve gap? Safa B et al. Autograft substitutes. Hand Clin 2016
- 6. How to overcome nerve gap • Early repair • Mobilisation – Excessive mobilisation > ischemia • Transposition • Bone shortening • Grafts & Conduits
- 7. Nerve Reconstruction • Principle: To bridge the nerve gap & alleviate tension at coaptation site • Autografts • Conduits • Allografts
- 9. Donor Nerves Neligan – Plastic Surgery Sebastin & Chung – Operative techniques in hand surgery, 2nd ed **SRN – only used when there is a irrepairable prox nerve injury e.g. BPI - no expectation of functional recovery of sensation
- 10. Terminal branch of PIN • Floor of 4th extensor compartment • 5 cm (1-3 fascicles) • Ideal size for digital nerve defects • No loss of function
- 11. Autografts • Advantages – Biocompatible scaffold – Growth factors & adhesion molecules • Cons – Donor site morbidity (Surgical incision, sensory loss) – Limited source – Mismatch
- 12. Conduits • 1880s – Themistocles Gluck, Gustave Neuber • decalcified bone tubes for nerve reconstruction to allow the nerve to climb “…up the scaffold of the implanted foreign body as vine climbing a staff” • 1909 – Wrede – saphenous vein • 1982 – Chiu – autogenous nerve conduit • 1990 – Mackinnon & Delon - PGA iJpma et al (2008) The early history of tubulation in nerve repair Strauch (2013) Nerve conduits: an update on tubular nerve repair & reconstruction. JHS;38A:1252-55
- 13. Nerve Conduits • Avoid donor site morbidity • Creates isolated environment surrounding repair site • Contain cytokines • Protection from fibroblasts & inflammatory cells • Prevent mechanical obstruction • Guides sprouting axons Rivlin et al (2010) The role of nerve allografts and conduits for nerve injuries. Hand Clin;26:435-446
- 14. Conduits • Mode of action – Encases distal and proximal ends within tube and provides gross macroalignment for the nerve – Containment of fluid leaking from the nerve ends, gathering it within the chamber
- 15. (A)Protein-rich fluid (neurotrophic factors) (B)Fibrin-rich scaffold (C)Cell migration (perineurial, endothelial, Schwann cells) (D)Axonal cable elongates Kehoe et al (2012) FDA approved guidance conduits & wraps for peripheral nerve injury: A review of materials and efficacy. Injury, Int J Care Injured;43:553-72
- 16. Ideal conduit Characteristics •Biocompatible •No inflammatory response •Biodegradable •Flexible, soft •Guidance cue for extending growth cone •Semi-permeable •Retain secreted neurotrophic factors •Prevent fibrous tissue ingrowth into injury site
- 17. Ideal conduit Characteristics •Biocompatible •No inflammatory response •Biodegradable •Flexible, soft •Guidance cue for extending growth cone •Semi-permeable •Retain secreted neurotrophic factors •Prevent fibrous tissue ingrowth into injury site
- 18. Conduit materials • Silicone (nonpermeable, permanent) – Soft tissue irritation, fibrotic encapsulation, compression • Modern biomaterials (permeable, biodegradable) – Denatured collagen, polyesters – Permeable: diffusion of oxygen and micronutrients – First commercially available: Polyglycolic acid
- 19. Modern biomaterial conduits • Polyglycolic acid (PGA) (Neuratube®) – Rigid, thermoplastic polymer – High rate of degradation, acidic • Caprolactone (Neurolac®) – Degrades more slowly than PGA – Less acidic degradation products – Clear • Collagen (NeuraGen®) – semi-permeable Type 1
- 20. Evidence is confusing ... • PGA vs vein conduits – equivalent sensory recovery1 • Caprolactone vs primary repair – equivalent sensory recovery2 • PGA - improved sensory recovery compared to primary repair & autologous nerve graft (gaps ≤4mm or ≥8mm)3 • Collagen conduit vs autograft – comparable results, PGA conduits poorer4 • Caprolactone tubes – only 1/12 major nerve repair achieved good outcome5 1 Rinker & Liau (2011) Propsective randomized study comparing woven PGA & autogenous vein conduits for reconstruction of digital nerve gaps. J Hand Surg Am;36(5):775-81 2 Bertleff (2005) A prospective clinical evaluation of biodegradable neurolac nerve guides for sensory nerve repair in the hand. J Hand Surg Am;30(3):513-8 3 Weber et al (2000) A randomized prospective study of PGA conduits for digital nerve reconstruction in humans. Plast Reconstr Surg;106(5):1036-45 4 Waitayawinyu et al (2007) A comparison of PGA vs type 1 collagen bioabsorbable nerve conduits in a rat model: an alternative to autografting. J Hand Surg Am;32(10):1521-9 5 Chiriac et al (2012) Experience of using the bioresorbable copolyester nerve conduit Neurolac for nerve repair in peripheral nerve defects. J Hand Surg Eur;37(4):342-9
- 21. Summary of evidence: Synthetic conduits • Most studies are with digital nerves – < 10mm, good results --- recommendation – > 30mm, bad results • Major peripheral nerves – Paucity of nonsponsored studies – Mixed results Safa B et al. Autograft substitutes. Hand Clin 2016
- 23. Vein conduits • Superficial veins, gaps<3cm • Equivalent results to nerve autograft1,2 • Equivalent results to PGA, fewer complications3 1 Calcagnotto & Silva (2006) The treatment of digital nerve defects by the technique of vein conduit with nerve segment. A randomised prospective study. Chir Main;25(34):126-30 2 Chiu & Strauch (1990) A prospective clinical evaluation of autogenous vein grafts used as a nerve conduit for distal sensory nerve defects of 3cm or less. Plast Reconstr Surg;86:928-34 3 Rinker & Liau (2011) Prospective randomized study comparing woven PGA & autogenous vein conduits for reconstruction of digital nerve gaps. J Hand Surg Am;36(5):775-81
- 24. Nerve Allograft • Allograft from cadaver donors • Attractive option – Benefits of conduits (size match, no donor deficit, large supply) – Ideal microenvironment for nerve healing (microarchitecture, neurotrophic factors, guidance cues) • Disadvantages: – Cost – Immunosuppressive treatment • Technique as for autograft
- 25. Nerve allograft: Addressing the disadvantages • Tissue engineering – Extracts MHCs, myelin, cellular debris • >>> reduces immunogenecity and need for immunosuppression • Unfortunately, these limits the regenerative capacity as well • Cost – ? Exchanging cost of operating theatre for cost of product (with all the other benefits)
- 28. Summary of results: Allografts • Digital nerves – Up to 30mm gap: Good results (at least 6mm 2PD) – Up to 70mm gap: Meaningful recovery • Major peripheral nerves – Promising – Up to 100mm gap Safa B et al. Autograft substitutes. Hand Clin 2016
- 29. Nerve wraps • Following nerve repairs / neurolysis • Protect the repair site from adhesion formation • Vein / Synthetic • Synthetic: Selective permeability allowing nutrient diffusion while blocking fibroblast migration Orthopaedics 2017
- 30. Safa B et al. Autograft substitutes. Hand Clin 2016
- 31. Summary •Transected nerve – Debridement of ends – Judiciously attempt to overcome nerve gap – If necessary, nerve reconstruction – Options: Autograft, conduit, allograft
Editor's Notes
- Approach good exposure of whole zone of injury Remove scar tissue Nerve ends Mushrooming-sign of transected viable axons that will be able to sprout after construction, indicates nerve is suitable recipient for nerve graft Gap Calculate maximum gap to be bridged, in relation to any movement of joint later on Calculate gap with IPJ joints in full extension ?is it possible for primary repair? Length of graft Should be 15% longer than maximum gap due to shrinkage Consider nerve excursion Length best assessed with all adjacent joints fully extended Harvest of graft Size of nerve trunk to be bridged To decide which donor nerve to take Donor site morbidity & functional deficit Gentle handling Keep it moist in saline soaked gauze Cut sharp, remove few mm of extra epineurium from ends of graft (6) Coaptation & maintenance nerve graft preferably reversed at time of placement to decrease risk of diversion of regenerating axons through these cut off branches Depending on size of nerve trunk, suture whole nerve or individual fascicles 9/0 or 10/0 nylon Fibrin glue as adjunct Sufficient number of fascicles, one cable for each severed group of fascicles Coaptation not too tight as it can lead to crumpled nerve endings Fibrin glue reinforce and lessen risk of separation between graft and nerve endings, can give better matche between graft and nerve end If multiple cables used, individual grafts positioned so that they do no adhere too closely to each other Allow diffusion of oxygen and other nutrients Allow for rapid revascularisation from recipient bed Vialbility of tissue bed is crucial for optimal survival of schwann cells & successful axonal regeneration Splint (dorsal) – IPJ neutral, MCPJ 50-60 degrees flexion 2-3/52
- Nerve ischaemia &gt; increased generation of connective tissue blocking axonal regeneration Acute stretching&gt;intraneural haemorrhage&gt;scar formation Scar maturation&gt;compress nerve fibres&gt;neuroma formation
- Autologous nerve grafts gold standard compared to artificial conduits -neovascularization occur thru capillary ingrowth from the periphery & nerve ends -smaller nerves revascularise easily (sural, medial and lat antebrachial cutaneous ) -thicker nerves have risk of central necrosis and scarring as a result of poor diffusion -one cable when smaller nerves bridged -multiple cables may be required to bridge the gap in larger nerve trunks
- Provide a biocompatible scaffold containing both Schwann cells & their basal lamina Promote regeneration through natural production of growth factors & adhesion molecules, which help stimulate neurite elongation and direction on site
- -Themistocles Gluck – German surgeon (Berlin) – first joint replacement of a tuberculous knee joint with ivory -Gustave Neuber – German surgeon – developed decalcified bone tube for wound drainange -Wrede – use saphenous vein to bridge human median nerve gap 1941-Swan reconstructed an ulnar nerve gap 1982-Chiu reported successful experimental nerve reconstruction using autogenous nerve condiuts 1990 – Mackinnon & Dellon – encouraging clinical results using PGA tubes for nerve gaps less than 3 cm
- -isolated environment around repair site – contain the needed cytokines for nerve regeneration -protects repair site from fibroblast and inflammatory cell penetration -prevent mechanical obstruction from intruding between regenerating nerve ends -guides axon sprouts to counterpart
- After implantation of conduit: Fluid secreted from nerve ends Gradient of neurotrophic factors Fibrin matrix creates scaffolding for cells (aid axonal growth) Nerve fibers begin to cross gap Superstructure of fibers 6th week: nerve fibers matured, macrophages disappearCompletion of nerve regeneration
- -caprolactone – poly-DL-lactide-E-caprolactone PGA – 90 days after implantation to degrade and get absorbed Caprolactone – clear allows direct visulaization Collagen – 8 to 48 months for complete biodegradation
- Rinker (2011) – n=68 -prospective randomized study comparing autogenous vein nerve conduits with PGA conduits for digital nerve gaps 4 to 25mm -looked at sensory recovery at 6 & 12 months Bertleff (2005) n=34 Weber n=128 Waitayawinyu n=45 -sciatic nerve of rats-looked at isometric muscle contraction force, axonal force -10mm gap Chiriac – 8 of 23 patients had complications such as extrusion of graft and fistulization, neuroma
- Rinker – 42 patients with76 nerve repairs-sensory recovery of vein conduit & PGA equivalent-lower complications