Skin graftsw


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Skin graftsw

  1. 1. Physiology of Skin Grafts
  2. 2. SKIN: Physiology & Function• Epidermis: – protective barrier (against mechanical damage, microbe invasion, & water loss) – high regenerative capacity – Producer of skin appendages (hair, nails, sweat & sebaceous glands)
  3. 3. SKIN: Physiology & Function• Dermis: – mechanical strength (collagen & elastin) – Barrier to microbe invasion – Sensation (point, temp, pressure, proprioception) – Thermoregulation (vasomotor activity of blood vessels and sweat gland activity)
  4. 4. SKIN: Physiology & Function• Immunological surveillance• Most skin is thin, hair-bearing, has sebaceous glands• Skin of palms/soles/flexor surface of digits is thick, not hair-bearing, no sebaceous glands• Vascular supply confined to dermis
  5. 5. SKIN: Anatomy
  6. 6. SKIN: Anatomy
  7. 7. Skin Grafts: Classification• Full thickness skin grafts: - epidermis & full thickness of dermis• Split skin graft: - epidermis & a variable proportion of dermis - thin, intermediate or thick
  8. 8. Skin Grafts: SSG
  9. 9. Skin Grafts: Classification Autografts Isografts Allografts Xenografts
  10. 10. Skin Grafts: “Process of Take”• Vascularity of donor site• Tolerance to ischaemia• Metabolic activity of the graft
  11. 11. Skin Grafts: “Process of Take”• 4 Phases: – Fibrin adhesion – Plasmatic imbibition – Revascularization: Inosculation & capillary ingrowth – Remodelling: Revascularization & fibrous attachment in restoring normal histological architecture
  12. 12. Skin Grafts: “Process of Take”• Plasmatic Imbibition: – Initially graft ischaemic (24 – 48 hrs) – Fibrin adhesion – Imbibition allows the graft to survive this period – ? Important for nutrition of graft – ? Stops drying out
  13. 13. Skin Grafts: “Process of Take”• Inosculation & capillary ingrowth: – At 48 hrs – Through fibrin layer – Capillary buds from recipient bed contact graft vessels – Open channels (neo-vascularization)  pink graft
  14. 14. Skin Grafts: “Process of Take”• Revascularization & fibrous attachment: – Connection of graft & host vessels via anastomoses (inosculation) – Formation of new vascular channels by invasion of graft (neovascularisation) – Combination of old & new vessels (revascularisation) – Fibroblast proliferation: conversion of fibrin adhesion  fibrous tissue attachment (anchorage within 4 days)
  15. 15. Skin Grafts: “Process of Take”
  16. 16. Skin Graft Take: EpidermisDays Histological changes0–4 Epithelium doubles; crusting, scaling of epidermis; swelling of nuclei & cytoplasm; epithelial cell migration to surface; mitosis of follicular & granular cells3 ++ mitotic activity in SSG not FTSG4–8 Proliferation & thickening of epithelium (up to 7x) desquamationWeek 4 Epidermis returned to normal thickness
  17. 17. Skin Graft Take: EpidermisDay Histochemical changes4 Increased RNA in basal cells, indicating protein synthesis10 RNA returns to normal
  18. 18. Skin Graft Take: Dermis• Fibrous component:Collagen Hyalinized early and progressively replaced with new fibres by 6 weeks; Turned over 3-4X faster than normal skin.Elastin Accounts for resilience; Days 3-7 fragment; Replaced 4-6 weeks.Extracellular Proteins direct the behaviour ofmatrix keratinocytes; Communication between keratinocytes & fibroblasts.
  19. 19. Skin Graft Take: Dermis• Appendages: - sweating dependent on no. of transplanted sweat glands & degree of sympathetic reinnervation; will sweat like recipient site in FTSG only - sebaceous gland activity mostly in thicker grafts: SSG usually dry & shiny - hair grows from FTSG if well taken with no complications
  20. 20. Skin Graft Healing• Initially white then pinkens with new blood supply• Lymphatic drainage by day 6• Collagen replacement from day 7 to week 6• Vascular remodelling for months
  21. 21. Skin Graft Healing• Contraction: - shrinks immediately due to elastic recoil: – FTSG 40%; medium SSG 20%; thin SSG 10%. - secondary contracture as heals: - FTSG remains same size after above shrinkage; - SSG will contract as much as possible; - more dermis = less contraction - ? Due to myofibroblasts
  22. 22. Skin Graft Healing• Reinnervation: – from margins to bed; – 4/52 to 2 years; – Depends on graft thickness and bed; – Uneventful healing leads to near normal 2PD; – Cold sensitivity can be a problem.
  23. 23. Skin Graft Expansion• Based on principle that wounds reepithelialized from the periphery• Expansion provides larger areas from which epithelium can grow• Larger areas can be covered with less skin
  24. 24. Skin Graft Expansion• Meshing - covers large area - easier to contour - fluid can drain through holes - cosmetic results less than ideal - various mesh ratio
  25. 25. Skin Graft Survival• Meticulous technique• Atraumatic graft handling• Well vascularized bed• Haemostasis• Immobilization• No proximal constricting bandages
  26. 26. Skin Graft Failure• Haematoma• Infection• Seroma• Mobility• Inappropriate bed• Dependency• Arterial insufficiency• Venous congestion• Lymphatic stasis• Technical – upside-down