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Physiology of Skin Grafts

Physiology of Skin Grafts. 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). SKIN: Physiology & Function. Dermis:

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Physiology of Skin Grafts

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  1. Physiology of Skin Grafts

  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. 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. 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. SKIN: Anatomy

  6. SKIN: Anatomy

  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. Skin Grafts: SSG

  9. Skin Grafts: Classification • Autografts • Isografts • Allografts • Xenografts

  10. Skin Grafts: “Process of Take” • Vascularity of donor site • Tolerance to ischaemia • Metabolic activity of the graft

  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. 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. 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. 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. Skin Grafts: “Process of Take”

  16. Skin Graft Take: Epidermis

  17. Skin Graft Take: Epidermis

  18. Skin Graft Take: Dermis • Fibrous component:

  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. 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. 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. 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. Skin GraftExpansion • 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. Skin GraftExpansion • Meshing - covers large area - easier to contour - fluid can drain through holes - cosmetic results less than ideal - various mesh ratio

  25. Skin Graft Survival • Meticulous technique • Atraumatic graft handling • Well vascularized bed • Haemostasis • Immobilization • No proximal constricting bandages

  26. Skin Graft Failure • Haematoma • Infection • Seroma • Mobility • Inappropriate bed • Dependency • Arterial insufficiency • Venous congestion • Lymphatic stasis • Technical – upside-down

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