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 bloodvessels and sweat gland activity) 4. SKIN: Physiology & Function Immunological surveillance Most skin is thin, hair-bearing, has sebaceousglands Skin of palms/soles/flexor surface of digits isthick, 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 & capillaryingrowth Remodelling: Revascularization & fibrousattachment in restoring normal histologicalarchitecture 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 graftvessels 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: EpidermisDays Histological changes04Epithelium doubles; crusting, scaling of epidermis; swelling of nuclei & cytoplasm; epithelial cell migration to surface; mitosis of follicular & granular cells3++ mitotic activity in SSG not FTSG48Proliferation & thickening of epithelium (up to 7x) desquamationWeek 4 Epidermis returned to normal thickness 17. Skin Graft Take: EpidermisDay Histochemical changes4 Increased RNA in basal cells, indicating proteinsynthesis10RNA returns to normal 18. Skin Graft Take: Dermis Fibrous component:CollagenHyalinized early and progressively replacedwith 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 ofmatrixkeratinocytes;Communication between keratinocytes &fibroblasts. 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 bloodsupply 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: FTSG40%; 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 Graft Expansion Based on principle that woundsreepithelialized from the periphery Expansion provides larger areas from whichepithelium can grow Larger areas can be covered with less skin 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. 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