skin graftsw
TRANSCRIPT
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:– mechanical strength (collagen & elastin)– Barrier to microbe invasion– Sensation (point, temp, pressure, proprioception)– Thermoregulation (vasomotor activity of blood
vessels and sweat gland activity)
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
SKIN: Anatomy
SKIN: Anatomy
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
Skin Grafts: SSG
Skin Grafts: Skin Grafts: ClassificationClassification
AutograftsIsograftsAllograftsXenografts
Skin Grafts: “Process of Take”
• Vascularity of donor site• Tolerance to ischaemia• Metabolic activity of the graft
Skin Grafts: “Process of Take”
• 4 Phases:– Fibrin adhesion– Plasmatic imbibition– Revascularization: Inosculation & capillary
ingrowth– Remodelling: Revascularization & fibrous
attachment in restoring normal histological architecture
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
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
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)
Skin Grafts: “Process of Take”
Skin Graft Take: Epidermis
Days Histological changes
0 – 4 Epithelium doubles; crusting, scaling of epidermis; swelling of nuclei & cytoplasm; epithelial cell migration to surface; mitosis of follicular & granular cells
3 ++ mitotic activity in SSG not FTSG
4 – 8 Proliferation & thickening of epithelium (up to 7x) desquamation
Week 4 Epidermis returned to normal thickness
Skin Graft Take: Epidermis
Day Histochemical changes
4 Increased RNA in basal cells, indicating protein synthesis
10 RNA returns to normal
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 matrix
Proteins direct the behaviour of keratinocytes;
Communication between keratinocytes & fibroblasts.
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
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
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
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.
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
Skin Graft Expansion
• Meshing- covers large area- easier to contour- fluid can drain through holes- cosmetic results less than ideal - various mesh ratio
Skin Graft Survival
• Meticulous technique• Atraumatic graft handling• Well vascularized bed• Haemostasis• Immobilization• No proximal constricting bandages
Skin Graft Failure
• Haematoma• Infection• Seroma• Mobility• Inappropriate bed• Dependency• Arterial insufficiency• Venous congestion• Lymphatic stasis• Technical – upside-down