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: Classification
Autografts
 Isografts
 Allografts
 Xenografts

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:
40%; medium SSG 20%; thin SSG 10%.
- secondary contracture as heals:
- FTSG remains same size after above
- SSG will contract as much as possible;
- more dermis = less contraction
- ? Due to myofibroblasts
shrinkage;
– FTSG
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
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Meticulous technique
Atraumatic graft handling
Well vascularized bed
Haemostasis
Immobilization
No proximal constricting bandages
Skin Graft Failure
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Haematoma
Infection
Seroma
Mobility
Inappropriate bed
Dependency
Arterial insufficiency
Venous congestion
Lymphatic stasis
Technical – upside-down