This document discusses the physiology and process of skin grafts. It describes the layers of skin - epidermis and dermis - and their functions. It explains the classification of different types of skin grafts including full thickness and split thickness grafts. The document then outlines the four phases of "take" that a skin graft undergoes as it revascularizes and attaches to the recipient bed. It provides details on the histological and structural changes that occur in both the epidermis and dermis as a graft heals over time. Factors that influence graft survival and potential causes of graft failure are also summarized.

2. Physiology of Skin Grafts

3. 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)

4. 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)

5. 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

6. SKIN: Anatomy

7. SKIN: Anatomy

8. 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

9. Skin Grafts: SSG

11. Skin Grafts: Classification
 Autografts
 Isografts
 Allografts
 Xenografts

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

13. Skin Grafts: “Process of Take”
• 4 Phases:
– Fibrin adhesion
– Plasmatic imbibition
– Revascularization: Inosculation & capillary
ingrowth
– Remodelling: Revascularization & fibrous
attachment in restoring normal histological
architecture

14. 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

15. 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

16. 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)

17. Skin Grafts: “Process of Take”

18. 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

19. Skin Graft Take: Epidermis
Day Histochemical changes
4 Increased RNA in basal cells, indicating protein
synthesis
10 RNA returns to normal

20. 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 of
matrix keratinocytes;
Communication between keratinocytes &
fibroblasts.

21. 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

22. 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

23. 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

24. 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.

25. 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

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

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

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