Skin grafts Flashcards
What is a skin graft?
A segment of epidermis and dermis that is completely removed from the body and transferred to a recipient site.
What are the classifications of free skin grafts based on the donor?
Autograft, allograft, xenograft, isograft
What are the classifications of graft based on thickness?
Full thickness (epidermis and dermis), split thickness (epidermis and part of dermis: thin, intermediate, or thick)
What are some examples of island grafts (or seed grafts)?
Punch, strip, pinch and stamp grafts
What is the most common donor site for graft procurement?
Cranial lower lateral thorax (thin skin which enhances graft survival, but also well haired which improves cosmesis)
What are the benefits/disadvantages of a donor site with a thicker dermis?
Thicker dermis may provide protection to abrasion, but may decrease graft survival initially due to greater distance for diffusion of oxygen and nutrients (lateral neck and dorsal lumbar regions have the thickest dermis)
What are the three most common causes of graft failure?
Movement, infection, separation. These disrupt the fibrin bonds that bind the graft to the bed.
What are some methods to mitigate fluid accumulation under a graft?
Mesh graft and closed suction drainage
Why is infection detrimental to graft survival?
Bacterial products cause dissolution of fibrin attachments (i.e. pseudomonas and hemolytic strep produce plasmin and proteolytic enzymes that disrupt fibrin)
Why is it important to protect a free skin graft beyond the 14 days typically required for vascular ingrowth and engraftement?
Reinnervation of the graft can take several weeks. During this process there can be parasthesia or dysthesia that can result in self-trauma
How long is the immediate post-operative bandage usually left in place following grafting?
24-48 hours
What are two methods to mesh a graft?
Scalpel blade or graft meshing block.
What are two methods to create a split-thickness graft?
Freehand or with a dermatome.
Which types of graft result in the best hair regrowth and cosmetic appearance?
Full thickness sheet grafts or unexpanded mesh grafts
What are the characteristics of an appropriate recipient site for a free skin graft?
Should be vascular and free from infection, i.e. a healthy bed of granulation tissue or an acute wound surface that is vascular enough to provide granulation tissue and is free from infection and debris
What are generally considered poor graft recipient beds?
Fat, chronic/avascular granulation tissue, bone, tendon, cartilage, nerve, epithelium, irradiated surfaces
What are the stages of engraftement (or take)?
- Adherence
- Plasmatic imbibition
- Inosculation
- Vascular ingrowth
- Reinnervation
What are the two phases of graft adherence?
Phase 1: initial links between fibrin strands and collagen and elastin. Causes progressive increase in strength over first 8 hours
Phase 2: begins 72 hours after grafting. The fibrinous network is invaded by fibroblasts, leukocytes and phagocytes. Begins conversion into fibrous adhesion, which is normally complete by day 10.
What is plasmatic imbibition?
The absorption of serum-like fluid and cells from the recipient bed into the graft by capillary action. This provides nourishment to the graft until revascularization can occur.
Hemoglobin breakdown and edema give the graft an engorged and congested appearance. This peaks at 48-72 hours and normally resolves by day 8.
What is inosculation? How does this differ from vascular ingrowth?
Inosculation the anastomosis of graft vessels with recipient bed vessels of approximately the same diameter. Normally noted between 48-72 hours. Successful anastomoses reduce capillary bud formation in the recipient bed, limiting excessive granulation tissue production.
Vascular ingrowth is the ingrowth of new vessels from the recipient bed. Maturation of vessels begins within 48 hours. Under the control of VEGF.
What causes the purplish hue of a free skin graft during the first 48-72 hours after grafting?
Hemoglobin accumulation from plasmatic imbibition
At what rate does new capillary ingrowth occur during the phase of vascular ingrowth of engraftment?
0.5 mm/day
Describe the temporal changes in graft appearance
Initially pale
48 hours: red to dark purple due to congestion and hemoglobin accumulation
72-96 hours: reddish hue
7-8 days: red to pink if the graft has survived
Day 14: normal pale pink colour
What determines graft reinnervation?
Thickness of the graft, amount of scar tissue formation, innervation of the surrounding tissues
Can split thickness grafts be performed in cats?
No because the skin of the cat is so thin
What are some hand knives that can be used to perform split thickness grafting in dogs?
Weck knife (fixed guard), Humby and Watson graft knives (adjustable guard)
What is the most commonly used dermatome?
Brown dermatome
What are ideal mesh expansion ratios for dogs and cats when using a mesh expansion unit?
3:1 to 4:1.
If freehand creation with a scalpel blade should be 1-2 cm long, and 0.5-2 cm apart.
How is drainage achieved in full thickness skin grafts?
A closed suction drain is placed in the wound bed for the first 48-72 hours.
What sort of island graft procedure is depicted?
Strip grafting.
What type of graft is depicted? When is this graft indicated?
Paw pad graft.
Indicated when pad replacement is not possible (loss of digits) or desired using a phalangeal fillet technique.
With paw pad grafting what typically lifts off the graft at around 10-14 days post-operatively?
A hard, darkened stratum corneum. A normal thick covering of pad skin will be restored with time.
Where are mucosal grafts obtained from?
Either buccal or sublingual mucosa
What grafting technique is depicted?
Conjunctival reconstruction using a transposition skin flap and a mucosal graft.
What grafting technique is depicted?
Nasal mucosal replacement using a nasal mucosa graft. Inserted into a granulated, reconstructed nasal passage (normally 10 days after reconstruction). Tubes are typically removed 7 days after grafting.
What are some applications for mucosal grafts?
Nictitans membrane replacement, preputial reconstruction (see image), conjunctival replacement for eyelid repair, line a reconstructed nasal passage, urethral reconstruction.
