Ch 80 SKin grafts Flashcards
What is the most common donor site for skin grafts?
Cranial lower lateral thoracic area
skin graft
- separated from all vascular and nervous supply
- depends on the reestablishment of vascular supply through engraftment
- full thickness: epidermis and the entire dermis,
- split thickness: epidermis and varying partial thicknesses of the dermis
- island grafts rely mainly on keratinocytes that proliferate and migrate from the edge of the islands to cover the recipient site
- 3 causes of graft failure
SIM
- separation of the graft from the bed
- infection
- movement.
- disrupt the fibrin bonds > impairing revascularization and nutrition of the graft.
- Fluid (e.g., seromas, hematomas, or exudation) mechanically separates the graft from its bed.
- Infection > exudate production but also because bacterial enzymes may cause dissolution of fibrin attachments. - β-Hemolytic streptococci and Pseudomonas spp. produce large amounts of plasmin and proteolytic enzymes
Which grafts lead to the best cosmetic outcome/best hair regrowth?
Full thickness sheet grafts
Unexpanded mesh grafts
By what time must regeneration overtake degeneration for a graft to survive
By day 7-8
post-op bandages
- prevention of postoperative trauma to the graft
- left undisturbed for 24 to 48 hours; this helps to facilitate graft adhesion
- if the graft is not examined until the third to fifth postoperative day, its fate is usually unalterable by that time
- wide mesh nonadherent (petrolatum impregnated) cellulose acetate pad can be placed over the graft and stapled to surrounding healthy skin (to reduce being dislodged)
- 2 to 3 weeks
- engraftment) is well established by 14 days, the process of reinnervation of the graft may take several weeks (may experience paresthesia or dysesthesia)
Where Grafts Will Take
- healthy granulation tissue
- acute wound surface that is vascular enough to produce granulation tissue (after tumor resection) > more rapid vascularization was noted for grafts placed on fresh tissue than on grafts placed on a granulation tissue recipient site
- free from infection and debris
Where Grafts Will Not Take
- stratified squamous epithelial surface
- heavily irradiated tissues
- avascular fat
- chronic poorly vascularized or hypertrophic granulation tissue
- bone, cartilage, tendon
- denuded nerve
- infected wounds, crushed tissues, and chronic ulcers are poor recipient sites for grafting
- not appropriate > manage as open wound or use vascularised APF
Process of Engraftment (Graft Take) - 4 phases
- graft begins to degenerate immediately after being detached
- Regeneration initially progresses more slowly than degeneration; for the graft to survive, regeneration must overtake degeneration by 7-8th day.
- Graft survival depends on early reestablishment of sufficient circulation to provide nutrients and to dispose of metabolic waste products
Adherence
plamatic imbibition
inosculation
vascular ingrowth
What are the 2 phases of graft adherence?
Phase I - Attachment largely dependant on fibrin strands, forming links between collagen and elastin on each surface. Greatest gain over the initial 8 hours (fibrin polymerization results in progressive gain in strength)
Phase II - Begins at approx 72hr. Fibrinous network is invaded by fibroblasts, leucocytes and phagocytes which begin the conversion into a fibrous adhesion. Continues to gain strength until a complete fibrous union is formed at day 10
What is plasmatic imbibition
Nourishment of the graft until it revascularised via dilation of graft vessels, pulling fibrinogen-free, serum-like fluid and cells (erythrocytes and neutrophils) which have accumulated between the graft and recipient bed, into the vessels by capillary action
- Absorbed fluid diffuses into interstitial space cause peak oedema at 48-72hr
- hb breakdown products gives a purplish or cyanotic appearance
Define inosculation
leads to reestablishment of early graft blood flow by connecting the native graft vasculature to the sprouting donor bed vasculature.
- anastomosis of the cut ends of graft vessels with recipient bed vessels of approximately the same diameter
- Most commonly seen between 48-72hr
- anastomoses have an inhibitory effect on capillary bud proliferation in the recipient bed > stops granulation tissue proliferation
- Initially perfusion is slow , normalises by day 5-6
What is vascular ingrowth?
Revascularisation of grafts by the ingrowth of new vessles from the bed into the graft
- Grow at approx 0.5mm/day
- Vessel maturation begins within 48hr
- leads to the stable anchoring
- under cytokine control > VEGF days 5 to 7, corresponding with the peak of vascular ingrowth activity
- lymphatic drainage of the graft by the fourth or fifth day
Describe the expected changed in graft appearance
- Initially pale
- First 48hr, inosculation begins and associated oedema and vasc congestion - red to dark purple
- 72-96hr - lighter reddish hue
- 7-8 days - entire graft red-to-pink if survival is complete
- Day 14 - more normal, pale pink colour
Areas of avascular necrosis are persistently pale
Areas of ischaemic necrosis may appear black
Reinnervation
Reinnervation is better in full-thickness grafts than in split-thickness grafts.
- animals show signs of paresthesia as grafts reinnervate > at least 1 month protection (bandage, ecollar) recommended
- Because the skin of a cat is so thin, split-thickness grafts are not indicated
Graft Bed Preparation
- healthy granulation, epithelium at wound edge is removed
- The top of healthy granulation tissue may be lightly scraped or wiped with a gauze sponge
- The defect is covered with a moist surgical sponge while the graft is harvested, ideally with 0.05% chlorhex (aseptically prepared)
- let natural hemostasis occur before applying the graft
split-thinkness graft harvest
- freehand with a manually operated graft knife or scalpel blade.
- power-driven dermatomes
- 0.35 mm = ideal thickness for partial-thickness grafts in dogs.
- Holes may inadvertently be cut > allow drainage from beneath the graft
- Good donor sites: lateral thorax, the thoracolumbar region, the lateral thigh
Graft Placement
- ensure direction of hair growth same
- graft to overlap the edge of the defect by up to 1 to 2 cm. (overlapped > undergo avascular necrosis, excised later)
- edge secured with sutures or staples
- Additional sutures should be placed in the central field of the graft to ensure good contact with the recipient bed
How long is splinting required after skin graft placement on a limb?
Until the fibrous tissue anchourage is strong enough to withstand shearing strain without capillary rupture (approx 10-14 days)
Negative-Pressure Wound Therapy
paucity of objective data that definitively support its routine use
- In humans > improve the percentage of graft survival and the cosmetic appearance
- Application and maintenance of the portable device was technically straightforward. All dogs receiving portable NPWT after transfer of a free skin graft to the distal extremity had a successful outcome.
List some advantages and disadvantages of split thickness grafts
Advantages
- Better viability than full thickness (89 vs 58% survival)
- Ingrowing vessels have less distance to travel
- Shorter diffusion distance
- Greater explansion
Disadvantages
- Less durable and more subject to trauma
- Absent or sparca hair regrowth
- Scaly appearance due to lack of sebaceous glands
- Expensive equiment
List some benefits of mesh grafts
Drainage
Flexibility
Conformity
Expansion
full-thickness mesh graft harvest
pattern of the wound > sterile paper drape material onto the wound to obtain an imprint in blood
- Cutting the graft 1 cm larger than the pattern and trimming as necessary
What must be done before placement of any full thickness skin graft?
graft prep
Removal of all subcutaneous tissue from graft (defatting)
- scissors or scalpel
- high-pressure hydrosurgical handpiece
exposed dermis will have a cobblestone appearance
How do you create a mesh graft?
Use a #11 blade
parallel rows of staggered incisions
each incision 1-2cm long and spaced 0.5-2cm apart
ALternatively can use a mesh graft explansion unit
What is the recommended explansion ratio for dogs and cats?
3:1 to 4:1
What is the usual cause of superficial infection of a skin graft?
How is it managed?
- Caused by overgrowth of normal skin organisms on abnormal skin
- Gentle cleaning of surface using 0.05% chlorhexidine with topical broad-spectrum ABx ointment
List advantages and disadvantages of mesh grafts
Advantages
- Become pliable and movable
- Resist trauma
- More like normal skin
- Contraction is minimal
- Provide good protection
- No expensive equipment required
Disadvantages
- Do not survive as well as split-thickness grafts in the presence of infection
- Require drainage to survive as well as meshed grafts
List advantages and disadvantages of mesh grafts
Advantages
- Excellent viability (90-100% take)
- Improved drainage
- Improved conformability
- Additional stabilisation as granulation tissue grows into holes which also provded a vascular supply to lateral aspect of mesh holes
DIsadvantages:
- Excess granulation may grow through holes and cover top of graft
Should full central sutures be placed in full thickness non-mesh grafts?
Why?
No - may cause haemorrhage and haematoma formation under a graft with limited drainage
List the advantages and disadvantages of a full thickness un-meshed graft
Advantages
- Become pliable and movable
- Resist trauma
- More like normal skin
- Contraction is minimal
- Provide good protection
- No expensive equipment required
Disadvantages
- Do not survive as well as split-thickness grafts in the presence of infection
- Require drainage to survive as well as meshed grafts
What are the benefits of hyperbaric oxygen therapy in graft healing?
NONE! Contraindicated
- less granulation tissue production
- More inflammation
- Less percentage viability
- Only 13% graft viability at 10 days
- Reduced vascular ingrowth
What support is there for using NPWT in the acute treatment of skin grafts?
Earleir appearance of granulation tissue
More rapid contraction of mesh holes
Earlier adherence
Reduced early graft necrosis at day 10 (1% vs 10%)
> experimental study NPWT against standard bandaging stanley 2013
10 full-thickness grafts applied to 6 feline patients
7 of 10 grafts achieved 100% take, 2 had 95% take, and 1 had 80% take, for an overall average of 97%.
> case series Nolff 2015
most published lack a control group
What sized biopsy punch is used for punch graft harvesting?
5mm - all SQ tissue must be removed
How are pinch and punch grafts placed into the recipient bed?
- Pinch: Small slits made into granulation bed, approx 2-4mm deep and wide and 5-7mm apart, made at 2-=3- degree angle to surface. Each individual graft is tucked deep into a pocket
- Punch - 4mm biopsy punch used to make holes in granulation tissue approx 1-2cm apart in staggered rows. Cotton tipped applicator placed in holes for 5 mins for haemostasis prior to placement of individual punch grafts
List advantages and diadvantages of pinch and punch grafts
Advantages:
- Simple
- No special equipment
- Take quickly and reliably
- Allow drainage
- Withstand infection well
Disadvantages
- Excessive bleeding may float graft out of recipient pocket or delay revascularisation
- Poor cosmetic appearance - sparce hair coat, dry and scaly
- Delicate and prone to injury
What is a stamp graft?
“Chessboard graft”
Split or full thickness graft cut into squared 0.5-2cm and placed onto recipient bed with 1-10mm space between grafts
Paw Pad Grafts
- After grafting, healing via contraction, epithelialization, and hyperplasia forms a durable weight-bearing tissue
- indicated when loss of some digits precludes use of a phalangeal fillet
- large active dogs, pad grafts are less likely to be successful
- Single-Stage Technique
- Two-stage technique involving pad grafts and a bipedicle pouch flap has been described for autografting the pads to a paw stump
What have mucosal grafts been described for? (5)
Replacement of nictitans membrane
Extension of hypoplastic prepuce
Conjunctival replacement
Reconstruction of nasal passage
Urethroplasty
Where are mucosal grafts harvested from?
The buccal or sublingual mucosa (avoiding sublingual salivary duct and sublingual vessels)
resurface reconstructed nasal passages
- recipient area must be prepared for the grafts, granulation tissue initally grow around silicone rubber (Silastic) tubes
- ## approximately 10 days after placing the silicone tubes, a mucosal graft is prepared and placed
Preputial Reconstruction
- Because of their thinness, mucosal grafts revascularize and heal quickly
- as soon as the graft is healed in place, which may be as early as 7 to 10 days, the mucosal-lined preputial tube should be constructed
- Bilateral single-pedicle advancement skin flaps will be advanced to cover the mucosal graft lining.
Alternative to skin graft
- Prpich et al. (2014) described second-intention healing of large wounds in the distal limb following excision of low-grade soft tissue sarcoma in 31 dogs. Twenty-nine (94%) wounds healed completely by second intention, but at a protracted median time of 53 days, with the longest being 179 days. In comparison, seed-grafted wounds in our cohort were recorded to have epithelialised in half the time, at a median of 4 weeks (28 days) after grafting
- Axial pattern flap
Seed skin grafts for reconstruction of distal limb defects in 15 dogs
J. D. Crowley 2020
retrospective
at or below the carpus or tarsus, following trauma (n = 12) or neoplasia excision (n = 3). Complete epithelialisation with minimal contracture was recorded at a median of 4 weeks
Postoperative complications included epidermal inclusion cyst in two dogs. Good functional outcome with acceptable cosmesis despite sparse hair growth was achieved in all cases
Comparison of outcomes for single-session and delayed full-thickness applications of meshed skin grafts
used to close skin defects after excision of tumors on the distal aspects of the limbs in dogs
Bonaventura 2021
- success (>75% graft survival): 27/30 (90%) single-session
18/22 (82%) staged- staged → more bandage changes and longer time to healing (51 days vs 29.5)
- %graft survival, outcome and complication rate not different between groups
recurrence rate > long-term study required?
retrospective
Single, large, meshed full-thickness free skin graft for reconstruction of a dorsal lumbosacral wound defect in a dog
Yasmin Brown 2021
primary healing achieved without post-operative complications
- post-operative management challenging
- tie-over dressing, topical gentamicin, dressing maintained for 23 days
Riggs 2015 – full-thickness grafts for distal limb defects in 20 cats, 32 dogs (58 grafts)
- success (>75% graft survival) – higher for cats: 17/22 (77%) than dogs: 12/32 (38%)
- lower for antebrachium than other areas- complications: overall 50%, cats: 27%, dogs 66%
Or 2017 – NPWT with polyvinyl alcohol foam for full-thickness meshed grafts in 8 dogs
- continuous -125mmHg for 3 days → -75mmHg for 2 days, total 5 days
- firm adherence of grafts by 7 days with granulation tissue filling mesh holes
- excellent graft take initially
- 1/8 partial necrosis due to bandage pressure after removal of NPWT
- PVA foam did not adhere to graft or damage adjacent skin
- PVA foam = hydrophilic, pre-moistened, not requiring interposing layer
Miller 2016 – use of a portable NPWT device for free grafts in 7 dogs (acute grafting on wound)
- PICO → -80mmHg, up to 300ml exudate, max operating time 7 days
- NPWT for 4-7 days, 5/7 dogs discharged from hospital
- 100% graft survival in 7/7
