Tobias 80, Skin Grafts

Front 1

what is a a skin graft? how is it different from a flap?

Back 1

segment of dermis and epidermis that is completely removed from one site and transferred to another. whereas flaps are living and have blood supply, grafts are essentially dead, and rely on neovascularization to survive

Front 2

classification of skin graft according to their source

Back 2

autograft: same animal
allograft: (homograft) different animal, same species
xenograft: (heterograft) different species
isograft: between identical twins or F1 hybrids

Front 3

cassification of grafts according to thickness

Back 3

full thickness: epidermis and dermis

partial thickness: epidermis and split thickness dermis
further classified as: thin, intermediate,or thick, according to how thick dermal layer is.

Front 4

what are island grafts

Back 4

small pieces of skin implanted in large field
-process of coverage differs from sheet grafts in that islands rely mainly on migration of keratinocytes from the edges of islands

also called seed grafts

they include: pich, punch, strip, and stamp grafts

Front 5

primary indication for grafts i small animals

Back 5

distal limbs where skin tight so no primary closure or local flaps

Front 6

most common donor site in small animals:

Back 6

cranial lower lateral thoracic area

Front 7

3 most common causes of graft failure?

Back 7

1. separation of graft from bed
2.infection: bacterial enzymes and fluid production
3.movement
--disrupts fibrin bond that attaches bed to recip site

Front 8

particular bacteria that damage graft survival? how?

Back 8

B hemolytic strept and Pseudomonas produce large amounts of plasmin and proteolytic enzymes which disrupt fibrin attachments

pseudomonas also has elastase which degrades elastin

Front 9

regarding bandaging, how often should bandages be changed?

Back 9

every 12-24hrs to every 2-4days

immediate post op bandage should be left in place for 1-2days in order to facilitate adherence.
some surgeons leave this inital bandage on for 3-5d--tobias authors DO NOT recommend this

bandage changes at least 2-3 weeks post-op,
after that light bandage for another 2 weeks--because process of rennervation of the graft can take several weeks

Front 10

how long does it take for reenervation of graft? what is significance of this?

Back 10

in rate study sensation started to reurn 14 days post op, not complete until day 40. can have parasthesia so prone to self trauma so must be protected.

Front 11

when do you see hairgrowth, what type of graft has best hair regrowth?

Back 11

2-3 weeks, best with full thickness and unexpanded mesh grafts

Front 12

what are power driven dermatomes?

Back 12

instruments for graft harvest that control depth and can rapidly create uniform split thickness graft

available in electri and nitrogen driven

Front 13

how can grafts be meshed

Back 13

with a blade or a meshing block.
an aluminum block with staggerred parallel rows of cutting blades

Front 14

how are seed grafts obtained?

Back 14

suture needle, skin hook, or forceps to elevate skin, then cut with blade, or skin punch

Front 15

where should grafts be placed
which is better?

Back 15

either healthy granulation tissue bed
OR
acute wound with good blood supply

studies report faster vascularization of grafts on fresh tissue than GT

Front 16

where will graft not take?

Back 16

relatively avascular areas:
-stratified squamous epithelial tissues
-heavily irritated tissues
-avascular fat
-poorly vascularized or hypertrophic GT
-bone
-cartilage
-tendon
-nerve
-excessice/chronic inflammatory process in bed

Front 17

when should graft regeneration surpass degeneration?

Back 17

seventh or eighth day

Front 18

what are the 4 major steps of graft take?

Back 18

adherence
plasmatic imbibition
inosculation
revascularization

Front 19

describe adherence

describe 2 phases

Back 19

soon after placement fibrin strands develop that contract and pull graft to bed

phase 1: attachment depends on fubrn stands which link collagen and elastin. fibrin polymerization results in increased strength. Greatest gain 8 hours post grafting.

phase 2: begins at 72hrs. fibrinous network invaded by fibroblasts, WBCs, conversion to fibrous adhesion starts. continues until complete fibrous union by day 10.
maturation results in contraction of graft

Front 20

is contraction more in thin or thick grafts?

Back 20

thin split thickness

Front 21

what is plasmatic imbibition, timeframe?

Back 21

graft vessels spasm and constrict when harvested. fluid builds up between graft and bed as bed vessels leak. soon after placement in bed, graft vessels dilate, pulling fibrinogen-free serum and cells into graft via capillary action. this continues until graft is revascularized.

accumulation of Hb and breakdown products gives graft a cyanotic apearance

absorbed fluid diffuses into interstitium of graft, produces edema.
this peaks 48-72 hours post grafting

vascular connection is established about this time, but venous drainage lags behind, so edema may increase

graft returns to normal weight by 8th day post-op as lymphatics and veins improve.

Front 22

what is inosculation

Back 22

the anastomosis of the cut ends of graft vessels with recient bed vessels of about same diameter.

can begin around 24 hours post, more commonly noted between 48-72 hours

capillary buds for along fibrin network

many make anastamoses but few survive

connections can be initiated either way (graft to bed, bed to graft)

anastamoses inhibits new capillary bud formation in bed. if separation of graft from bed occurs, this inhibition does not occur, and GT formation in bed continues

initally flow is slow when blood begins to flow into the graft on day 3 or 4 post grafting, but resumes normal velocity by day 6

Front 23

diagram of engrafting

Back 23

Front 24

describe the process of vascular ingrowth. which direction? rate?

Back 24

grow from bed to graft

new capillary ingrowth at rate of 0.5mm/day

initaially tortuous, then become arterioles

VEGF most elevated 5-7d, peak ingrowth

new lymphatics start day 4-5

Front 25

describe the color changes and timeframe as grafts take

Back 25

initially pale
first 2-3 days: purple/red as inosculation begins
light red by 72-96
by day 7-8 entire graft is pink or red if took

Front 26

what happens if ontly partial thickness survives

Back 26

if partial thikness take, may be darkly discolored becuse of ischemic necrosis of epidermis ,but vascularization of dermis. after epidermis sloughs or is debrided, dermis will re-epithelialize.

final appearance is sparsely haired epithelialized skin

Front 27

is reenervation better in partial or full thickness grafts?

Back 27

better in full thickness

Front 28

can you use split thickness grafts in cats?

Back 28

not really because skin is so thin

Front 29

how do you prepare wound bed for grafting?

Back 29

chronic GT completely excised, replaced by acute healthy GT bed (day 4-5)

epithelium at wound edge is removed

top of healthy GT bed can be scraped OR 0.5-2mm off top can be sharply excised

defect covered with chlorohex soaked gause while graft developed

let natural hemostasis occur in bed

Front 30

weck knife

Back 30

goulian type uses disposable blade and has guard that slides over blade to fix depth

humby and watson are other types of knives

razor blade can be used.

Front 31

what is good depth for split thickness graft

Back 31

0.35mm thick (same thickness as scalpel blade)

Front 32

when harvesting graft, how can you prepare donor site?

Back 32

SQ saline to tent skin

Front 33

name 4 good donor sites for grafts

Back 33

lateral thorax
thoracolumbar region
proximolateral forelimb
lateral thigh

Front 34

how is the graft placed?

Back 34

1. so that direction of hairgrowth will be same as surrounding tissues
2.graft may be cut to exact fit, but many surgeons like it to overlap the edges of wound bed by 1-2 cm. the overlapped portion will necrose and can be excised later
3. edges should be secured with sutures through graft in underlying skin
4. additional sutures in center to assure good adherence

Front 35

what can you do about hematomas under the graft

Back 35

can be removed with q-tip under graft

thrombin or saline soaked solt to irrigate underneath graft before putitng on bandage

after surgery (days) hematoma can be reomved by making an incision in the graft and milking it out, or q tip

Front 36

brown dermatome

Back 36

Front 37

for how long are immobilization splints usually necessary in limbs?

Back 37

2 weeks

Front 38

negative pressure wound therapy?

Back 38

studies of split thickness grafts in people have shown improved percent graft survival compared with tie overs

Front 39

name 2 main advantages of split thickness grafts, describe why

Back 39

1.better viability
-study noted 89% survival vs. 58% for full thickness grafts on dog forelimbs
-greater capillary density
-less distance for for capillaries to traverse
-shorter distance for diffusion, better plasmatic imbibition

2.less wound contraction
-may be better if contraction would be big problem
-there is actually expansion of the graft

Front 40

what are some disadvantages of split thickness grafts?

Back 40

1.less durable

2. sparse hair growth

3. scaly appearance, may lack sebaceous glands

4.may require more specialized equipment

Front 41

what are 4 advantages of full thickness mesh graft?

Back 41

drainage
conformity
flexibility
expansion

Front 42

what are 3 indications for mesh grafts?

Back 42

1.allow drainage from a wound with minor exudate/bleeding
2.cover large skin defects when insufficient donor skin
3.reconstruct irregular surfaces

Front 43

preparing the mesh graft

Back 43

after harvesting the skin from donor site (using template for measurements)
place on cardboard sq side up, stretched with hypodermic needles
sq tissue must be removed-"defatting"
meshing done with #11 blade
incisions 1-2cm long, 0.5-2cm apart

Front 44

mesh expansion unit

Back 44

aluminum block with stainless steel blades, graft placed on block and rolled with teflon or nylon roller

expansion occurs in only one directon depending on orientation of blades.

Front 45

best expansion ratio

Back 45

3:1 or 4:1 for dogs and cats

Front 46

is hyperbaric O2 therapy good for mesh grafts?

Back 46

horse study: trend towards less granulation tissue and less edema, but more inflammation and less viability-

dogs study:
-13% viable at 10d post grafting with O2
-concurrent admin of deferoxamine (O2 radical scavenger) improved survival to 65%

still way less than expected

some conflicting results i rats and pigs

currently hyperbaric O2 contraindicated as adjunct therapy for grafts

Front 47

what are some advantages of mesh grafts, diasadvantages?

Back 47

-excellent viability: 90-100% take when well cared for

-improved drainage

-conformability

-full thickness associated benefits

-disadvantage: excess gt can grow through the slips and up over the graft

Front 48

what are the indications for full thickness unmeshed craft

Back 48

where postgraft contraction might result in contracture (like distal limbs, joint surfaces)

small to moderate sized wounds

wounds with minimal expected drainage/exudate

Front 49

drainage with full thickness grafts?

Back 49

yes--small closed suction drains
--use butterfly needle to create drain

--can also do stab incisions, but they tend to clot

Front 50

what is the diff between pinch and punch grafts

Back 50

pinch: small pieces of skin cut free

punch: small pieces of skin cut with a punch biopsy

Front 51

indications for pinch/punch grafts

Back 51

small limb wounds
contamnated wounds
low grade infected wounds
areas that dont need major durability
irregular contour

Front 52

technique for punches

Back 52

insert 5mm punch at angle of hair follicles

Front 53

placement of pinch grafts--preparation of recipient bed

Back 53

small slits are made in recipient bed, almost parallel to surface of the wound, openings upward
pockets are 2-4mm deep and 5-7mm apart
apply direct digital pressure to keep it in its pocket

Front 54

placement of punch grafts

Back 54

cylindrical holes 1-2cm apart
4mm punch used to make the holes. q-tip placed in holes for 5 minutes before graft placement for hemostasis

Front 55

outcome pinch grafts

Back 55

thin epithelium, scaly, sparly haired, prone to injury
but take well

Front 56

what are strip grafts

Back 56

5mm wide strips placed in parallel grooves cut in a GT bed. wounds that are parallel to long access on limb are good for these

Front 57

what are stamp grafts?

Back 57

chessboard grafs.
square patches-05-2cm per side
no particular indication

disadvantages are that may need to cut depressions into GT to keep the grafts from moving or being disturbed by the bandage, and these may bleed alot because of size of grafts.

Front 58

what are paw pad grafts?

Back 58

small segements of full thickness pad tissue --placed into areas of GT that have formed in an absent metatarsal or metacarpal pad.
after grafter, healing via contraction, epithelialization, and hyperplasia forms a durable weight bearing tissue.

indicated when phalangeal fillet wont work

tough in large breed active dogs
grafts are taken as rectangles from other paw pads, and secured into GT bed by 4-0 suture on the corners

Front 59

paw pad grafts, aftercare

Back 59

donute to take pressure off pad, two mason metasplints incorporated over cast padding

Front 60

what is the two stage technique for pad grafting?

Back 60

-option when paw has sustained severe damage requiring amputation of digits at metacarpaophalangeal joint.

Step 1: pad grafts are harvested and implanted in the lateral thoracic area-each graft is sutured to cutaneous trunci mm. bandaged for 7 days,

Step 2: bipedicle pouch flap containing grafts is elevated and animals paw is wrapped in flap

the advantage of this technique is that SQ layer of graft can replace the fibroelastic pad tissue.

Front 61

what types of mucosal grafts have been described in small animal medicine

Back 61

nicititans,
hypoplastic prepuce,
conjunctival replacement
nasal passage
urethroplasty

Front 62

where can mucosal grafts be placed?

Back 62

GT bed,
acute wound bed
dermal side of freshly raised transposition flap?

Front 63

how would you prepare nasal passages for grafting?

Back 63

place silicone stents to encourage tubular formation of GT

Front 64

where are mucosal grafts harvested from?

Back 64

buccal or sublingual mucosa

Front 65

how do you do a conjunctival replacement

Back 65

graft sutured to dermal side of transpoition flap that will be used to reconstruct eyelid. then flap returned to its original position for 4-7 days, then eslevated, transposed, and sutured into defect

Front 66

how do you do a nasal mucosa replacement?

Back 66

10 days after silicone tubes are placed, they are removed.

mucosal grafts are sutured with submucosal side out!! around the tubes, with traction sutures placed.

tube is inserted, and graft and tube are sutured into place. sutures are placed through skin and graft to create new mucocutaneous junction at rostral end. tube acts as stent--removed at 7 days.

Front 67

nasal mucosa reconstruction

Back 67

Front 68

conjuntival reconstruction

Back 68

Front 69

advantages and disadvantages of mucosal grafts

Back 69

thin, easily vascularized, heal quickly

shrink alot, can shrivel, very delicates, difficult to handle

Front 70

preputial graft

Back 70

A mucosal graft was previously applied to a wound bed that was created by removing abdominal skin at the cranial aspect of a hypoplastic prepuce. The penis protrudes from the prepuce. After the graft has healed, the lateral and cranial edges of the mucosal graft are incised (A), and the graft is undermined to mobilize it (B). The dissection plane is kept deep to preserve the blood supply. C, The lateral edges of the graft are being sutured together around the penis to form a lining for the preputial extension. D, Completed suturing of the mucosal graft lining. Bilateral single-pedicle advancement skin flaps will be advanced to cover the mucosal graft lining. E, Skin flaps sutured together over the mucosal lining.