Chapter 80 Skin Grafts

Question 1

Based on graft source, what are the 4 classes of graft?

Answer 1

• Autograft
• Allograft
• Xenograft
• Isogaft (twin or F1 hybrid)

Question 2

In experimental beagle study, how did skin on dorsum differ from elsewehere

Answer 2

Thicker dermal and overall thickness, greater density of hair follicles

Question 3

What are the three most common causes of graft failure?

Answer 3

• Infection
• Movement
• Separation

–> disruption of fibrin bonds.

Question 4

Which two bacteria types specifically produce large amounts of plasmin and proteolytic enzymes?

Answer 4

Pseudomonas and b-haemolytic Strep

Question 5

When is first graft dressing change recommended?

Answer 5

48 hours

Question 6

In rats, when was graft innervation first noted and when complete?

Answer 6

Noted day 13

Complete by day 40

Question 7

List an instument that can be used for split thickness graft harvest

Answer 7

Dermatome,

most commonly used is called ‘Brown dermatome’

Question 8

What exam finding can be used as a sign that granulation tissue bed is likely healthy for graft?

Answer 8

Advancement of epithelium from wound edge.

Question 9

List the 5 stages of graft take = ‘engraftment’. Highlight the three key phases

Answer 9

1. Adherence:
   
   • Phase 1 up to 72h = fibrin attachments.
   • Phase 2 fibrin network invaded by fibroblasts etc: Fibrin –> fibrous network
2. Plasmatic imbibition:
   
   • ​​serum like fluid absorbed by capillary action –> oedematous appearance. Venous drainage may lag behind arterial. Peaks day 2-3
3. Inosculation:
   
   • Anastomosed between capillary bed and graft vessels. Day 3-4.
4. Revascularization:
   
   • ​​New vessel ingrowth, 0.5 mm/day
5. Reinnervation:
   
   • takes up to 40d to be complete in rats

Question 10

Outline the change in healty graft appearance over time

Answer 10

Day 1-3: Congested, oedematous. Breakdown products of Hb

Day 3-4: Becoming reddish

By day 7-8: Graft pink/red if surviving

By day 14: More normal pale pink

Question 11

Comment on split thickness grafts and cats

Answer 11

Split thickness not indicated in cats as skin is so thin

Question 12

What is the recommended thickness of split thickness grafts?

Answer 12

0.38mm (n.b. scalpel blade thickness is 0.35mm)

Question 13

What is the advantage of split thickness grafts and 3 proposed mechanisms behind that

List 3 disadvantages

Answer 13

Thinner so better viability (one study reported 89% survival vs 58% for full thickness.

Proposed mechanisms are:

• Greater density of vessels in dermal plexus (compared with subdermal plexus of full thickness grafts).
• Shorter distance for vascular ingrowth
• Shorter distance for diffusion

Disadvantaged:

• Thinner dermis
• Sparse hairgrowth
• Expensive equipment

Question 14

List 3 indications for mesh grafts

Answer 14

1. Allow drainage of fluid
2. Cover large defects
3. Reconstruct irregular surfaces

Question 15

What is the appearance of full thickness graft when sc tissue adequately timmed?

Answer 15

Cobblestone

Question 16

Comment re hyperbaric oxygen + grafts

Answer 16

Contraindicated

Question 17

List 3 advantaged of meshed graft

Answer 17

1. Allows drainage
2. Improves conformability
3. Can be affixed centrally through mesh holes
4. Granulation tissue in holes can help adhere graft (although excess may grow through)

Question 18

What is the main attribute of a full thickness, unmeshed graft?

Answer 18

Minimal wound contraction and graft area increases after healing

Consider drain or few stab incisions (but may bleed!)

Question 19

List 3 indications for pinch/punch grafts

Answer 19

• Granulating wounds
• Small wounds on limbs
• Contaminated/low grade infection wounds
• Wounds with irregular contour
• When placement beneath wound surface will protect them from rubbing

Question 20

How does pinch vs punch graft placement vary?

Answer 20

Pinch placed into pockets of granualtion tissue at 20-30 degrees. Usually reserved for shallow granualtion beds

Punch grafts sunk perpendicularly into tissue

Question 21

List 5 advantages of pinch/punch grafts

List 2 disadvantages

Answer 21

Advantages

• No special equipment
• Good take as high volume granulation tissue: graft area
• Easy donor site closure
• Allow drainage
• Good for irregular surfaces

Disadvantages

• Poor cosmetic appearance
• Blood from granulation tissue wund may ‘float’ graft out of pocket

Question 22

When are pad grafts indicated?

Answer 22

When phalageal fillet not possible

Question 23

Lost two methods of pad graft

Answer 23

• Single stage technique: Segmental grafting
• Two-stage technique i.e Pad grafts sutures to cutaneous trunci of flank and allowed to heal (7d). Then distant direct bipedicle flap performed (also provides thick subdermal fatty layer)

Question 24

List 3 examples where mucosal graft has been used

Answer 24

• Nasal passages
• Conjuntiva
• Nictitans membrane
• Prepuce
• Urethroplasty

Question 25

What are the two usual sites of mucosal graft harvest?

Answer 25

Buccal or sublingual mucosa (can inject 0.01% epinephrine beneath mucosa to minimise bleeding)

Question 26

How is mucosal graft for conjunctival replacement performed?

Answer 26

Free mucosal graft harvested and attached to cut side of proposed flap. Flap *left in situ* for 4-7d, then elevated and transposed

Question 27

Briefly outline how mucosal graft for reconstruction of nasal passages is perormed

Answer 27

* Silicone stents sutured into nasal passages for 10d to allow granulation tissue to form. * Silicone stents removed, mucosal graft sutured as tubes around stents (cut side facing outward). Stay sutures rostrally and caudally (caudal ones fed through tube so that also exiting rostrally. * Stents slid back into place with graft held taught around stent. * 3 Mucosa-skin sutures rostrally and 3 stent, mucosa, skin sutures to hold everythingin place. Stay stures cut.

Question 28

Describe a point of note when performing mucosal graft as a flat sheet e.g. for prepucial recon:

Answer 28

Contraction as they heal i.e. second stage of surgery performed as soon as graft taken to bed (approx 7d as very thin!) 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.

Question 29

What did Riggs et al (JAVMA, 2015) define as success for free skin grafts on limbs? What was success rate in dogs? And in cats?

Answer 29

\>75% graft take Dogs 38% success Cats 77% success