Skin Grafts PDF

C H AP T E R 8 0 Skin Grafts Mark W. Bohling, Steven F. Swaim General Considerations A skin graft is a segment of epidermis and dermis that is completely removed from the body and transferred to a recipient site. The alternate term free graft is sometimes used to help distinguish skin grafts from...

C H AP T E R 8 0 Skin Grafts Mark W. Bohling, Steven F. Swaim General Considerations A skin graft is a segment of epidermis and dermis that is completely removed from the body and transferred to a recipient site. The alternate term free graft is sometimes used to help distinguish skin grafts from skin flaps, which are sometimes referred to as flap grafts. Skin flaps are living, vascularized tissue at the time of implantation; this is in contrast to skin grafts, which are separated from all vascular and nervous supply when implanted—essentially a dead piece of skin. Skin graft survival at the recipient site depends on the reestablishment of vascular supply through engraftment or “take”—the process in which a dead piece of skin comes back to life. Classification Skin grafts can be classified according to their source as follows: (1) autografts (autogenous grafts), in which the donor and recipient sites are on the same animal; (2) allografts (homografts)—in this case the donor and recipient sites are on genetically different individuals of the same species; (3) xenografts (heterografts) in which the donor and recipient sites are on animals of different species; and (4) isografts, a graft between identical twins or between F1 hybrids produced by crossing inbred strains.17,75 Although human medicine makes extensive use of all types of grafts, in veterinary medicine, almost all grafts are autografts; therefore in this chapter we will restrict the discussion to autografts. Grafts are also classified according to thickness and may consist of either the full thickness of the skin, which is composed of epidermis and the entire dermis, or a split thickness of skin, which is composed of epidermis and varying partial thicknesses of the dermis. Split-thickness grafts have been further classified as thin, intermediate thickness, or thick, according to the thickness of the layer of dermis included in the graft.12,17,57 Island grafts are so named because they consist of small pieces of skin that are implanted into a large field of open granulation tissue. The process of coverage of the wound differs fundamentally from sheet grafts in this important respect—island grafts rely mainly on keratinocytes that proliferate and migrate from the edge of the islands to cover the recipient site (hence their alternate name, seed grafts). Island grafts include pinch, punch, strip, and stamp grafts. Indications and Preoperative Considerations Skin grafts are indicated when there has been major loss of skin from trauma or other factors, such as tumor removal. In dogs and cats, skin grafting is primarily indicated for loss of skin on the distal limbs, where the paucity of loose skin precludes wound closure via skin mobilization or construction of local flaps.28,74,75 Skin grafts are also occasionally used to resurface large wounds of the trunk, such as may be seen with large full-thickness burns. General and local conditions are considered before grafting is performed. Debilitated patients and those with chronic disease may have comorbidities that put them at higher risk for graft failure. These conditions may include cachexia, anorexia or hyporexia, chronic inflammatory conditions, uremia, hypoperfusion, and infections, to name a few. Obvious deficiencies such as anemia with low hemoglobin concentration should be corrected before grafting.75 The graft recipient site should be healthy, free from infection, and well perfused, and the donor skin should match the recipient area as closely as possible with regard to thickness, color, and haircoat.12 The Graft Donor Site To produce the optimum cosmetic outcome, the ideal graft donor site should have hair of the same color, texture, length, and thickness as the hair surrounding the recipient site. Additional considerations may also come into play when selecting a donor site. These include access for graft harvest without repositioning the patient for graft placement and closure of the donor site—both for ease of closure and for minimum potential for postclosure morbidity or complications. In addition, the thickness of donor skin may also be a factor: thicker skin with thicker dermis may help to provide a greater degree of protection from normal abrasion. In a histomorphometric study of canine cadaver skin from healthy young adult beagles,4 skin samples from the lateral neck and dorsal lumbar regions were significantly greater in dermal thickness and total thickness compared to samples from the lateral regions of the thorax, shoulder, or abdomen. Increasing haircoat density may similarly help to confer protection. In the same study the dorsal lumbar region was also found to have the greatest density of hair follicles, both before and after the graft was prepared for placement. One negative aspect of thicker donor skin is the greater distance for diffusion of oxygen and nutrients during the early postgrafting stages, with a potential for negative impact on graft survival, so this must also be taken into consideration. Historically the most common donor site selected has been the cranial lower lateral thoracic area.73 The skin is fairly thin, thus benefiting graft take, yet it is still well haired, offering good cosmetic results. In addition, because of the abundance of loose skin in this area, the donor site can be easily closed after the graft is harvested and typically heals with minimum morbidity. Common Causes of Graft Failure The three most common causes of graft failure are separation of the graft from the bed, infection, and movement. These disrupt the fibrin bonds that bind the graft to the bed, thus impairing revascularization and nutrition of the graft. Fluid accumulation beneath the graft (e.g., seromas, hematomas, or exudation) mechanically separates the graft from its bed. Mesh grafts and closed-suction drainage are the best ways to facilitate drainage of such fluid accumulations. Infection is detrimental to graft survival not only because of 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 disrupt the fibrin attachments of the graft to the recipient bed. Pseudomonas spp. also degrade elastin through the production of elastase; elastin facilitates graft adhesion through its adherence to fibrin.46,73 Postoperative Considerations Bandages Although the general surgical techniques for skin grafting in humans can also be applied to dogs and cats, postoperative care in veterinary graft patients differs markedly from that in human graft patients because, unlike in human patients, prevention of postoperative trauma to the graft is a major problem in veterinary patients. Therefore the graft must be protected at all times by the maintenance of effective bandaging and by the use of appropriate patient restraint techniques to prevent self-trauma to the bandage and graft beneath. Bandaging and splinting methods vary with the type and location of graft; specific bandaging information in this chapter is described with each type of graft. The bandage change interval may vary from once daily to once every 2 to 4 days, depending on the type of graft and the wound. The immediate postoperative bandage is usually left undisturbed for 24 to 48 hours; this helps to facilitate graft adhesion, immobilization, and absorption of wound fluid and protect the graft from trauma. Some surgeons prefer to leave the initial bandage in place for 3 to 5 days.45 However, the authors are of the opinion that the bandage should be changed sooner (24 to 48 hours) because there are instances in which a skin graft may encounter early postoperative problems that would interfere with successful engraftment. If these problems are identified and corrected, a good take is still possible; however, if the graft is not examined until the third to fifth postoperative day, its fate is usually unalterable by that time. One reason given for delaying the initial postoperative bandage change is concern about the graft adhering to the contact layer, thus being dislodged from the recipient bed. Warm saline can be applied to soften dried wound fluid and the contact layer to facilitate its removal and prevent the problem of bandage adherence to the graft.45 Alternatively, a wide mesh nonadherent (petrolatum impregnated) cellulose acetate pad can be placed over the graft and stapled to surrounding healthy skin before placement of an overlying absorptive bandage. This dressing can be left in place during subsequent bandage changes. Whatever bandage change interval is selected, regular bandage changes should be performed for at least 2 to 3 weeks postoperatively. After that time a light bandage for an additional 10 to 14 days is highly recommended.46 Even though vascular ingrowth (and thus engraftment) is well established by 14 days, the process of reinnervation of the graft may take several weeks. When sensory testing was performed on skin grafts applied to the backs of rats, return of sensation was first noted on the thirteenth postoperative day at the graft margins; however, complete reinnervation required 40 days.83 During the period of reinnervation, human patients may experience paresthesia or dysesthesia. It is reasonable to assume that animals may also experience similar sensations, leading to self-trauma. Therefore, during the entire period of bandaging, appropriate methods should be used to prevent the patient from traumatizing the bandage and the underlying graft. Besides the prevention of self-trauma, another important function of postoperative bandaging is immobilization of the grafted area. During the first few days after grafting, excessive motion of the graft site may disrupt the adherence of the graft from the recipient bed, potentially leading to subgraft seroma formation and failure. Even after adherence, excess motion may still lead to graft failure by shearing off the capillary buds as they grow into the graft. Immobilization of the grafted part can be accomplished by means of bulky bandages, slings, splints, and casts. Schroeder-Thomas splints or spica splints may be useful on the upper portions of the limbs; spica splints are especially useful on the upper extremities of cats.45 Bandages have potential adverse effects. Uneven application of tension during bandaging, wrinkles or creases, or excessive buildup of bandage material may cause excessive pressure on the graft, leading to necrosis. Improper immobilization may result in a bandage's abrading the graft.46 A wet bandage permits wicking of bacteria to the graft, which can lead to infection, and may result in maceration of surrounding skin. Cosmesis Noticeable hair regrowth on a graft is usually seen 2 to 3 weeks after grafting. It may vary from a full regrowth to sparse regrowth. Sparse regrowth may be caused by damage to hair follicle bases during removal of subcutaneous tissue or poor graft revascularization. In general, hair regrowth on split- thickness grafts and on strip, punch, and expanded mesh grafts is patchy. Full-thickness sheet grafts and unexpanded mesh grafts result in the best hair regrowth and cosmetic appearance.23 Surgical Principles Instrumentation Full-thickness unmeshed grafts, full-thickness mesh grafts, seed grafts, strip grafts, and stamp grafts can be performed with basic surgical instruments. Some split-thickness grafts and split-thickness mesh grafts require special instruments. Split-thickness skin grafts can be harvested freehand with various types of freehand knives or blades. The knives have depth control adjustments to help regulate the thickness of skin that is cut. However, practice and experience are necessary to use these instruments effectively.74,75 A #10 scalpel blade can be used to cut a split-thickness graft, although the process is time consuming29; also, depth control is difficult, and holes may be inadvertently cut in the graft.57 Power-driven dermatomes incorporate depth control and are capable of rapidly harvesting a uniform split-thickness graft. They are also generally easier to use than manually operated knives. An electric dermatome has been described for cutting split-thickness grafts in veterinary surgery.11 A nitrogen-powered dermatome of the same design is also available. Grafts can be meshed with a scalpel blade or a graft meshing block. A graft meshing block consists of an aluminum block that contains numerous staggered parallel rows of notched cutting blades. The graft that is to be meshed is placed on this block with the epithelial surface facing up. Then a Teflon or nylon roller is rolled over the graft while pressing down firmly. This pushes the skin down onto the knives, creating numerous slits in the skin, thereby producing a meshed graft.22,72 Seed grafts can be harvested by using a suture needle, skin hook, or forceps to elevate the skin before cutting it with a scalpel blade. A disposable Keyes dermal biopsy punch may be used to harvest punch grafts. Disposable skin stapling devices provide a rapid, effective means of closing donor site incisions and affixing graft edges to the recipient site.74 The Graft Recipient Site Where Grafts Will Take Successful skin engraftment, or take, depends on establishment of arterial and venous connections with the recipient bed.47 The graft bed must be capable of furnishing adequate vasculature for the graft. Grafts should be placed on either healthy granulation tissue or an acute wound surface that is vascular enough to produce granulation tissue and is free from infection and debris (e.g., exposed muscle). If epithelium is advancing from the wound edge over healthy granulation tissue, the wound should be able to support a skin graft.51,57 An adequate granulation tissue bed that will support engraftment may come from either a surgically created acute wound or an acute natural wound that has been rendered surgically clean.36,54 A slightly contaminated wound that is being treated before the establishment of bacterial colonization may be cleaned, irrigated thoroughly, and debrided before acute application of a skin graft during the same procedure.75 In this situation, provision must be made for a greater amount of bleeding and production of wound fluid, compared with a granulation tissue recipient bed, and extra absorptive capacity should be built into the bandage. An alternative to acute grafting of an open wound is to debride the wound thoroughly, bandage with daily dressing changes, and apply a graft on the third postoperative day.10 The wound must be visually free from evidence of infection; additional provision for drainage from beneath the graft is indicated if there is any doubt about the condition of the tissues.74 Clean abrasion and avulsion wounds may be grafted acutely.57 Successful acute grafting has also been reported in a case series of seven canine patients following tumor resection on the antebrachium (six cases) or tarsometatarsus (one case).78 In this case series the overlying antebrachial fascia was resected as the deep margin for antebrachial tumor resection in five cases, with the underlying muscle serving as the recipient bed. One antebrachial tumor required a deeper margin for complete excision, and in this patient and in the patient with a tarsometatarsal mass, the grafts were applied directly to the underlying tendons; both grafts survived with a good to excellent final cosmetic result. One possible explanation of the good results achieved in spite of apparently suboptimal recipient sites could be an improved rate of neovascularization associated with acute phase healing—in other studies of skin grafting on dogs, more rapid vascularization was noted for grafts placed on fresh tissue than on grafts placed on a granulation tissue recipient site.3,28 Where Grafts Will Not Take Engraftment requires vascular ingrowth; therefore grafts will not take when applied to any tissue lacking adequate vascularity of the recipient surface that will be in contact with the raw (deep) surface of the graft. Examples of such surfaces include stratified squamous epithelial surfaces21; heavily irradiated tissues; avascular fat; chronic poorly vascularized or hypertrophic granulation tissue; or bone, cartilage, tendon (with certain exceptions—see previous paragraph), or nerve that has been denuded of overlying connective tissue.10,11 Successful engraftment is also prevented by an excessively intense or chronic inflammatory process at the graft bed; therefore infected wounds, crushed tissues, and chronic ulcers are poor recipient sites for grafting.2 Wounds that lack sufficient vascularity to support a graft (e.g., wounds with tissue denuded of its connective tissue covering, irradiated tissue, and avascular fat) should be reconstructed with vascular flaps rather than grafts. If an unhealthy graft recipient surface is present (e.g., infected tissue, crushed tissue, hypertrophic granulation tissue, chronic granulation tissue, or chronic ulcers), the wound should be debrided, irrigated, and properly bandaged to promote the development of healthy granulation tissue on which to place the graft.51,73 The Process of Engraftment (Graft Take) General Factors The newly harvested skin graft begins to degenerate immediately after being detached from the donor site; regeneration cannot begin until after the graft begins to receive nourishment from the recipient bed. Regeneration initially progresses more slowly than degeneration; for the graft to survive, regeneration must overtake degeneration by the seventh to eighth postoperative day.18,53 Graft survival depends on early reestablishment of sufficient circulation to provide nutrients and to dispose of metabolic waste products.18,22,41,53 Adherence Shortly after placement, adherence between the graft and recipient bed is established via a network of fibrin strands that contract to pull the graft into closer apposition with the bed. The process of graft adherence has been divided into two functional phases. In phase I of graft adherence, attachment is largely dependent on the aforementioned fibrin strands, which form links between collagen and elastin on the exposed graft surface and collagen and elastin on the surface of the recipient bed. During phase I, fibrin polymerization causes the attachment between the graft and recipient bed to undergo progressive gain in strength, with the greatest gain occurring during the initial 8 hours after graft placement. Phase II of adherence begins at approximately 72 hours after grafting, when the fibrinous network is invaded by fibroblasts, leukocytes, and phagocytes; these begin the conversion into a fibrous adhesion. Gain in strength continues with conversion of the fibrin network to fibrous tissue until a complete fibrous union is present by postoperative day 10.21,53,74,75,77 Even after healing, collagen maturation continues between the graft and bed. This maturation is responsible for any graft contraction that occurs; contraction is more marked in thin split-thickness grafts than in thick split-thickness grafts.17 Plasmatic Imbibition After the graft is harvested, its blood vessels vasospasm, thus expelling most of the blood from the severed ends.6,14,27,53,58 Serum, erythrocytes, and neutrophils accumulate between the graft and recipient bed as a result of vascular leakage from the recipient bed vessels.14,18,21 Soon after placement in the recipient site, graft vessels dilate,6 pulling fibrinogen-free, serum-like fluid and cells into the graft by capillary action. This process continues, pulling cells and serum into the dilated graft vessels (Figure 80.1A), keeping them dilated and nourishing the graft until it revascularizes. Accumulation of hemoglobin and its breakdown products gives a purplish or cyanotic appearance to the graft. Absorbed fluid diffuses into the interstitial space of the graft, producing edema; this peaks at approximately 48 to 72 hours after grafting. Vascular connection between the graft and recipient bed is established at about that time; however, venous drainage may lag behind arteriolar inflow; therefore edema may increase initially.5,6,16 As time passes, venous and lymphatic drainage improve, and excess fluid is able to exit the graft, resulting in a regression of edema, and the graft returns to a normal weight by the eighth postgrafting day.5,13,14  FIGURE 80.1 Physiology of avascular engraftment. During the early stages of graft tissue transfer, nutrient exchange necessary for graft survival is primarily driven by plasmatic imbibition (A). Inosculation (B) leads to reestablishment of early graft blood flow by connecting the native graft vasculature to the sprouting donor bed vasculature. Engraftment culminates with revascularization (C), which is the process of vascular ingrowth, extracellular matrix deposition, and maturation that leads to the stable anchoring of the transplanted tissue. (From Eisele DM, Smith RV: Complications in head and neck surgery, ed 2, St Louis, 2009, Mosby/Elsevier.) Inosculation Inosculation is the anastomosis of the cut ends of graft vessels with recipient bed vessels of approximately the same diameter (see Figure 80.1B). This process may begin as early as 22 hours after graft placement,14,18 but it is more commonly noted between 48 and 72 hours.5,15,45,80 The fibrin network holding the graft on the bed serves as scaffolding along which capillary buds from the graft bed grow and meet the severed ends of graft vessels.21 Many vessels may make contact and form anastomoses; however, few survive.15 In addition to recipient vessel activity, graft vessels may also actively proliferate and initiate connections to the recipient site.38 The formation of anastomoses between the graft and recipient site vessels and the resultant blood flow into the graft vessels have an inhibitory effect on capillary bud proliferation in the recipient bed. If separation from the graft bed occurs because of seroma or hematoma formation, this inhibiting effect is reduced, and granulation tissue proliferation resumes.38 Marked vascular remodeling takes place in the graft as the result of random anastomoses of graft arteries with recipient bed veins and vice versa.6 Initially perfusion is slow when blood begins to flow in the graft vasculature on the third or fourth postgrafting day, but it continues to improve until normal flow velocity is reached by the fifth or sixth day.15 Vascular Ingrowth Grafts are also revascularized by the ingrowth of new vessels from the bed into the graft. These vessels may grow into the dermis or into preexisting graft vessels, which serve as nonviable conduits for new ingrowing vessels (see Figure 80.1C). If ingrowing endothelial cells contact areas of surviving endothelium in old graft vessels, anastomosis occurs, resulting in more rapid revascularization. New capillary ingrowth occurs at approximately 0.5 mm/d. Graft vessels that are not involved in inosculation or ingrowth of new vessels degenerate and disappear.18,53 Newly formed vessels are tortuous and irregularly dilated. Maturation of vessels begins within 48 hours after the appearance of new, undifferentiated capillaries. The vessels that receive most of the blood supply undergo an increase in diameter and lose their tortuosity, forming arterioles. This maturation and differentiation process continues until a new system of arterioles, venules, and capillaries has developed. As with ordinary second intention healing of open wounds, vascularization of the graft is under cytokine control. For example, levels of vascular endothelial growth factor are elevated in the graft, particularly from postgrafting days 5 to 7,40 corresponding with the peak of vascular ingrowth activity. In addition to blood vessels, new lymph vessels form for lymphatic drainage of the graft by the fourth or fifth day.74 Graft Appearance The progression of vascularization can be followed by observing characteristic color changes in the graft. When initially placed, grafts are pale. During the next 48 hours as inosculation begins, the graft may appear red to dark purple from congestion because inflow tends to exceed outflow. This gives way to a lighter reddish hue by 72 to 96 hours. By postoperative day 7 or 8, the entire graft is red to pink if survival is complete. A more normal, pale pink color gradually returns by day 14.73 Areas of avascular necrosis are indicated by persistently pale coloration (whitish or light tan); these areas will undergo necrosis and then slough. Dry ischemic necrosis may appear as black discoloration. A partial-thickness take may be characterized by dark discoloration because of vascularization of the deep portion of the dermis and ischemic necrosis of the epidermis and superficial dermis. This superficial necrotic layer forms a dark eschar on the graft surface. After this sloughs or is debrided, the underlying viable dermis reepithelializes from dermal adnexa. The final appearance of the graft in a partial-thickness take is one of sparsely haired, epithelialized skin. Reinnervation Reinnervation of grafts depends on the type and thickness of the graft, the amount of scar tissue formation, and the innervation of surrounding tissue. Reinnervation is better in full-thickness grafts than in split- thickness grafts.23 In the authors' experience, animals show signs of paresthesia as grafts reinnervate. At approximately 3 weeks after full-thickness grafting, most grafts appear to be fully healed, with normal skin color indicating a well-established vascular supply and strong connective tissue attachment to the wound bed. However, when bandaging is discontinued, the animal may persist in licking or chewing the graft. An additional period of bandaging may help protect the graft during this time of reinnervation. Elizabethan collars have been advocated for approximately 1 month postoperatively, with close observation during temporary removal.73 Types of Grafts A variety of different skin grafts have been used successfully in small animals. Split-Thickness Grafts Definition and Indications A split-thickness skin graft is composed of epidermis and a variable quantity of dermis. These grafts are classified as thin, intermediate, or thick, depending on the amount of dermis in the graft.14,21 The main indication for this type of graft in dogs is for reconstruction of defects with extensive skin loss.28 Because the skin of a cat is so thin, split-thickness grafts are not indicated.23 Technique of Split-Thickness Grafting Graft Bed Preparation Before grafting, the defect must be prepared to accept the graft. Chronic granulation tissue should be completely excised if it is present, and grafting should be delayed until a healthy acute granulation bed forms, usually within 4 or 5 days. In the presence of healthy granulation tissue, the epithelium at the wound edge is removed.51,54 The top of healthy granulation tissue may be lightly scraped, or the superficial 0.5 to 2.0 mm of granulation tissue may be tangentially excised with a sharp blade.51,55 Alternatively, the surface of the granulation tissue may be wiped with a gauze sponge to prepare for grafting.11 The defect is covered with a surgical sponge soaked in antiseptic solution (i.e., 0.05% chlorhexidine diacetate in normal saline) while the graft is harvested. Rinsing the wound surface with a 0.25% solution of neomycin in saline is an alternative.55 It is advisable to let natural hemostasis occur before applying the graft. If bleeding persists, it may be controlled by pressure or careful pin-point electrocoagulation.23 A fresh wound should be thoroughly debrided and lavaged with an antiseptic solution before grafting. If a minimal amount of devitalized tissue remains on the wound after surgical debridement, wet-to-dry dressings may be applied for an additional 1 to 2 days to hasten the removal of residual debris; at this point, nonadherent dressings are indicated to minimize further removal of granulation tissue at bandage changes.53 By using this method, a healthy granulation tissue bed for grafting can usually be established within 5 to 7 days. An alternative is to perform staged surgical debridement and lavage with a 0.05% chlorhexidine solution. Between debridement procedures the wound can be bandaged with a water-soluble antibiotic (e.g., silver sulfadiazine) and some of the new bandage materials that interact with wound tissues to enhance healing.64 The night before grafting, a nonadherent bandage should be applied with a thin coating of 0.1% gentamicin sulfate ointment.73 Graft Harvest Split-thickness grafts can be cut freehand with a manually operated graft knife. There are a number of designs available; most use some sort of cutting guide to help control the depth of the cut. The Goulian- type graft knife (Weck knife) (Figure 80.2) uses a disposable blade and has a fixed guard that slides over the blade. The Humby and Watson graft knives use an adjustable guard in the form of a round rod positioned in front of the blade. A convenient way to set the depth for these knives is to use a scalpel blade as a “feeler” gauge. An ordinary (not rib-back) #10 or #15 blade is approximately 0.35 mm thick, which is an ideal thickness for partial-thickness grafts in dogs. To set the depth, the scalpel blade is slipped between the graft knife blade and the guard, and the guard is adjusted until the distance between the guard and knife blade is equal to the thickness of the scalpel blade with no appreciable play.42 Partial- thickness grafts can also be harvested with an ordinary razor blade or a scalpel blade.46,57  FIGURE 80.2 Weck graft knife harvesting a split-thickness graft. Note the surgeon's use of the nondominant hand to provide traction away from the blade; this flattens and tenses the skin. A partial-thickness incision is made in the donor skin by a scalpel blade held perpendicular to the skin surface. After this initial incision has been made, a scalpel or razor blade is held almost parallel to the skin surface, and cutting is begun. After 3 to 4 mm of partial-thickness skin has been cut, three or four traction sutures are placed in the split thickness of skin to apply traction on it as the blade cuts the remainder of the graft (Figure 80.3). It may be necessary to use several blades before completing the procedure because the blades rapidly become dull. Cutting grafts with scalpel blades can be tedious, and the curved blade may be difficult to control when cutting grafts larger than 1 cm.74 Holes may inadvertently be cut in the graft as it is being harvested; however, these will heal, and they allow drainage from beneath the graft.29 FIGURE 80.3 Split-thickness graft harvest with a scalpel blade. A, Initial partial-thickness incision and traction sutures placed along one border to begin harvesting the graft. B, Partial-thickness graft before it is cut free at the base, releasing it from the donor site. Several types of power-driven dermatomes are available for harvesting split-thickness grafts, and these can be used on dogs. Perhaps the most widely known is the Brown dermatome, which uses a rapidly oscillating blade similar to an electric hair clipper. It is available in both electric- and gas- (nitrogen-) powered versions (Figure 80.4) and has been described to work well in harvesting split-thickness grafts from dogs.45 After aseptic preparation of the donor site, it is common practice to inject sterile physiologic saline or lactated Ringer's solution subcutaneously under the donor site to elevate and tense the skin. The skin should also be lubricated with sterile mineral oil or a sterile water-soluble surgical gel. These measures help ensure smooth progression of the dermatome as it is advanced. Good donor sites for grafts include the lateral thorax, the thoracolumbar region just lateral to the dorsal midline, the proximolateral aspect of the forelimb, and the lateral thigh.45 After a new disposable blade is placed in the dermatome, the thickness of the graft is determined by an adjustment on the instrument. The thickness of the graft can be selected from 0 to 0.76 mm (0 to 0.03 inch). A graft thickness of 0.38 mm (0.015 inch) is usually selected for use on dogs. The width of the graft is determined by interchangeable base plates used on the dermatome, ranging from 1 to 4 inches in width. The dermatome blade is lubricated with sterile mineral oil or water-soluble gel. The instrument is turned on, and the rapidly oscillating blade is advanced along the donor site, which is held taut by the surgeon and assistant surgeon. The assistant surgeon applies traction with fingers, a sterile tongue depressor, towel forceps, or stay sutures, while the surgeon applies countertraction with the free hand not operating the dermatome. After cutting has started, the dermatome may be continuously advanced, or the graft may be severed. Especially in cutting long grafts, a second assistant should use skin hooks, forceps, stay sutures, or two 20 gauge needles bent to serve as skin hooks to grasp and tense the graft as it comes from the dermatome. The power-driven dermatome is relatively easy to use, but it is an expensive instrument and thus may not be practical for occasional users. FIGURE 80.4 Nitrogen-powered Brown dermatome in use. Note the application of graft traction with forceps held by the assistant; this tenses the skin and makes cutting easier. Graft Placement After harvest the graft is placed on the recipient bed and oriented so that the direction of hair growth will be the same as that of the surrounding hair. The graft may be cut to an exact fit of the defect; however, many surgeons prefer the graft to overlap the edge of the defect by up to 1 to 2 cm. The overlapped portion of the graft will undergo avascular necrosis and can be excised later (Figure 80.5). Whether overlapped or not, the edge should be adequately secured with sutures or staples placed through the graft and surrounding skin. Additional sutures should be placed as needed in the central field of the graft to ensure good contact with the recipient bed.14,28 FIGURE 80.5 A, Split-thickness unmeshed skin graft sutured in place with simple interrupted sutures along the edges. The graft margins overlap onto normal skin by 1–2 cm, making a pattern unnecessary. B, The portion of the graft overlying the recipient bed has engrafted; the overlapping part has undergone necrosis and will slough. Donor Site Closure The donor site can be excised completely and the edges sutured together for an improved cosmetic result.60 Alternatively, the donor site can be covered with a sterile nonadherent dressing and antibiotic ointment or a petrolatum-impregnated gauze and treated as an open wound.19 The contact layer is covered with secondary and tertiary layers. The donor site heals by reepithelialization from the cut ends of hair follicles, sebaceous glands, and sweat glands, as well as from the wound edges.55 Disadvantages of open wound management of the donor site include the requirement for multiple bandage changes, prolonged healing time, and sparse hair regrowth.51 Aftercare After placement of the graft, blood clots can be removed from under the graft by applying pressure to expel them or by swirling a cotton-tipped applicator under the graft. Alternatively, a thrombin or saline solution may be used to irrigate underneath the graft before application of the dressing.10,14,21,36 Bandaging Antibiotic ointment can be placed around the graft edges, and a nonadherent dressing pad or a gauze pad impregnated with petrolatum can be placed over the graft. An absorbent conforming mesh gauze is wrapped over the area, followed by application of an immobilizing splint and tape or a split cast and tape that can be removed periodically for dressing changes. If the graft has been placed over a joint, the area is immobilized with a Mason metasplint, Schroeder-Thomas or spica splint, transarticular external fixation splint, or molded splint of casting material incorporated into the bandage. Immobilization is necessary until fibrous tissue anchorage is strong enough to withstand shearing strain without capillary rupture.36 Immobilizing splints are usually necessary for 10 to 14 days postoperatively.65 The frequency of bandage changes depends on the temperament of the animal and the cleanliness of the bandage. The first bandage is usually changed 48 hours after surgery.55 If a hematoma or fluid is noted beneath a graft when the bandage is changed, it can be removed by making an incision in the graft and applying gentle pressure over the graft or by using a sterile eye dropper or a cotton-tipped applicator to remove serum or blood.14,21,36,74 Because of the risk for contamination or graft movement, the longer the intervals between bandage changes, the better. However, frequent changes (i.e., daily) may be necessary if bandages become soiled with feces or urine, if an animal disturbs the bandage, or if infection is present. Bandage changes are performed carefully to avoid damage to the graft from movement and contamination.9,46 Physical restraint of the animal is always indicated, and chemical restraint may also be necessary.45,74,75 A tie-over bandage may be used for local immobilization and conformity of the graft and bed; it immobilizes grafts in difficult areas, such as on inner thighs and upper limbs.45 Several 2-0 or 3-0 monofilament nylon sutures with long ends are placed in the skin around the graft approximately 1 cm from the graft edge. A nonadherent pad is placed over the graft followed by a bolus of sterile cotton or gauze. The long ends of the preplaced sutures are drawn together over the bolus and twisted together until they pull the bolus gently down against the graft. One or two metal clips can be used to fix the twisted sutures near the bolus. Gauze, tape, and a splint or cast are used in addition to the tie-over bandage for more protection and immobilization. Gentle elevation of the edge of the tie-over bandage between some of the tie-over sutures allows inspection of the graft. Tie-over bandages are generally removed on the third or fourth postoperative day, followed by continued protective bandaging and immobilization until at least 21 days postoperatively.74,75 Negative-Pressure Wound Therapy More recently, advances in wound care have been applied to postoperative care of split-thickness grafts. Although the use of negative-pressure wound therapy (NPWT) is becoming more widespread, there is still a paucity of objective data that definitively support its routine use in this application, and reported results and conclusions from different studies are often conflicting. For example, in randomized clinical trials of human patients, the use of postoperative NPWT on split-thickness grafts was shown to improve the percentage of graft survival and the cosmetic appearance compared with a tie-over bandage or similar standard dressing.31,35,39 In contrast, a randomized experimental study in Yorkshire pigs comparing NPWT with traditional bandaging after split-thickness grafting81 failed to show a statistically significant difference, either histologically or in graft survival, although the investigators did feel that subjectively the grafts in the NPWT group had better adhesion and a nonsignificant trend toward better survival. Further randomized controlled studies are needed before NPWT can be recommended as a significant improvement in the standard of care for postoperative management of split-thickness grafts. Advantages and Disadvantages of Split-Thickness Grafts The thinner dermis of split-thickness grafts results in several potential advantages over full-thickness grafts. Foremost among these is that split-thickness grafts have better viability than full-thickness grafts. McKeever and Braden37 noted an 89% survival for thin partial-thickness grafts on dog forelimbs versus 58% for full-thickness grafts. This difference has been attributed to greater capillary density in the exposed dermal plexus of partial-thickness grafts compared with the subdermal plexus of full-thickness grafts. As a result, more graft vessels are available for inosculation with vessels of the recipient bed. In addition, ingrowing vessels have less distance to traverse in split-thickness grafts, which hastens the establishment of perfusion. Finally, the thinner dermis of the partial-thickness graft also means a shorter distance for diffusion and therefore improved cellular survival during the period of plasmatic imbibition.  If wound contraction causes problems (i.e., contracture deformity), a split-thickness graft may be advantageous in dogs. These grafts result in expansion of the graft area after healing. This expansion is greater with split-thickness grafts than with full-thickness grafts in dogs. Split-thickness grafts also have several disadvantages compared with full-thickness grafts. The thinner dermis means that the grafts may be less durable and more subject to trauma, making them of questionable use on canine limbs. The hair growth may be absent or sparse on a split-thickness graft, depending on its thickness, and if the donor site is allowed to heal as an open wound, its haircoat may be the same (Figure 80.6). Grafts may have a scaly appearance and lack sebaceous glands.a Graft harvesting requires special and sometimes expensive equipment.29 Blades that are used to harvest split-thickness grafts usually become dull rather rapidly.74,75 FIGURE 80.6 Split-thickness graft outcome. Note the thin hair growth and relatively poor cosmetic result at the healed recipient site (A) and a donor site that was allowed to heal by second intention (B). Full-Thickness Mesh Grafts Definition and Indications A full-thickness mesh graft is a piece of full-thickness skin into which numerous slits have been cut in parallel, staggered rows to allow the graft to expand in two directions to increase its size. Meshing provides drainage, flexibility, conformity, and expansion.23 There are three indications for mesh grafts: (1) to allow drainage from a wound that has minor levels of exudation, bleeding, or serum oozing at the time of grafting; (2) to cover large skin defect(s) when there is insufficient donor skin, such as in extensively burned patients; and (3) to reconstruct irregular (i.e., concave or convex) surfaces that are difficult to immobilize. Of these three indications, the most common is to allow drainage from the wound as the graft heals. Technique of Full-Thickness Mesh Grafting Graft Bed Preparation The recipient bed is prepared in a manner that results in a healthy granulation tissue bed or a fresh wound bed that is vascular enough to produce granulation tissue. Presence of a rim of new epithelium around the granulation bed is often a sign that the wound is ready for grafting. Readers are referred to the earlier sections on graft beds and split-thickness grafts for information on preparation of the recipient bed. Graft Harvest When full-thickness mesh grafting is to be performed on a recipient bed of granulation tissue, a #15 scalpel blade is used to remove the thin border of epithelial tissue from the wound edge when it is present.73 After the graft bed has been prepared and epithelium removed, a pattern of the wound is made by pressing a piece of sterile cloth or sterile paper drape material onto the wound to obtain an imprint in blood. The pattern is cut out with scissors and then laid on the previously prepared and draped donor site in such a way that the “lay” of hair growth on the graft will be the same as the hair surrounding the wound.65,67 The pattern must be placed on the donor site in the correct orientation (i.e., “blood side” down); if it is placed upside down, the graft will end up as the mirror image instead of the shape of the defect.73 The pattern is traced on the skin with a skin marking pen or a sterile splintered applicator stick dipped in methylene blue.51,65,67 After the graft border is laid out, the traced line is cut with a scalpel blade, and the skin graft is sharply dissected from the donor site. Cutting the graft 1 cm larger than the pattern and trimming as necessary during application has also been suggested.45 Another technique is to measure the wound at its widest and longest points and then mark the dimensions on the donor site and draw a rectangular graft from them.46 The rectangle of skin is then removed from the donor site. If the graft is to be expanded, its length will grow shorter as its width is increased; this must be taken into account during measurements. Graft Preparation The graft must be stretched flat and secured to facilitate the removal of all subcutaneous tissue. One method is to place the graft, dermal (subcutaneous) side up, on a piece of sterile cardboard secured with long segments of suture material placed at intervals around the edge of the graft. The suture ends are pulled through slits cut in the edge of the cardboard to stretch the graft.7,72,76 Another method is to tack the graft around a sterile roll of coadhesive wrap with skin staples. Other alternatives include stretching and pinning the graft to a sterile piece of thick corrugated cardboard with sterile hypodermic needles;74 affixing the stretched graft to a moistened, tightly folded towel with towel forceps; or leaving one end attached to the animal and draping the remainder over the surgeon's index finger.45 All of the subcutaneous tissue must be completely removed. A scissors with sharp tips, such as an iris scissors or sharp-sharp operating scissors (some prefer curved over straight), and a delicate pair of thumb forceps are good instruments for this task (Figure 80.7). The graft should be kept moist with sterile saline during the “defatting” procedure. When the subcutaneous tissue has been properly and completely removed, the exposed dermis will have a cobblestone appearance because of the exposed bulbs of hair follicles.45 During removal of the subcutaneous tissue, the surgeon may accidentally cut a hole in the graft; this is no cause for concern.  FIGURE 80.7 A full-thickness graft has been placed dermal (subcutaneous) side up on a piece of sterile corrugated cardboard and stretched out and secured between hypodermic needles placed along the edges. Sharp-sharp scissors and thumb forceps are used to remove all subcutaneous tissue from the graft. An alternative method has been described for the defatting procedure, incorporating the use of a high- pressure hydrosurgical handpiece designed for use in wound debridement.79 The use of this alternative method was tested in preparation of skin grafts from canine cadaver skin and in a clinical case in a dog. When compared with conventional methods of graft preparation (either scissors or scalpel blade) on 4 × 4 cm pieces of canine cadaver skin, the hydrosurgical technique was able to remove subcutaneous fat in the shortest time (1.5 minutes for hydrosurgical technique, 3.5 minutes for scalpel, and 9.5 minutes for scissors). No difference in graft quality between methods was observed histologically, and 100% take with a good cosmetic outcome and no complications was obtained in the single clinical case reported. After defatting, a #11 scalpel blade is used to cut parallel rows of staggered incisions in the skin; the size and spacing vary, but the incisions are usually between 1 and 2 cm long and between 0.5 and 2 cm apart (Figure 80.8). Grafts can also be meshed with a mesh graft expansion unit. This instrument consists of an aluminum block in which thin, square-ended, notched stainless steel blades are mounted in staggered parallel rows (Figure 80.9). The graft is placed on the block with dermal side down (haired side up). A Teflon or nylon roller is then rolled over the graft, pressing down firmly. This presses the graft onto the blades and makes the mesh cuts. Several passes may be necessary to ensure that the mesh holes are cut completely through the skin. Mesh expansion units are available with different configurations of blade spacing—the closer the blades are spaced, the greater the number of mesh slits per unit area of skin, resulting in a greater expansion ratio (i.e., expanded size to original size). Expansion occurs primarily in one direction only (width or length, depending on the orientation of the graft on the meshing block); expansion ratios of 3 : 1 to 4 : 1 seem to work best with dogs and cats.52,67,72,76  FIGURE 80.8 Graft meshing. A #11 scalpel blade is being used to cut staggered parallel rows of slits throughout the graft. FIGURE 80.9 Mesh graft expansion unit consisting of numerous parallel rows of staggered, notched blades mounted edge up in an aluminum block. The skin graft is placed dermal side down on the blade block, and the Teflon roller is rolled with moderate pressure over the graft. This presses the skin down onto the blades, cutting slits in the graft. Graft Placement After meshing, the graft is removed from the cardboard and placed on the wound with the direction of hair growth properly aligned. Sutures (simple interrupted, cruciate, or simple continuous) or skin staples are used to fix one edge of the graft to the skin along one edge of the wound. In cases where the graft was originally cut to fit the wound bed, a 2 to 3 mm margin of skin is trimmed from the free graft edge before it is sutured or stapled to the remaining wound edge.52,72 This results in expansion of the mesh sites. If a rectangular piece of skin was taken from the donor site, one edge of the graft is sutured to one edge of the defect; the graft is then trimmed to fit the defect, and then the remainder of the edges are sutured in place.46,65,76 After the edges are sutured, the graft is further secured by placing simple interrupted sutures between the slits in the graft and around the graft tissue at strategic points where contact is not firm or motion is likely to occur, (e.g., places where the graft lies over a convex or concave part of the wound surface). Additional sutures are spaced throughout the graft field but not through all adjacent slits (Figure 80.10A).b FIGURE 80.10 A, A full-thickness mesh graft sutured with multiple simple interrupted sutures into a recipient site on a dog's distal forelimb. Note the sutures placed in between mesh openings to help secure the center of the graft, and the large expanded mesh openings. B, Three weeks after grafting. The mesh openings have healed by second intention and are contracting. C, Three months after grafting. The healed mesh openings are now virtually indistinguishable. Hair regrowth is beginning, and the cosmetic result should be good to excellent. Donor Site Closure The skin of the donor site is undermined and the defect closed by advancement of the skin edges. Tension- relieving techniques are indicated if excess tension is encountered. Aftercare Bandaging A very thin coating of antibiotic ointment (e.g., 0.1% gentamicin sulfate) is evenly spread over a sterile, nonadherent absorbent dressing pad before it is placed on the graft. Excessive ointment on the dressing may flow into the open mesh slits and then under the graft, where it could interfere with graft take; the authors have seen this happen. The contact layer is followed by a secondary layer of open meshed roll gauze followed by cast padding; these layers provide absorption, cushioning, and mild compression to ensure good contact with the recipient bed. The tertiary outer layer provides protection from the environment while remaining breathable and is composed of either porous adhesive tape (not the waterproof variety) or a coadhesive elastic bandage material.51,67,72,74 A Mason metasplint is included in limb bandages, especially if the graft is over a distal joint. Other means of immobilizing joints with grafts are a Schroeder-Thomas splint, a transarticular external fixator, or a molded splint of casting material incorporated in the bandage.65,76 Bulky bandages, slings, casts, or spica splints for upper leg wounds have also been described.45,46 In general, splints are needed only during the first 10 to 14 days after grafting; bandaging is usually continued for at least 21 days. Bandages are usually changed daily during the first week. As healing takes place and wound drainage decreases, the bandage is changed less frequently.65,67,73,76 Managing Superficial Infections A superficial infection may occasionally develop on the surface of the graft as a result of overgrowth of normal skin organisms on abnormal skin. The infection is limited to the graft surface and usually does not significantly affect the success of engraftment. Gentle cleaning of the graft surface with 0.05% chlorhexidine solution in saline along with a topical broad-spectrum antibiotic ointment controls infection.52 Adjunctive Postgraft Therapies—Hyperbaric Oxygen Therapy and Negative-Pressure Wound Therapy Advanced techniques in open wound care have been applied to the postoperative care of grafts in an effort to improve the percentage survival or to speed the process of engraftment. Hyperbaric oxygen therapy (HBOT) has been advocated as an adjunctive treatment for open wounds and for skin flaps, where it has shown some promise. In a randomized experimental trial of grafted distal limb wounds on horses, postoperative hyperbaric oxygen therapy was evaluated as an alternative to standard postgraft care. Hyperbaric oxygen therapy resulted in a trend toward less granulation tissue production and less edema but more inflammation and lower percentage viability.25 In a study of full-thickness mesh grafts in dogs, the authors reported only 13% viable graft at 10 days post grafting in dogs treated with hyperbaric oxygen therapy. Administration of deferoxamine concurrent with hyperbaric oxygen therapy improved survival to 65%; however, this is still significantly below expected graft survival. The authors concluded that hyperbaric oxygen therapy is detrimental to graft survival.26 In other experiments, hyperbaric oxygen therapy increased the level of postgrafting lipid peroxidation in skin grafts in rats33 and reduced vascular ingrowth in Yucatan minipigs.30 In summary, until more is known and the negative effects of hyperbaric oxygen therapy can be ameliorated, it appears to be contraindicated as an acute postoperative adjunctive therapy for grafts. Negative-pressure wound therapy (NPWT) has also been applied to skin grafts during the acute postgraft phase before graft take. Although most published reports of postgrafting NPWT are case reports and therefore lack a control group, early evidence indicates that the use of NPWT appears to be beneficial, or at least not harmful, to graft survival. In one experimental study that compared several measures of skin grafting success for NPWT against standard bandaging,61 the authors noted earlier appearance of granulation tissue, more rapid contraction of graft mesh holes, earlier adherence of grafts to recipient bed, and reduced early graft necrosis at day 7 (1% for NPWT vs. 10% for bandaged grafts). Histologic scores between the treatments did not differ, however, and final results as measured by percentage take were also equal by day 17 of the study. Nevertheless, early postgrafting results were encouraging, particularly the tendency for grafts to adhere earlier with NPWT. The authors concluded that NPWT is superior to standard bandaging and have adopted NPWT as the institutional standard of care for postgraft management.48 In a case series involving 10 full-thickness grafts applied to 6 feline patients,43 NPWT was applied before grafting as an aid to recipient bed preparation and after grafting in an effort to improve take. NPWT was applied to all grafts for 3 days after grafting, with excellent results—7 of 10 grafts achieved 100% take, 2 had 95% take, and 1 had 80% take, for an overall average of 97%. This is slightly higher take than in previously published reports. Two aspects were particularly encouraging. Graft adherence was uniformly rapid—9 of the 10 grafts were already firmly adhered to the recipient bed by day 3 after grafting when NPWT was discontinued; in the remaining graft, partial detachment was attributed to an unresolved Pseudomonas infection at the time of grafting. Also, 3 of the patients had grafts applied to locations on the abdominal wall—normally a challenging location because it is very difficult to achieve good compression of graft to recipient site via truncal bandaging in a cat. Two of the 3 abdominal grafts had 95% take, with the third only 80% owing to the aforementioned infection. Overall, NPWT as an alternative to traditional bandaging for management after placement of full-thickness mesh grafts appears promising and warrants further investigation. Advantages and Disadvantages of Full-Thickness Mesh Grafts Mesh grafts have several advantages over other, nonmeshed grafts. Viability is excellent, with 90% to 100% take for grafts that are applied on healthy granulation tissue and receive proper postoperative care.23 One major benefit is improved drainage through the mesh holes, thus preventing formation of hematomas or seromas that would disrupt graft-bed contact and impair revascularization. Meshing also improves conformability of grafts applied to convex, concave, or otherwise irregular surfaces. Part of the reason for this is that the graft is affixed to the wound surface by sutures through the slits. Additional stabilization is provided as granulation tissue grows upward into the mesh holes; additionally, this granulation tissue serves as a source of vascular supply for the graft, as vessels grow from these plugs of tissue laterally into the adjacent dermis.76 As the graft heals, the mesh holes contract and become inconspicuous (see Figure 80.10B–C). Meshed grafts also retain all the advantages associated with full- thickness unmeshed grafts. A potential disadvantage of meshed grafts is that excess granulation tissue may grow up through the slits and over the top of the graft.67 Grafts that are meshed with a scalpel blade are not as expansible as those meshed with a mesh graft expansion unit.45 It has been stated that a diamond-shaped pattern consisting of narrow tufts of hair between epithelial scars results when the graft is meshed with a mesh graft expansion unit.51 However, the authors have found that even large expanded mesh holes contract to small scars that are usually covered by hair from the adjacent skin of the graft (see Figure 80.10B–C). Split-Thickness Mesh Grafts Mesh grafts can also be prepared from split-thickness skin. In general the best results are obtained when the grafts are harvested with an electric- or air-driven dermatome, as described earlier for split-thickness nonmeshed grafts. The graft may be meshed with a scalpel blade as described earlier or by placing the graft dermal side down on a mesh graft expansion unit (see Figure 80.9). These grafts are used to cover large surface area defects when there are limited donor sites (Figure 80.11A).72 FIGURE 80.11 A, Expanded mesh graft covering a lumbosacral wound; note epithelialization covering the open mesh spaces as the site heals. B, Hair regrowth at 2 years after grafting. Because a pattern is not used with a split-thickness graft, the graft edges often overlap the skin surrounding the wound. Interrupted sutures or skin staples secure the graft to the surrounding skin, and tacking sutures are used between mesh holes of the graft to fix it to the recipient bed.45 The aftercare of these grafts is the same as for full-thickness mesh grafts. These grafts have the same advantages as a full-thickness mesh graft and the additional advantage of being thin skin that revascularizes rapidly. When expanded, the openings in the mesh heal by contraction and epithelialization, which is unattractive in the early stages of healing. With graft maturation, the cosmetic appearance improves as some hair regrows; however, hair coverage may be sparse because split- thickness grafts do not contain a full complement of hair follicles (see Figure 80.11B). Full-Thickness Unmeshed Grafts Definition and Indications A full-thickness unmeshed graft is prepared just like a full-thickness mesh graft, but no slits are cut in the graft. These grafts are indicated for prevention of postgraft contraction, which might result in contracture, particularly on the distal limbs and over joint surfaces. Their use should be limited to noninfected granulation beds with minimal to nil fluid production because, with an unmeshed graft, any wound fluid would accumulate beneath the graft and push it off the recipient bed, resulting in engraftment failure.23 It has been recommended to use unmeshed grafts to close small- to moderate-sized wounds on the distal extremities. Technique of Full-Thickness Unmeshed Grafting The graft is placed on the wound so that the lay of the hair growth is the same as on the surrounding skin. Several 3-0 or 4-0 nonabsorbable monofilament stay sutures are placed at key points around the graft to position it and provide mild tension for better conformity and contact, and the remaining edge sutures are placed. Either simple interrupted or continuous suture patterns may be used, with sutures 3 to 4 mm apart (Figure 80.12). Alternatively, surgical staples can be used for graft fixation. To avoid hemorrhage and consequent hematoma formation, grafts are not sutured in the central portion of the wound bed. If the graft is cut larger than the wound, it will overlap the wound edge; the overlapping portion undergoes necrosis and is trimmed away at 7 to 10 days.46 FIGURE 80.12 A full-thickness unmeshed graft sutured in place on a paw wound. Fluid Drainage For removal of wound fluid from beneath a small unmeshed graft, a small closed suction drain can be placed before placement of the graft on the bed. The wound is lavaged to remove tissue fragments and debris that could plug the drain. The Luer-Lok adaptor of a 19 gauge butterfly catheter is cut off of the tubing, and holes are cut in the sides of the tubing. A stab incision a little smaller than the diameter of the tubing is made in the skin approximately 1 cm below the distal aspect of the wound. The cut end of the fenestrated catheter tube is passed through this incision across the graft bed to the far side of the graft bed edge, allowing the tubing to extend straight across the wound. A subcutaneous tunnel is then made at this point extending 1 cm beyond the edge of the graft bed. The end of the tubing is inserted into the tunnel and secured to the overlying skin with a suture placed through the skin and tubing. Suture ends are left long so the suture can be cut before drain removal. The tubing is adjusted to lie flat against the graft bed and then similarly secured ventrally. The graft is placed on the bed over the tubing and secured at its edges. A small (2 to 5 mL) evacuated blood collection tube is immediately placed on the needle of the butterfly catheter to prevent clots from forming in the tube and to provide suction to remove drainage (Figure 80.13).50 For a large graft, it may be necessary to place a second drainage apparatus at another point under the graft for adequate drainage. As with any closed suction drain, success depends on the establishment of an airtight seal all the way around the wound edge. Another method to establish drainage is to cut one or two stab incisions in the graft.45 However, blood may clot in these incisions, resulting in poor drainage. FIGURE 80.13 Placement of a closed suction drain. A, The Luer-Lok adaptor from a 19 gauge butterfly catheter has been cut off, and the tubing has been fenestrated. The tubing is passed across the wound through a small stab incision and then fixed in place under the skin edge with percutaneous sutures on either side of the wound. B, The graft is sutured in place over the drain. C, The needle of the butterfly catheter is inserted into an evacuated blood collection tube. (From Swaim SF: Skin grafts. Vet Clin North Am Small Anim Pract 20(1):165, 1990.) Aftercare Bandaging of the graft is performed as described for split-thickness graft. The evacuated tube is incorporated into the bandage in a way that it can be replaced when full without changing the entire bandage. When no further fluid is drained from under the graft by the evacuated tubes, usually after 48 to 72 hours, the closed suction apparatus is removed.54 The need for tie-over bandages is not as critical for holding the graft against the bed if an effective closed suction apparatus is used. As with split-thickness grafts and mesh grafts, bandaging is continued for at least 21 days postoperatively. Advantages and Disadvantages of Full-Thickness Unmeshed Grafts Full-thickness unmeshed grafts become pliable and movable over subcutaneous tissues; they resist trauma and are more like normal skin in color, texture, elasticity, and hair growth than split-thickness grafts.c Some studies of dogs have shown full-thickness unmeshed grafts to take as well as or better than split- thickness grafts. Postoperative contraction is minimal, and the graft area increases after healing.3 Full- thickness unmeshed grafts also provide adequate protection, and no expensive equipment or technical help is required.56 Because of the added advantages of meshing, however, most surgeons prefer to mesh all full-thickness grafts.  Full-thickness unmeshed grafts have certain disadvantages. They do not survive as well as split- thickness grafts in the presence of infection.28,29 This is particularly true when there is no provision for drainage. They also may not survive as well as full-thickness meshed grafts unless drainage is provided. The hair growth may not be as thick as on skin flaps because of damage to the bases of hair follicles during subcutaneous tissue removal; however, it should be better than either meshed or partial-thickness grafts.74 Pinch and Punch Island Grafts Definition and Indications Pinch and punch grafts are small pieces of skin placed in a granulation tissue bed with regular spacing between the grafts. These grafts are harvested by elevating a piece of skin and cutting it free (pinch graft) or cutting it as a plug with a biopsy punch (punch graft). These grafts are indicated for grafting granulating wounds, small wounds on the limbs, contaminated wounds or wounds with low-grade infection, wounds over areas not requiring durability, and wounds with an irregular contour. These grafts are also indicated when placement of the graft below the wound surface will protect it from rubbing by the bandage or surrounding tissue (e.g., axillary wounds). They are generally used to promote epithelialization.45,46,70,74 Technique of Pinch and Punch Grafting Graft Bed Preparation Grafts are placed in a bed of healthy granulation tissue. Debris, necrotic tissue, and chronic or exuberant granulation tissue are removed, and the wound is treated until a healthy bed of granulation tissue is present.70 Graft Harvest Pinch grafts may be harvested from the cranial lower lateral thoracic area, where the skin is thin and well haired. A hypodermic needle, straight intestinal needle, curved suture needle, or Adson forceps may be used to elevate or tent the skin. The top of the tented skin is cut off with a scalpel blade at a right angle to the direction of traction, with care taken not to include subcutaneous tissue with the grafts. The graft may also be taken full thickness.45 The result is a piece of skin 2 to 4 mm in diameter for a pinch graft.7,24,74 A 5-mm-diameter skin biopsy punch may be used to cut punch grafts from a piece of full-thickness skin that has been removed from the animal or directly from the donor site on the animal (Figure 80.14). During insertion into the donor site, the punch is angled parallel to the direction of the hair follicles to increase the number of follicles per graft. All subcutaneous tissue is removed from each plug before it is placed in the graft bed.7,45,70  FIGURE 80.14 Harvesting punch grafts with a disposable Keyes dermal biopsy punch. Graft Placement To place pinch grafts in the granulation tissue, small slit-like pockets are made in the granulation tissue at a shallow angle—approximately 20 to 30 degrees to the surface of the wound. The pockets are made 2 to 4 mm deep and wide, and approximately 5 to 7 mm apart (Figure 80.15), using a #15 scalpel blade. After each pinch graft is harvested, a pocket is made for its placement, and the individual graft is tucked deep into the pocket. Pocket creation, graft harvesting, and graft placement should not be performed as batched tasks, because to do so can result in confusion as to which pockets have been grafted and which have not. If oozing hemorrhage tends to float the graft out of its pocket, the graft may be held in place by forceps or direct digital pressure may be applied for 1 or 2 minutes.1,70,73 Pinch grafting is usually reserved for thin granulation tissue beds.70 After the graft is placed in the pocket, it may be difficult to ascertain whether the direction of hair growth is correct.  FIGURE 80.15 Creating pockets in the recipient bed to receive punch or pinch grafts. A #15 scalpel blade is inserted at approximately 20 degrees to the surface to create the pockets. For placement of punch grafts, cylindrical holes 1 to 2 cm apart are cut in the granulation tissue bed. A 4-mm-diameter skin biopsy punch is used, and small scissors are used to remove the core of the granulation plug. The holes are made in staggered rows. To control hemorrhage from these holes, a cotton-tipped applicator is placed in each hole for approximately 5 minutes before the graft is placed.70 To prevent blood from obscuring the surgical field, the surgeon works from ventral to dorsal in placing grafts.62 As healing progresses, epithelium grows from each graft edge to cover the granulation tissue between grafts. Epithelialization also takes place from the wound edges (Figure 80.16).1,29 The length of time necessary for bandaging is a matter of clinical judgment depending on when the grafts are adequately healed and the wound is epithelialized.  FIGURE 80.16 A, Newly placed pinch grafts in a granulation tissue bed. B, The same recipient bed 3 weeks later. Note that the epithelialization is spreading from the periphery of each pinch graft and from the wound edge. Also note that some pinch grafts have no apparent zone of epithelium; these were additional pinch grafts placed approximately 2 weeks after the first ones. Donor Site Closure The donor sites may be bandaged and allowed to heal by second intention. Alternatively, the entire donor site area may be surgically excised and closed as a single large defect,74 or a simple interrupted suture may be placed in each donor site.34 Aftercare As with sheet grafts, island grafts of all types require protection after grafting. The grafts are covered with a nonadherent contact layer such as a commercial nonadherent dressing pad with a thin layer of antibiotic ointment applied or a petrolatum-impregnated gauze. The area is wrapped with an absorbent, conforming, open mesh gauze followed by cast padding, with application of a splint if the wound is on a limb. Porous adhesive tape or coadhesive wrap is applied as the outer bandage layer. The first bandage is usually changed 3 to 4 days postoperatively, with care taken not to disturb or pull off any grafts adherent to the dressing. If the dressing adheres to the grafted wound, sterile saline warmed to body temperature is applied to soften the bandage and exudates, thereby loosening the attachment. Alternatively, additional ointment may be applied over the dressing, which is then left in place until it spontaneously separates, usually within 10 days.70,73 Changing the bandage every day for 5 to 7 days and then every 2 to 3 days until healing is complete has been recommended.7,65 Advantages and Disadvantages of Pinch and Punch Grafts Island grafts, including pinch, punch, strip, and stamp grafts, are simple to perform and require no special equipment. The grafts take quickly and reliably because of their relatively large ratio of surface area to volume compared with sheet grafts. This is because the deep surface and also the dermal circumferential edge are in contact with the recipient bed granulation tissue surface. Pinch and punch grafts are easily harvested with the use of local analgesia, and the donor sites may be closed with a single suture, as opposed to more extensive donor site closures with other graft types. The granulation tissue overlying pinch grafts placed in pockets tends to hold the grafts in place while they revascularize. Because they are open grafts, they allow wound drainage and withstand infection well. Finally, these grafts can be used on irregular surfaces that are small and not located over areas requiring durability.1,7,45,73 Certain disadvantages have also been noted with island grafts. Particularly with pinch and punch grafts, excessive bleeding of the graft bed may float the graft out of its recipient pocket or delay graft revascularization. All island grafts generally have a poor cosmetic appearance with sparse hair growth and are often dry and scaly looking. This is because the only sources of hair follicles and oil glands are the relatively tiny implanted areas of dermis. The remainder of the recipient bed is covered with neoepithelium from keratinocyte proliferation and migration (see Figure 80.16). This thin epithelial covering is also relatively delicate and prone to injury compared with normal skin.46,65 Strip Grafts Definition and Indications Strip grafts are 5-mm-wide strips of skin that are placed in parallel grooves cut in a granulation tissue bed. The grooves in the granulation tissues are approximately 2 mm deep and 3 to 5 mm apart.66,71 These grafts are indicated for grafting granulation wounds. Wounds that are parallel to the long axis of the limb lend themselves to this type of grafting.73 Strip grafts are also indicated for irregular surfaces that are small and not located over areas requiring durability.45 Technique of Strip Grafting Graft Bed Preparation As with seed grafts, the graft bed must be composed of healthy granulation tissue. Debris, necrotic tissue, and chronic or exuberant granulation tissue are removed, and the wound is treated as an open wound until a healthy bed of granulation tissue is present.8,71,74 Graft Harvest The cranial lower lateral thoracic area is a good donor area for strip grafts. After the area is prepared for aseptic surgery, the strips are drawn on the donor area with a sterile marking pen or a splintered sterile applicator stick and methylene blue. The parallel longitudinal lines and one end of each graft are cut, and the remaining ends of the grafts are left attached to the body. Thumb forceps are used to grasp the cut end of each of the grafts. The graft is elevated by blunt dissection with scissors while traction is held with thumb forceps. With this traction on the graft, scissors are run down the back of each graft strip to remove subcutaneous tissue from the graft (Figure 80.17). The remaining end of the graft is cut free.66,71 Strips of skin 3 to 5 mm wide may also be cut from a rectangular segment of skin that is the same length as the wound. If this option is selected, the rectangle of skin is defatted before the strips are cut.45  FIGURE 80.17 Strip grafting. A, Removing the subcutaneous tissue from a strip graft by sliding scissors down the dermal side of the strip while it is still attached at one end. B, Cutting the troughs in the recipient granulation tissue bed. Graft Placement and Donor Site Closure Longitudinal incisions are cut in the granulation tissue approximately 3 to 5 mm apart. The edges of the incisions usually retract sufficiently to form grooves wide enough to accommodate the 5-mm-wide strip grafts (see Figure 80.17B). After hemostasis is attained on the graft bed by packing with gauze strips or umbilical tape, a strip graft is laid in each groove with hair growth going in the same direction as the hair around the defect. Simple interrupted sutures are used to anchor each end of each graft and to anchor grafts to the grooves at intervals along their length (Figure 80.18).65,66,71 The donor site is closed by undermining and advancing the skin edges together with deep and superficial sutures.66 Aftercare, advantages, and disadvantages were described earlier (see section on pinch and punch grafts).  FIGURE 80.18 Strip grafts sutured in place with sutures at the ends and along the length in several places. Stamp Grafts Definition and Indications Stamp grafts (chessboard grafts) are made from split-thickness or full-thickness skin that is cut into square patches. The patches are placed on a healthy bed of granulation tissue.23,45,46,74,75 These grafts are indicated for grafting granulating wounds. Aftercare was described earlier (see section on pinch and punch grafts). Technique of Stamp Grafting A piece of skin is harvested and prepared as either a split-thickness or a full-thickness graft (see earlier sections on split-thickness and full-thickness grafts). The skin is cut into roughly square patches that measure from 5 mm to 2 cm on a side. The grafts are placed on a healthy granulation tissue bed with 1 mm to 1 cm spacing between grafts. Depressions may be cut in the granulation tissue to accommodate each graft and to protect it from movement of the overlying bandage.46,74 The donor site for the graft is treated like any graft donor site (see earlier sections on split-thickness and full-thickness grafts). Advantages and Disadvantages of Stamp Grafts No expensive equipment is necessary for performing stamp grafting, and stamp grafts can be used on irregular wound surfaces. However, if grafts are placed on the surface of the granulation tissue, they are subject to movement and displacement if the bandage moves or when the bandage is changed. Cutting depressions to accept the grafts may be time consuming, and hemorrhage may necessitate packing the area to attain hemostasis before the graft is placed in the depression. As an open graft, this form of grafting allows drainage from the wound. As healing occurs, epithelial tissue grows from the edges of the stamp grafts to cover the granulation tissue between the grafts. These grafts do not have a good cosmetic appearance.45,74 Paw Pad Grafts Definition and Indications Pad grafts are small segments of full-thickness pad tissue taken from other paw pads on the same animal. The grafts are placed in recipient sites that have been prepared around the edge of a granulation tissue bed that has formed in the area of an absent metacarpal or metatarsal pad. After grafting, healing via contraction, epithelialization, and hyperplasia forms a durable weight-bearing tissue.63,68,69 Pad grafts are indicated when loss of some digits precludes use of a phalangeal fillet to replace a pad or in instances when a phalangeal fillet is not indicated or desired. The size and activity level of the patient should be considered before pad grafts are used for a pad salvage procedure. In large active dogs, pad grafts are less likely to be successful, especially when all of the digits and metacarpal or metatarsal pad have been lost and pad grafts are being used to produce a weight-bearing surface on the end of the metacarpal or metatarsal stump.65 A novel variation of the pad graft has recently been described,44 in which the third and fourth digital pads were harvested and transferred to the ipsilateral metatarsal stump to create a weight-bearing surface for a hind paw. In this dog, all the digits had become nonviable due to necrosis, but the pad skin from the nonviable digits was able to be saved for transfer. The novel aspect of the procedure was the ability to maintain a thin pedicle of viable granulation tissue that connected the primary wound bed to the paw pads being transferred. In this sense the grafts in question could not be considered strictly as free grafts because connection was maintained via the pedicle. However, because they were also not true pedicle flaps (because there was no pedicle of skin connected to the transferred pad skin), they must be considered as a new classification of skin graft. Negative-pressure wound therapy (NPWT) was used in this case, both before and after transference. The exact role that NPWT played in the successful graft take cannot be known with certainty because there was no control (without NPWT); however, it certainly seems logical that NPWT was beneficial in this regard, and owing to the difficulty commonly encountered with pad graft take, further investigation of this interesting variation appears to be warranted. Single-Stage Technique: Segmental Grafting Graft Bed Preparation The metacarpal or metatarsal pad wound is treated as an open wound until a healthy bed of granulation tissue is established. Rectangular tissue segments 6 × 8 mm are traced at intervals around the periphery of the recipient site by use of a template of x-ray film with a hole in its center. A skin marker or a splintered sterile applicator stick dipped in sterile methylene blue is used for tracing the border. The rectangles are incised with a #11 scalpel blade. Iris scissors and thumb forceps are used to remove the tissue, resulting in a series of rectangular depressions approximately 2 mm deep around the wound (Figure 80.19).8,9,44,63  FIGURE 80.19 Pad grafting technique. A, Rectangular patterns have been traced around the wound border, and the recipient sites are being excised. B, Rectangular patterns traced on donor sites and grafts being harvested. C, All subcutaneous fibroadipose tissue is removed from the dermal side of the grafts. D, Grafts sutured into the recipient sites with a single suture in each corner. Graft Harvest The template and skin marker are used to trace the same number and size of rectangles in the center of other digital pads on the same animal, possibly the same paw. The #11 scalpel blade is used to incise the grafts. Iris scissors and thumb forceps are then used to excise the grafts, and all subcutaneous tissue is removed from the grafts with iris scissors (see Figure 80.19B–C). A graft is placed into each rectangular depression and sutured. A simple interrupted suture of 4-0 to 5-0 monofilament nonabsorbable suture material is placed either in the center of the long sides or in each corner of the graft to secure it in place (see Figure 80.19D).8,9,44,63 Aftercare Grafts are covered with a nonadherent pad that has a thin layer of 0.1% gentamicin ointment applied. The secondary layer is composed of a moderate layer of open mesh cushioned gauze followed by a “doughnut” made from cast padding and covered with more cast padding. This layer provides absorbency, and the doughnut redistributes pressure away from the grafted area. Further offloading is accomplished by the incorporation of two metal Mason metasplints over the cast padding. One is placed on the palmar or plantar surface and the other on the dorsal surface in the configuration known as a “clamshell” splint. The splints are applied with the paw cups facing each other and extending approximately 1 inch beyond the end of the bandage.8 On the forelimb these splints may need to extend to near the elbow and on the hindlimb to the hock. The tertiary layer is composed of a thin layer of stretch-conforming gauze to secure the splints, followed by porous adhesive tape or coadhesive wrap. A similar bandage is used for the graft donor sites (which may be the other pads on the same foot); these are allowed to heal as open wounds. Sometimes if the remaining digital pad tissue is pliable enough, the donor sites may be sutured with far-near-near-far sutures of 3-0 monofilament nonabsorbable sutures; bandaging as described earlier is still necessary because without it, the pressure of weight bearing will cause the sutures to pull through the tissue. The initial bandage over the grafts is changed 3 days postoperatively and then every second or third day until at least 21 days after surgery. If it is believed to be necessary, a boot may be used in the transitional period between bandage and no bandage.9,44,59,63,68 Sutures are removed from grafts between 10 and 14 days postoperatively. At this time a hard, darkened stratum corneum lifts off each graft (Figure 80.20).8,9 FIGURE 80.20 Pad graft healing. A, Approximately 3 weeks after grafting. Note the coalescence of individual grafts into a single pad and loss of stratum corneum, causing a depigmented appearance. B, Six months after grafting. A normal thick covering of pad skin is restored with normal pigmentation. Two-Stage Technique A two-stage technique involving pad grafts and a bipedicle pouch flap has been described for autografting the pads to a paw stump. This technique is an option when the paw has sustained severe damage that requires amputation of all the digits, usually at the level of the metacarpophalangeal or metatarsophalangeal joints. In some instances the pads remain in viable condition and are available for reimplantation. Graft Harvest The fibroelastic pad tissue is completely removed from the pads to expose the dermis; this is analogous to removing the subcutis from a haired skin graft. The pad skin over each digit has a natural convex or “cupped” shape; thus each one must be split so that it will lie flat. Graft Placement An implantation site is prepared by removing the skin on the appropriate location on the trunk. Each pad graft is sutured to the cutaneous trunci muscle, and a tie-over or trunk bandage is applied over the grafts to hold them in place for 7 days.45 After 7 days a bipedicle pouch flap incorporating the pad grafts is elevated. The injured paw is placed beneath the flap (which contains the pads), and the flap is sutured at its edges to the wound bed. The limb is bandaged along the animal's side for 14 days, followed by staged division of both pedicles. The staged division begins with half the width of the ventral pedicle; the other half is divided in 2 days. The divided segments are sutured to the wound borders.45 The donor wound bed is closed primarily or allowed to heal by second intention. Aftercare When the two-stage pad graft and bipedicle pouch flap technique is used and a flap has been transferred to the paw, a heavily padded bandage supported by a Mason metasplint is used on the paw until the grafts form a thick stratum corneum. As with the segmental pad grafts, a boot may be used after bandaging.45 Advantages and Disadvantages of Paw Pad Grafts Segmental pad grafts provide an alternative to phalangeal fillet for replacing weight-bearing pads. In the early healing process, tough keratinized epithelium grows from the edges of the grafts to cover the remaining wound. Later wound contraction coalesces the grafts to provide a durable weight-bearing tissue. In addition, pad spreading is an advantage of the technique. The grafted area may initially be small; however, it enlarges with weight bearing to compensate (see Figure 80.20).63,65 The two-stage pad graft and bipedicle pouch flap technique has the advantage of providing a thick subcutaneous layer that replaces the pad fibroelastic tissue.45 Segmental pad grafting requires making a wound to harvest grafts to correct another wound. However, they usually heal quickly and completely as open wounds. If severe paw trauma results in bone directly under the healed pad grafts, the bone pressure with weight bearing may cause pad graft trauma and failure, especially in an active dog.8,68 The two-stage pad graft and bipedicle pouch flap technique is technically demanding,45 and the pouch flap is often not well tolerated by very large or active patients or those with a nervous disposition. The technique also requires that the original pad be available for use in the procedure. Mucosal Grafts Definition and Indications Mucosal grafts are free segments of mucosa removed from a donor site and placed in a recipient area where mucosal coverage is needed. In small-animal surgery, mucosal grafts have been described for replacing a nictitans membrane,32 constructing a mucosal lining for an extension of a hypoplastic prepuce,49 creating a conjunctival replacement on skin used to repair eyelid defects,20,45 lining a reconstructed nasal passage,82 and for urethroplasty.84 Technique Although references describe specific techniques for different mucosal graft applications, it is possible that there could be a combination of the various preparation or harvesting techniques to suit a recipient site. For example, a mucosal graft to line a nasal passage could be obtained by the buccal or sublingual harvest technique. Clinical judgment of the surgeon is indicated for individual cases. Graft Bed Preparation A mucosal graft must be placed on a recipient bed that is either healthy granulation tissue or tissue that is vascular enough to produce granulation tissue. For the techniques presented here, this would be a fresh wound bed,49 the dermal side of a freshly raised transposition skin flap,45 or the granulation tissue tube formed in a nasal passage.82 In the situation in which mucosal grafts are to be used to resurface reconstructed nasal passages, a bed or recipient area must be prepared for the grafts. Appropriately sized silicone rubber (Silastic) tubes are inserted into the nasal passages where reconstructive surgery has been performed to reform the nasal area. The rostral ends of these tubes are sutured to the skin with interrupted sutures of 2-0 monofilament nylon to hold them in place82 (Figure 80.21). The purpose of these tubes is to provide forms around which granulation tissue will develop from traumatized or surgically disrupted tissue in the area. The tubular granulation tissue structures will furnish vascular beds for placement of mucosal graft linings.82 FIGURE 80.21 Silicone rubber tubes inserted and sutured into the nasal passages where reconstructive surgery has been performed. (From Welch JA, Swaim SF: Nasal and facial reconstruction in a dog following a severe trauma. J Am Anim Hosp Assoc 39:407, 2003.) Mucosal Graft Harvest Mucosal grafts are obtained from buccal or sublingual mucosa. These grafts are generally very thin, and some care must be exercised in harvesting the grafts. To obtain a buccal mucosal graft, the upper lip is elevated with stay sutures, skin hooks, or towel forceps. To control hemorrhage and elevate the graft from underlying tissue, 0.01% epinephrine solution can be injected under the mucosa. The graft is outlined with a skin-marking pen, marking it slightly larger than the defect it will cover because of shrinkage when it is harvested. A #15 scalpel blade is used to incise the graft.45 Skin hooks45 or stay sutures82 can be placed in the corners of the graft. These are used to elevate the graft as it is harvested and to expand or flatten the graft from the shrunken configuration it takes after it is harvested. Cutting the graft free from submucosal tissue can be done with a #15 scalpel blade45 or with Metzenbaum scissors.49,82 If any submucosal or muscle tissue is present on the graft, it can be removed with Metzenbaum scissors.45,84 If there will be concern about drainage from under the graft, it can be meshed with a #15 scalpel blade.45 For a sublingual mucosal graft, the animal is placed in lateral recumbency with the mandible retracted ventrally and the tongue retracted dorsally to expose the sublingual area. Most grafts are rectangular in shape, with the long axis of the rectangle being parallel to the long axis of the tongue (Figure 80.22). Care should be taken not to design the graft over the sublingual salivary duct or sublingual vessels.82 Demarcation, incision, and elevation of the graft would be the same as for a buccal mucosal graft. As with the buccal mucosal graft, submucosal injection of 0.01% epinephrine may also be used to control bleeding and elevate the mucosa. The donor sites for buccal or sublingual mucosal grafts are closed with 3-0 or 4-0 absorbable suture. FIGURE 80.22 Harvesting a sublingual mucosal graft. (From Welch JA, Swaim SF: Nasal and facial reconstruction in a dog following severe trauma. J Am Anim Hosp Assoc 39:407, 2003.) Application of Mucosal Grafts The technique for applying a mucosal graft depends on the location of the recipient site. When more than one graft is needed to cover an area, the grafts can be sutured in place and to each other with 4-0 or 5-0 absorbable multifilament suture (e.g., polyglactin 910).49,84 If the graft has been meshed, tacking sutures of similar absorbable suture material between some of the mesh holes will help immobilize the graft while it heals to the recipient bed.49 Conjunctival Replacement If a graft is to be used to replace conjunctiva on a transposition skin flap that will be used to reconstruct an eyelid defect (Figure 80.23), the graft is sutured to the dermal side of the end of the skin flap using simple interrupted 4-0 or 5-0 absorbable multifilament sutures (e.g., polyglactin 910). The flap is then replaced in its original position and sutured in place for 4 to 7 days. At the end of this time, the graft should have healed to the end of the flap. The flap with the mucosal graft is elevated, transposed, and sutured into the eyelid defect.45 FIGURE 80.23 A, Tumor of lower eyelid. Designed transposition flap (solid lines) to correct the defect after tumor removal. B, Harvesting of a buccal mucosal graft. Note upper lip elevated with suture. C, Meshed mucosal graft sutured on the dermal side of the flap. D, Mucosal-lined flap returned to its original position. E, Mucosal-lined flap filling eyelid defect after tumor removal. (From Pavletic MM: Atlas of small animal reconstructive surgery, ed 2, Philadelphia, 1999, Saunders/Elsevier.) Nasal Mucosa Replacement If a mucosal graft is going to be used to resurface a nasal passage, approximately 10 days after placing the silicone tubes for formation of granulation tubes, the sutures holding the tubes in place are removed. The tubes are easily pulled from the nasal passages. The result should be healthy granulation tissue tubes that have formed around the silicone tubes.82 For each nasal passage, a mucosal graft is prepared and placed. After harvesting each mucosal graft, it is sutured with the submucosal side facing outward around a silicone tube that was removed from the nasal passage (Figure 80.24A). Simple interrupted sutures of 4-0 polyglactin 910 are used. Four removable traction sutures of 3-0 monofilament nylon are placed in the ends of the mucosal graft. Two doubled sutures are on either end of the graft, with the sutures on each end being 180 degrees apart (see Figure 80.24B). These are placed to hold the graft under tension to keep it smoothly stretched on the silicone rubber tube while it is reinserted into the granulation tissue tube that had formed around it during the previous 10 days.82  FIGURE 80.24 A, Suturing mucosal graft around silicone rubber tube with the submucosal side out. B, Placing traction sutures in the rostral end and nasal cavity end of the graft. C, Threading the traction sutures from the nasal cavity end of the graft back through the tube lumen. D, Inserting the tube and graft into the right nasal passage while exerting traction on the sutures. The traction sutures keep the graft smooth on the tube. E (inset), Three interrupted sutures hold the tube, graft, and skin edge, and three interrupted sutures hold the graft and skin edge. (From Welch JA, Swaim SF: Nasal and facial reconstruction in a dog following severe trauma. J Am Anim Hosp Assoc 39:407, 2003.) The traction sutures on one end of the graft are threaded back through the end of the silicone tubes to which they are closest. They come out the other end of the tube. Traction sutures at the other end of the tube are not threaded through the tube (see Figure 80.24C). The tube with the graft around it is inserted into the nasal passage. The end of each tube that has the two traction sutures threaded into it is inserted. Using gentle pressure, the silicone tube and graft are pushed in while traction is placed on all four traction sutures to keep the graft smoothly stretched during insertion (see Figure 80.24D). When the end of the tube and graft are flush with the rostral end of the granulation tissue tube, three equidistantly placed simple interrupted 3-0 monofilament nylon sutures are placed to suture the edge of the graft to the skin edge at the rostral end of the granulation tissue tube. Three additional sutures are placed through the silicone tube, the graft, and the adjacent skin, thereby creating a new mucocutaneous junction while anchoring the rostral end of the silicone tubing (see Figure 80.24E). After suturing, the two rostral-most traction sutures are removed by traction on one of their ends. The two caudal-most traction sutures emerging from the lumen of the silicone tube are then removed in a similar manner. The end result is a mucosal graft lining the previously formed granulation tissue tube, with the silicone rubber tube acting as a stent to hold it against the granulation tissue while it revascularizes and heals in place.82 Aftercare Aftercare of a mucosal graft depends on how the graft is applied. Preputial Reconstruction If the graft has been placed on a wound bed at the cranial end of a prepuce in preparation for forming a mucosal-lined tube for preputial extension (Figure 80.25), its aftercare will be similar to that of a mesh skin graft. A nonadherent semiocclusive pad with a thin coating of 0.1% gentamicin sulfate ointment should be placed over the graft followed by a secondary and tertiary bandage layer. The bandage is changed daily.49 FIGURE 80.25 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.  Because of their thinness, mucosal grafts revascularize and heal quickly. Similar to split-thickness skin grafts, they will have more secondary contraction than a full-thickness graft as they