Chapter 57 Selected Skin Graft and Reconstructive Techniques

Large skin wounds can occur (1) from trauma directly to the skin or to its blood supply; (2) secondary to necrotizing skin diseases (see Chapter 49); and (3) after removal of large skin, subcutaneous, or body wall neoplasms. Most open wounds eventually heal by the formation of granulation tissue, wound contraction, and epithelialization. Skin flaps or grafts are indicated when wound healing is either not progressing or will take a very long time for completion. Full-thickness skin is necessary to prevent mechanical problems caused by repeated trauma (e.g., in the dorsum of the leg or paw). Skin reconstruction is also necessary if the open wound is so large it will cause significant patient morbidity or wound contracture is likely to cause a significant problem (e.g., the wound is over a joint and the scar limits full extension and weight-bearing). Skin flaps are usually preferred over skin grafts because they are simpler to perform and have a higher success rate. However, if a skin flap is not feasible due to lack of adjacent skin (such as the distal limb), consider a skin graft.

Consider several factors before performing skin flaps or skin grafts, such as viability of adjacent tissue, systemic illness that may affect wound healing, function of the affected area of the body, tolerance of the wound by the animal, feasibility of long-term bandaging of the affected area, desired cosmetic result, and cost to the owner. Thoroughly discuss these factors with the owner prior to performing any of these procedures.

This chapter describes practical methods of reconstructing skin using skin flaps and grafts. More complicated methods of skin grafting that require specialized skill or equipment, such as using a dermatome for split-thickness skin grafts, microvascular flap transfer, or tube grafts, are not discussed in this chapter. Primary closure of skin wounds is reviewed in Chapter 55, and open wound management in Chapter 56.

SKIN FLAPS

Skin flaps are a means of reconstructing open wounds by rotating, transposing, or advancing adjacent or regional skin to allow wound closure. Blood vessels supplying these flaps are maintained. Therefore, skin flaps do not rely on a bed of granulation tissue in the defect for their early blood supply and nutrition. Skin flaps can be classified according to their blood supply, such as random subdermal flaps versus axial pattern flaps, or according to their location with respect to the recipient bed, such as local flaps versus distant flaps.

Random Subdermal Flaps

Random subdermal skin flaps are those constructed without regard to the presence of a direct cutaneous artery. Viability of these skin flaps is dependent on the availability of local subdermal blood vessels supplied in the flap base, so they rely on a wide skin attachment to insure adequate blood supply. Random subdermal skin flaps can be further classified as advancement flaps, rotation flaps, and transposition flaps, depending on how the flap is moved to the defect; single pedicle and bipedicle flaps, depending on how the flap is attached to the body; and direct distant flaps, moving an extremity wound to a distant region of redundant host skin for flap coverage.

• Advancement refers to how the flap is moved to the wound. These are usually rectangular flaps. Simple advancement flaps are undermined and pulled (horizontally or vertically) directly to the wound (Fig. 57-1).

• A transposition flap is a tongue-shaped flap, usually constructed immediately adjacent to the wound. It is rotated (clockwise or counterclockwise) to cover the wound (Fig. 57-2).

• A rotation flap is a semicircular flap that pivots into an adjacent recipient bed. Single or paired flaps can be employed to close triangular defects (Fig. 57-3); no secondary defect is created with this flap.

• Direct distant flaps include thoracic or abdominal single pedicle or bipedicle flaps that can be used as a method for transferring skin to the distal extremities.

• Single pedicle: Attached to the body only at one end (Fig. 57-4A, C). The pedicle provides the vascular attachment to the flap.

• Bipedicle: Attached to the body at both ends (Fig. 57-4B).

• These flaps are transferred from a distance to the recipient defect. The lesion is advanced to the flap rather than the flap being transferred to the lesion as in construction of advancement flaps.

• Forelimb defects are more often reconstructed using this technique than are rear limb defects.

Figure 57-1 Simple advancement flap. Make the initial incisions (A), then deeply undermine the flap and advance to the defect (B).

Figure 57-2 Transposition flap. After measuring the length of flap needed (A), make the incisions and rotate the flap to the defect (B). Suture the flap first and then close the remaining defect (C).

Figure 57-3 Create a curved incision in a stepwise fashion to close a triangular wound.

Figure 57-4 Direct distant flap. Make the skin flap using the lateral thoracic or abdominal skin. Suture the flap to the limb defect. This flap can have a single (A) or double (B) pedicle. Secure the limb to the lateral body wall with skin sutures placed between the leg and the body wall (C). Place a padded bandage around the body to help stabilize the elevated limb.

Indications

Advancement, Rotation, and Transposition Flaps

• For large skin wounds that are located in areas with adjacent loose, redundant skin (e.g., neck, flank, dorsal trunk) that allows formation and closure of defects remaining after flap transfer without tension.

• As a general rule, do not consider these flaps for wounds distal to the stifle, elbow, or tail head, since there is often not enough skin to close the donor site without excessive tension.

Direct Distant Pedicle Flaps

• For large wounds of the distal extremities in which local skin is not available or would be closed under excessive tension.

• These flaps are usually made from skin over the lateral thoracic or abdominal wall. The leg is attached to the side of the animal’s body for a period of time while healing of the pedicle to the extremity wound progresses. The pedicle is then removed from the thorax or abdomen and the leg returned to its normal position.

• These flaps are very successful, but patient tolerance is variable.

Preoperative Considerations

• Carefully plan the surgical procedure. Review vascular anatomy of the region. The size, location, shape, and condition of the wound dictate the type of flap.

• Check the health, looseness, and pliability of the skin adjacent to the lesion or wound to determine feasibility of the intended skin flap.

• Consider administration of prophylactic antibiotics, given intravenously at induction of anesthesia, if significant contamination of the surgical site is possible.

• Prepare the recipient bed preoperatively to ensure that the area is free of infection, foreign material, and necrotic tissue.

• Direct distant flap technique requires two surgical procedures to complete. The owner is made fully aware of the costs involved, the postoperative management, and the problems related to the prolonged immobilization of the leg. Hair direction and cosmetic problems are more common with distant techniques than with local flap techniques.

Key Point

Consider the mobility of the extremity that contains the defect when determining the location and type of direct distant flap. Make sure the leg opposite the host limb is able to accept the extra weight-bearing load. Evaluate the size and temperament of the patient. Smaller animals with calm dispositions seem to tolerate this technique best.

Surgical Procedure

Objectives

• To provide full-thickness reconstruction of a large skin wound.

• To avoid tension along the suture line.

• To create flaps that maintain viability and provide satisfactory cosmesis.

Equipment

• Standard surgical pack and suture.

• Measuring device to plan length and width of flaps.

• Sterile marking pen to draw incisions (optional). Sterile methylene blue and a cotton-tipped applicator can be as effective as a marker.

• A piece of sterile double-knit cloth or section of paper drape can be used as a pattern for designing flaps intraoperatively.

• Penrose (¼-½ inch) or closed suction drains (e.g., Jackson-Pratt drain).

Technique

Advancement or Transposition Flaps

1. Carefully position the patient to free up any available skin in the region and to reduce tension while the flap is being sutured.

2. Aseptically prepare a liberal amount of skin in the region of the proposed flap and donor sites.

3. Remove epithelialized portions of the granulation bed by sharp dissection (usually present at the edges of the granulation bed). Undermine attachments of skin at the margin of the granulation bed to free up the bordering skin.

4. Gently manipulate the skin margins surrounding the defect to ascertain the availability of adjacent local skin.

5. Optimally, the donor area has enough skin available to elevate a flap without leaving a secondary defect that cannot be closed primarily.

6. If possible, avoid choosing a donor area that may be subject to excessive motion or tension.

7. Choose the type of flap depending on the availability of skin, shape, and location of the defect and size of the area to be covered.

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