Single pedicle advancement flaps (Fig. 19-2) are probably the most commonly used local flap employed in veterinary medicine because of their simplicity and the lack of a significant secondary defect requiring closure. Advancement (or sliding) flaps are rectangular in shape and are created parallel to lines of tension with an attachment at the base opposite the edge covering the wound. Paired advancement flaps resulting in an H-pattern of closure can also be employed although they are more complex. They may have better viability than one large flap, otherwise there is little significant advantage (Fig. 19-3). The single relaxing or release incision is a bipedicle advancement flap by design (Fig. 19-4).

Figure 19-2 Single pedicle advancement flap. Elevation of a single pedicle flap to reconstruct the cutaneous surface of the upper lip after resection of a large skin tumor.

Figure 19-3 Paired single advancement flaps resulting in an H-pattern to close a large rectangular defect on the thorax of a cat.

Figure 19-4 Bipedicle advancement flap. The releasing incision creates a flap with vascular supply on both ends of the flap. The resulting defect is left to heal by second intention.

Advancement flaps provide wound coverage by stretching the flap skin along its long axis over the defect, and as a result there is an opposing elastic retraction in the surrounding skin.

Rotating/transposition flaps

Rotation flaps are created by releasing the skin along an arc-shaped incision before moving it along the same axis. They are of limited use in feline reconstruction since relatively large areas of skin need to be raised to achieve wound coverage. The transposition flap is a rectangular pedicle graft, which instead of being moved along its long axis is rotated up to 90 degrees of the wound axis (Fig. 19-5). This is the most common type of rotating flap and is by far the most useful technique to close a variety of small sized problematic wounds. A modification of this flap is the front or hind limb fold flap.

Figure 19-5 (A) 90 degrees rotating flap. Two parallel skin incisions are made at an equal distance from the nipples. The length of the flap depends on the length of the defect that needs to be covered. (B) A 90 degree transposition flap. These flaps are used to reconstruct large rectangular defects involving adjacent sites.

Distant flaps

Direct distant flaps are raised at a location remote from the skin defect and ultimately transferred to the recipient bed by approximating the wound with the donor site. This technique is used almost exclusively for reconstruction of wounds involving the middle or lower extremities and provides durable full thickness skin coverage without the need for skin grafts.³ Flaps are normally raised on the flank and the affected limb brought alongside to allow the flap to be sutured to the recipient bed. Flaps may be single pedicle (hinge; Fig. 19-6) or bipedicle (pouch; Fig. 19-7) grafts. The limb must then be secured against the flank over a ten to 14 day period while the flap attaches to the wound. The pedicle(s) are divided, often in two stages, to complete the transfer.⁴ Cats are generally well suited to this technique and tolerate the period of limb immobilization better than dogs because of their size, flexible limbs, and the availability of ample loose elastic skin. Distant flaps are multi-staged procedures and consequently are time consuming and expensive. The transplanted skin assumes the same hair growth as its donor site despite its new location. Some patients will not tolerate their limb being immobilized against their flank and this is particularly evident if the limb is positioned in an elevated position. Occasionally, moist dermatitis caused by skin-to-skin contact and moisture accumulation is encountered; transient muscle atrophy of the limb may be noticed in some cases.

Figure 19-6 Single pedicle direct distant flap (hinge). These flaps are used to cover defects on the lower forelimb and hindlimb. The flap can be dorsally or ventrally employed depending on the location of the skin defect.

Figure 19-7 Bipedicle direct distant flap (pouch). Two incisions equal to the width of the skin deficit are made. The flap is undermined below the panniculus muscle. The limb is then secured beneath the flap and sutured.

Axial pattern flaps (Fig. 19-8)

An axial pattern flap is a pedicle graft based primarily or solely on the vascular supply of a direct cutaneous artery and vein.⁵ The vessels, of which terminal branches supply blood to the subdermal plexus, extend the length of the flap. Therefore axial pattern flaps have better perfusion compared to subdermal plexus flaps. Large axial pattern flaps can be safely elevated and transferred in a single-stage procedure for closure of major cutaneous defects. These flaps have excellent survival rates and they can be used to reconstruct wounds associated with less optimal conditions such as contamination, uneven surfaces, exposed bone, tendon, and cartilage. Axial or island pattern flaps are classified according to the vascular territory supplied by the direct cutaneous artery (angiosome). These vessels and territories including the thoracodorsal artery, lateral thoracic artery, omocervical artery, caudal superficial epigastric artery have been researched and mapped for clinical use as axial pattern flaps in the cat. Although the location and relative size of each angiosome are similar for both dogs and cats, the extreme elasticity of feline skin and the relative increase in body size to limb length often facilitates more distal coverage of limb wounds in cats.⁶ Axial pattern flaps sometimes require extensive dissection of the donor site for flap elevation; because of their relatively large size, axial pattern donor sites may require undermining and walking sutures to appose the defect created by the raised flap. The cosmetic appearance of the recipient bed differs from the donor site with regard to hair direction, color, length, glandular tissues, and amount of subcutaneous tissues.