Definition

A skin flap (or cutaneous pedicle graft) is a portion of skin moved from one area of the body to another with an intact vascular attachment to its donor site. Flaps are indicated for large cutaneous defects where local tissues cannot be mobilised. They are capable of enhancing blood supply to a defect and covering body wall defects and areas difficult to immobilise, providing immediate protection with hirsute skin.

Classification

Blood Supply

Subdermal plexus flaps (random flaps) are elevated without intentional inclusion of direct cutaneous vessels and rely on perfusion via the subdermal plexi. Axial pattern flaps, however, incorporate a specific direct cutaneous artery and vein, using established guidelines for flap development. These flaps have an excellent blood supply and allow much larger flap development compared with subdermal plexus flaps. These flaps are not dependent on a cutaneous pedicle, and island arterial flaps are often created, thus enhancing mobility.

Distance/Direction from Donor Site

Local flaps are elevated adjacent to the defect and are advanced or rotated into place. Distant flaps are almost always employed for closure of defects involving the limbs. Distant direct flaps (pouch flaps and hinge flaps) are transferred by elevating the affected limb to the donor site prepared on the lateral thorax or lower abdomen.

Attachment to Donor Site

A single pedicle flap has one cutaneous pedicle. A bipedicle flap has two cutaneous pedicles and allows a longer flap to be created, although it is limited in mobility. Bipedicle advancement flaps can be used as a tension-relieving technique, and in pouch flaps. An island flap has no cutaneous attachment to the donor site, just a vascular pedicle for perfusion (e.g., island axial pattern flap).

Composition

Composite or compound flaps incorporate skin and other tissues such as muscle, fat, bone or cartilage. Composite flaps are used clinically in the dog, e.g., gracilis musculocutaneous flaps, labial advancement.

Useful Flaps for the Small Animal Practitioner

The following are descriptions and examples of flaps that show consistent survival and are feasible to do with good instrumentation and surgical facilities in practice. These flaps provide a solid reconstructive repertoire for the competent surgeon.

Rotation Flap

This is a semicircular flap of skin that rotates about a pivot point across a defect. It is ideal for triangular skin defects. The incision should be long enough to create a flap that has no tension on it when sutured into place, i.e., at least four times the space through which the flap is to be moved. The flap can be created progressively, undermining until adequate skin is available to cover the defect. Avoid backcuts into the base of the flap. One can also use bilateral rotation flaps for square defects.

Transposition Flap

This is a rectangular flap of skin that turns on a pivot point (less than 90 degrees) to cover an adjacent defect. The flap becomes shorter as it is transposed, so the flap must be developed longer than the defect. Dog ears tend to develop as well. This flap works best when developed directly adjacent to the defect and is useful around the face and rump, but needs to be carefully planned and measured.

Single Pedicle Advancement Flap

This is a flap of skin that is mobilised by undermining and then advanced into a defect, taking advantage of the elasticity of skin. The flap should be at least as long as the defect - the longer the flap the less the tension on the suture line - but usually not more than twice the width. Dog ears adjacent to the base of the flap can be excised after flap advancement and try to make the base wider to optimise blood supply to the leading edge of the flap. Large flaps may require a drain.

H-Plasty

An H-plasty is simply made up from two opposing single pedicle advancement flaps. This technique can be useful in chronic wounds where the adjacent skin is less elastic due to fibrosis.

Skin Fold Flaps

The elbow fold flap and flank fold flap utilise the folds of skin from the elbow to the trunk, and from the hindleg to the trunk. A fold can be developed into a flap by retaining just one of the four possible pedicles: medial or lateral leg, dorsal or ventral trunk. Once conceptualised, these flaps are robust and versatile, and can be used to reconstruct wounds on both the trunk and proximal extremities (Figure 1).

Figure 1. Diagram illustrating the pedicles of the flank fold flaps.

Axial Pattern Flaps

Axial pattern flaps enable the surgeon to transfer skin areas of considerable dimensions in a single stage safely without the necessity of a delay procedure. The commonest cutaneous arteries of the dog and cat used for axial pattern flap development are listed below, and we will go on to detail two flaps that are very robust and have consistent pedicles (Figure 2).

 Thoracodorsal axial pattern flap development. The cutaneous branch of the thoracodorsal artery and vein arise from the caudal shoulder depression. The cranial border is defined by the spine of the scapula, and the caudal border by a parallel line twice the distance from the cranial border to the shoulder depression. The dorsal border of the flap can be an L shape (hockey stick configuration), or straight (peninsular configuration), and typically extends no more than halfway down to the contralateral pedicle. Dissection should proceed deep to the cutaneous trunci muscle and the vascular pedicle should always be identified. Once elevated, this flap can be islanded or maintained with a cutaneous pedicle ventrad. The ventral border of the flap (if being islanded) is drawn at approximately the level of the shoulder joint. The thoracodorsal axial pattern flap can be used to cover large defects of forelimb (almost down to the carpus), axilla, elbow, sternum, shoulder and lateral neck. Animals with large amounts of subcutaneous fat can experience partial flap necrosis distally.

 Caudal superficial epigastric (CSE) axial pattern flap development. These flaps are also robust and have an extremely anatomically consistent vascular pedicle - the caudal superficial epigastric artery (and vein) which arise from the pudendal vessels as it exits the body through the inguinal canal. This is a long flap that will contain the caudal three or four mammary glands, depending on the size required. The medial landmark for this flap is the ventral midline; the lateral border is twice the distance from the midline to the nipple line. These medial and lateral incisions can be joined with a curved transverse incision cranially behind the first or second mammary gland. The flap is undermined down to the body wall and the vascular pedicle should always be identified. To island the flap, a transverse incision is made at the level of the cranial pubis. The CSE flap can be swung around to cover defects of medial and lateral thigh and stifle, caudal abdomen, prepuce and perineum. It is reliable and cosmetically acceptable in ovariectomised animals.

Figure 2. Diagram illustrating the major direct cutaneous arteries that are used in the development of axial pattern flaps. Numbers refer to the list above. 1 = Superficial temporal; 2 = Caudal auricular; 3 = Orbicularis oris (complex facial); 4 = Superficial cervical branch of the omocervical; 5 = Superficial brachial artery; 6 = Thoracodorsal; 7 = Cranial superficial epigastric; 8 = Caudal superficial epigastric; 9 = Deep circumflex iliac artery; 10 = Genicular branch of the saphenous artery; 11 = Reverse saphenous conduit flap; 12 = Superficial lateral caudal.

General Guidelines for Axial Pattern Flap Development

Read the landmarks for borders. Careful positioning is required to prevent distortion of anatomical landmarks and ensure inclusion of direct cutaneous artery. As such large flaps can be developed, the patient may require repositioning once the flap is developed. Flaps can be rotated adjacent to the donor site, taken to a distant site via a bridging incision or tubing of the flap.

Planning Your Reconstructive Surgery

 Manage the wound to a point where it is ready for a reconstructive effort, e.g., healthy wound and periwound area

 Consider all alternatives of closure

 Consider staging the reconstruction? Or partial closure?

 Consider host factors, e.g., geriatric, renal, hepatic disease, Cushingoid, etc

 Consider patient comfort and ability to tolerate the procedure

 Consider owner commitment and likelihood of compliance

 Consider potential stresses (tension, movement) on the area, and the usual activity level of the patient

 Know the vascular supply to the area

 Imagine it, play with the periwound, manipulate the wound edges

Flap Development

 Generous clip, then clip more - free drape leg

 Manipulate the wound edges again, confirm plan and alternative plan

 Anticipate location of drains

 Consider donor site closure

 Use sterile marking pen

 Undermine the panniculus layer (preserving any direct cutaneous vessels)

 Atraumatic technique

 Avoid backcuts into flap

 Minimal tension - approximate edges and 'negotiate' the flap

 Generally perform a two-layer closure: subcutaneous layer, skin

References

1.  Hunt GB, Tisdall PL, et al. Skin-fold advancement flaps for closing large proximal limb and trunk defects in dogs and cats. Veterinary Surgery. 2001;30:440–448.

2.  Hunt GB. Skin fold advancement flaps for closing large sternal and inguinal wounds in cats and dogs. Veterinary Surgery. 1995;24:172–175.

3.  Pavletic MM. Atlas of Small Animal Reconstructive Surgery. 2nd ed. Philadelphia: Saunders. 1999.

4.  Swaim SF, Henderson RA. Small Animal Wound Management. 2nd ed. Baltimore: Williams & Wilkins. 1997.