Large Skin Defects in Dogs and Cats Treated With Axial Pattern Flaps (And one case where puppies are nursing from the leg!)

Fig. 1: Diagram of basic steps for caudal superficial epigastric axial pattern skin flap.
From: Birchard SJ, Smeak DD. Selected skin graft and reconstructive techniques. In: Saunders Manual of Small Animal Practice. 3^rd edition, Birchard and Sherding, eds., Elsevier, St. Louis, 2006. Pg 557

Axial pattern flaps are skin flaps that are developed using a major direct cutaneous artery as the primary blood supply.  Considerably more flexibility in the length and mobility of these flaps is possible compared to random skin flaps (e.g., the one used in Hershey; see blog from 2/24/14).  These flaps can be made with long vascular pedicles to transfer skin to more remote areas of the body compared to random flaps.  This is because of preservation of the direct cutaneous artery allowing adequate perfusion of a large area of tissue.  

Axial pattern flaps can be based upon many direct cutaneous arteries, such as the caudal superficial epigastric, cervical cutaneous branch of the omocervical, thoracodorsal, deep circumflex iliac, and the genicular branch of the saphenous artery.  The caudal superficial axial pattern flap is commonly used for large defects of the proximal thigh and flank.  The thoracodorsal axial pattern flap is used for defects of the distal humeral area or elbow. These 2 techniques will be described here.  However, other axial pattern flaps as listed above can be created using similar principles and are described in current veterinary surgical textbooks.

Indications

Indications for axial pattern flaps are similar to random subdermal flaps except that these flaps are used when the skin defect is very large. Large skin defects that occur due to trauma, mass excision, or other etiologies resulting in a loss of skin could benefit from this reconstructive technique. A major direct cutaneous artery and vein must be fairly close to the skin defect for this technique to be indicated.

Surgical Procedures

Caudal Superficial Epigastric Axial Pattern Flap

Use similar preparation and tissue handling principles described for advancement or rotation flaps. Be particularly careful when positioning the patient such that the vascular pedicle will not become distorted before planning your incisions.  Incisions are created as shown in Figure 1.  The mammary chain up to and including the 3^rd gland can be included.  Deeply undermine the flap just superficial to the abdominal fascia. Dissect very carefully around the origin of the direct cutaneous vessel to avoid inadvertent damage to this vessel that is vital to the survival of the flap.  Avoid creating a kink in the base of the flap that could obstruct blood flow. (Fig. 2)

Fig. 2: Caudal superficial epigastric axial pattern flap to close a medial  thigh wound

Drain the dead space if needed with a closed suction drain and suture the flap to the defect as described for the other flap techniques. Close the donor site after closing the flap.

Fig. 3: Healed caudal superficial flap on the stifle of a dog. Note nipples that have been transposed with the flap.

Fig. 4: Caudal superficial axial pattern flap was performed on this in tact female dog that subsequently got pregnant. Puppies are nursing from the transposed mammary glands on the leg. From: Pavletic MM. Axial pattern flaps in small animal practice. Vet Clin North Am Small Anim Pract. 1990 Jan;20(1):105-25.

Thoracodorsal Axial Pattern Flap

Fig. 5: Diagram of basic steps for thoracodorsal axial pattern flap.
From: Birchard SJ, Smeak DD. Selected skin graft and reconstructive techniques. In: Saunders Manual of Small Animal Practice. 3^rd edition, Birchard and Sherding, eds., Elsevier, St. Louis, 2006. Pg 557

A rectangular flap of skin is created based on the thoracodorsal artery (Fig. 6) 

Fig. 6: Thoracodorsal flap planned for this non-healing wound secondary to tumor removal followed by radiation therapy. Four previous attempts to close thewound had been performed. 
Lines indicate proposed incisions; X marks the origin of the thoracodorsal artery.

The flap is undermined deep to the cutaneous trunci muscle and rotated to cover the defect. A bridging incision is made if necessary to allow suturing the flap to the skin proximal to the defect. The flap is rotated to the defect and sutured in place. (Fig. 7)

Fig. 7: Same dog as figure 5 with completed flap

Fig. 8: Same dog as figure 5, 2 weeks postoperatively

Care and Complications (All flap types)

Restrict exercise until suture removal. Apply an Elizabethan collar before the patient is recovered from anesthesia and leave on the animal until the flaps are completely healed. Place a well-padded bandage on the front leg after thoracodorsal flaps are used to cover the elbow. Pressure necrosis of the potion of flap directly over the elbow can occur if not protected and cushioned. Change wound dressings as necessary.

Major complications resulting from skin flaps include local wound problems such as:  partial or total ischemia of the flap, infection, seroma, and dehiscence of the flap or donor suture line. Mild bruising of the flap for the first few days postoperatively is expected. Severe discoloration with a sharp demarcation between normal and abnormal skin is likely indicating flap ischemia and impending necrosis. Dehiscence of donor site incisions is usually due to excessive skin tension.  If dehiscence occurs, allow these areas to heal by second intention.

References

1. Birchard SJ, Smeak DD. Selected skin graft and reconstructive techniques. In: Saunders Manual of Small Animal Practice. third edition, Birchard and Sherding, eds., Elsevier, St. Louis, 2006. Pg 557
2.  Aper R1, Smeak DD. Complications and outcome after thoracodorsal axial pattern flap reconstruction of forelimb skin defects in 10 dogs, 1989-2001. Vet Surg. 2003 Jul-Aug;32(4):378-84.
3. Aper RL1, Smeak DD.Clinical evaluation of caudal superficial epigastric axial pattern flap reconstruction of skin defects in 10 dogs(1989-2001). J Am Anim Hosp Assoc. 2005 May-Jun;41(3):185-92.
4. Pavletic MM. Axial pattern flaps in small animal practice. Vet Clin North Am Small Anim Pract. 1990 Jan;20(1):105-25.