G. Dupré, DECVS, Dipl. Human Thoracoscopy and Interventional Pneumology
Clinic for Small Animal Surgery, Veterinary Medicine University of Vienna, Vienna, Austria
- Understand the indications and principles of pouch flaps
- Be able to apply those on clinical patients
The surgeon's choice for skin closure depends on many factors: species, breeds, size and localization of the wound, tissue trauma, contamination, wound healing phase. From these factors the practitioner will have to base his decision on how to close the skin defect:
- With primary, delayed primary, secondary closure or second-intention healing
- With direct apposition, local flaps, distant flaps, or graft
Finally, given the ability of small animals to potentially heal by second intention, many veterinarians spend a lot of time and money in bandaging techniques to cover a wound that has been improperly closed and finally dehisced. The final cosmetic result is often poor and the psychological impact over the client may be disastrous, whereas a correct timing in closure and correct technique would have been possible and would have saved time and money.
A pouch flap is indicated to cover major skin deficits distal to the elbow or to the knee joints. We have used it in many different formats from 1.5-kg Yorkshire to 60-kg bullmastiff. The major advantage is the ability to bring healthy, full-thickness skin (and subcutis) to cover a large skin deficit. The major disadvantage is the position in which the limb has to be brought to for at least 10 days before the flap is actually cut and brought to the recipient bed.
A successful outcome of a skin reconstruction surgery depends on careful preoperative planning and accurate application of the chosen technique in order to prevent circulatory compromise and extensive tension. For both these issues, a sound knowledge of surgical anatomy and of the skin blood supply is essential. In dogs and cats, the latter is mainly warranted by the direct cutaneous arteries and veins. They arise from the level of skeletal musculature and run parallel to the skin. The cutaneous vascular system is further divided into:
- The deep (subdermal or subcutaneous) plexus, being directly supplied by the direct cutaneous vessels. It lies superficial and deep to the panniculus muscle or in the deep layers of the hypodermis where no panniculus muscle is present. The deep plexus directly supplies the hair bulb and follicle as well as the arrector pili muscle and gives branches to
- The middle (cutaneous) plexus which is located in the deeper layers of the dermis. It supplies the sebaceous glands and reinforces the capillary network around the hair follicles and glandular ducts. Its branches ascend to supply
- The superficial plexus that lies in the outer layer of the dermis. Capillary loops of this plexus project into the dermal capillary bodies to supply the epidermal papillae and adjacent epidermis.
By far the most important anatomic consideration during surgical procedures is the cutaneous circulation. Survival of skin flaps relies mostly on the preserved skin circulation. The deep or subdermal plexus is the most important anatomical feature of the skin circulation in dogs and cats and it must be preserved when undermining the skin. The vessels of the subdermal plexus run parallel to the skin in the subcutaneous tissue and provide most of the vascular supply of the skin. On fresh wound, reconstruction can be done readily. In all other cases, the surgeon must wait for a nice uncontaminated wound, and, in most cases, for a granulated bed. Use of a pouch flap after tumor removal shall be questioned because of the risk of tumor cell seeding. At the time of surgery, the granulation bed can be left in place or partially or totally excised at the time of final closure. We usually trim the edges of the granulation bed to obtain a nice skin apposition.
By definition a pouch flap is a direct distant bipedicular flap (the donor bed being located at a distance of the recipient bed).
The vascular supply of a pouch flap comes from the pedicles of the donor area and to some degree from the recipient bed (when it is a granulation tissue). The surgical treatment always follows the same steps:
- Tolerance's test: Before the tunnel is created, the tolerance of the patient is tested by bringing the leg into position for at least 24 hours without performing the actual surgery. Should the patient not tolerate the position, a pouch flap should be discouraged and another technique should be considered.
- Preparation of the recipient bed. It can be a fresh or a granulated wound.
- Flap design. The flap is designed over the chest or flank area and two incisions are made perpendicular to the long axis of the body to create the tunnel in which the limb will be slid.
- Position of the limb. Once the limb is positioned into the tunnel, the cranial and caudal incisions are partially closed. No tacking sutures are placed to avoid damage to the underlying blood vessels.
- Flap section. After 10 days to 2 weeks, the dorsal and ventral pedicles are cut and the limb is freed from its attachments. In some occasions the pedicles are cut stepwise within 4 to 6 days.
- Closure. Once the flap has taken over the initial wound, it can be completely closed over the limb.
- Pain control, drainage, and bandages are mandatory to allow a good healing.
Pros and Cons
The main advantage of this technique is an almost 100% "flap take" with a full-thickness skin coverage. The main disadvantage is a staged procedure with 2 major surgeries and the discomfort for the patient having "one leg in the chest." Complications include dehiscence, secondary infection, and ankylosis.
Despite the paucity of literature, pouch flaps have been found to be very useful to cover large distally located limb deficits avoiding the combination of flaps and grafts.