Introduction
Reconstructive skin techniques that transfer skin from an area of the body with excess skin, to the area with the skin defect, are divided into those involving skin flaps and those involving autogenous skin grafts.1 These techniques are reserved for large wounds and wounds that lie in difficult areas. On the whole, they are more advanced procedures and require a certain level of skill before they are attempted. Skin flaps can bypass many of the problems that occur when wounds are left to heal by second intention. In these instances contraction and epithelialisation may lead to excessive scar tissue formation and even dysfunction of a limb.1,2 Furthermore, the money spent on one surgical procedure may end up costing the client less than they would have spent on extensive bandage changes and hospital revisits.
The skin is composed of an outermost protective layer called the epidermis and a thicker, underlying dermal layer that contains the blood and lymph vessels, as well as hair follicles, nerves and associated glands. The blood supply to the skin is derived from the direct cutaneous blood vessels which feed the subdermal (or deep) plexus. This structure in turn feeds a cutaneous (or middle) and a subpapillary (or superficial) plexus. Mapping the position of these direct cutaneous blood vessels, allows for more advanced techniques involving the harvesting of flaps and grafts, which can aid in the closure of substantially larger defects and defects that lie distant from the donor skin area.1-3
Another basic principle of skin surgery involves an awareness of the position of tension lines caused by the skins inherent elasticity. Tension lines are present within the skin's layers and the directions in which these run needs to be considered before choosing the method of repair that will give the most satisfactory results. Wherever possible, incisions should be made parallel to existing tension lines.4 Consideration of patient positioning considerably influences the amount of skin available for wound closure. Simple techniques that are effective in reducing tension across sutures lines include the use of undermining wound edges, walking sutures, adjustable horizontal mattress sutures, "far-near-near-far" suture patterns, relaxing incisions, stent bandages and stent sutures. Excessive tension in skin defects should be avoided as it may lead to many undesirable complications such as: vascular and lymphatic compromise, delayed wound healing, wound disruption, increased pain, increased infection rates and the increased chance of self-trauma.4
Skin Flap Techniques
The classification of flaps is done according to their blood supply, location and tissue composition. When considering blood supply, flaps may be pedicle flaps, which rely on the blood supply to the subdermal plexus or axial pattern flaps that involve a direct cutaneous artery and vein.5 Location determines whether a flap is local (i.e., adjacent to the recipient bed) or distant from the recipient bed. Local skin flaps are utilized when sufficient skin is available adjacent to the affected area. Distant flaps are used almost exclusively for extremities when a limb containing the defect is moved to the donor site for the flap. This is a slightly more complicated procedure and not nearly as well tolerated by the patient as local flaps. Tissue composition of the flap will determine whether we are dealing with one fascial layer or more, i.e., when muscle is involved we term this a musculocutaneous flap.2
Advancement (or sliding flaps) are harvested parallel to the lines of least tension and are then slid over the adjacent defect. They can be single pedicle, bipedicle, "H-plasty" or "V-Y plasty." Transposition flaps are aligned at 90° parallel to the lines of greatest tension. They are rectangular flaps that are rotated 90° into the adjacent defect. The width of the flap is the same as that of the defect whilst the flap length is the distance from the pivot point to the furthest point of the graft. The last type of pivoting flap is known as a rotation flap and these are semi-circular pieces of skin than are used to close triangular defects.
The "delay phenomenon," is a term used when large flaps are raised in 2 or more stages in order to improve their blood supply prior to transfer.1-3 This technique is used in indirect flaps which is when a tube of tissue is created and allowed to heal for a 2 week interval before being unraveled and resutured into the recipient bed. These are useful when skin needs to be transferred to a distant site, but should only be attempted when no simpler method is possible.
Axial pattern flaps, by definition, include a direct cutaneous artery and vein.4 They have a more reliable blood supply than pedicle flaps and can thus be used to close larger defects. They require careful planning and accurate knowledge of where these direct cutaneous blood vessels lie. They can also be modified into island flaps by severing the cutaneous attachment at its base. This allows rotation of the flap and more versatility.
Skin Grafts
Autogenous skin grafts are segments of skin that are freed from their origin and moved to another area of the body where they heal in place. They may be full thickness (includes epidermis and entire dermis) or partial thickness (epidermis and part of the dermal layer). Free grafts rely on absorption of fluids from beneath the graft, followed by the ingrowth of blood vessels from the healthy granulation bed of the recipient site.5 To ensure that fluid does not collect beneath the graft, expanded mesh grafts are often used in skin reconstruction. The most common causes of failure of free skin grafts are separation of the graft from the bed, movement or infection. For these reasons, the postoperative management of free skin grafts is paramount to their success. In most cases, patients are kept hospitalized with good nursing and bandage management.
Free Punch Grafts
The use of free punch (or seed) grafts is a simple technique that is extremely effective for the reconstruction of smaller defects in irregular areas with little adjacent skin.2,6,7 It does not involve any sophisticated equipment and generally yields a high success rate. The cosmetic appearance is poor because of the irregular hair growth and excessive scarring, but they serve the purpose of providing a functional barrier that is resistant to trauma.
Foot Pad Injuries
The pads consist of a deep cushion of connective tissue covered by a thick protective epidermis. Injuries to the pads pose their own set of complications, as this area constantly bears weight during ambulation and the distribution of forces within the pad means that dehiscence of wounds is a common occurrence.8 Full depth pad lacerations should be closed using absorbable suture material in multiple layers. "Far-near-near-far" suture patterns are recommended in the surface layers to alleviate the tension that occurs here.
In patients where the weight bearing surface has been completely lost, pad transposition procedures are possible. The metacarpal or metatarsal pads can be harvested and advanced to cover the palmer or plantar aspect of the paw.9,10 The "phalangeal fillet technique" is used where the metacarpal or tarsal pad has been damaged and a digit is sacrificed in order to use its digital pad to fill the defect in the main weight-bearing pad.9 Finally a procedure involving the use of free pad grafts has been described. This allows the surgeon to reconstruct a weight-bearing surface in instances where it has been destroyed.8
Postoperative management of pad lacerations and grafts includes meticulous bandage care using splinted bandages to prevent premature weight bearing.
References
1. Hedlund CS. Surgery of the integumentary system. In: Fossum TW, ed. Small Animal Surgery. MO: Elsevier Mosby; 2007:159–259.
2. Pavletic MM. Atlas of Small Animal Reconstructive Surgery. 2nd edition. Philadelphia, PA: WB Saunders; 1999.
3. Pavletic MM. Skin grafting and reconstruction techniques. In: Bojrab MJ, Ellison GW, Slocum B, eds. Current Techniques in Small Animal Surgery. 4th edition. Baltimore, MD: William & Wilkens; 1998:585–639.
4. Johnston DE. Tension relieving techniques. Vet Clin North Am Small Anim Pract. 1990;20:60–67.
5. Pavletic MM. Canine axial pattern flaps. Am J Vet Res. 1981;42:391–406.
6. Shahar R, Shamir MH, Brehm DM, Johnston DE. Free skin grafting for the treatment of distal limb skin defects in cats. J Small Anim Pract. 1999;40:378–382.
7. Hunt GB, et al. Skin fold advancement flaps for closing large proximal limb and trunk defects in dogs and cats. Vet Surg. 2001;30:440–448.
8. Swaim SH. Free segmental pad grafts in dogs. Am J Vet Res. 1992;53:2162–2170.
9. Bradley DM, et al. Autogenous pad grafts for reconstruction of a weight-bearing surface: a case report. J Am Anim Hosp Assoc. 1994;30:533–538.
10. Basher A. Foot injuries in dogs and cats. Comp Cont Educ Pract. 1994;16:1159–1176.