Novel Wound Closure Techniques
The companion animal skin consists of two main layers. The general composition of the outer layer, the epidermis, is of avascular keratinised stratified squamous epithelium. The thicker vascular dermis lies underneath the epidermis and consists of tough fibroelastic tissue with a supportive and nourishing function. The dermis rests on a layer of loose connective tissue known as the subcutis or hypodermis, composed of adipose tissue, the cutaneous trunci muscle (where present) and direct cutaneous arteries and veins. This layer is particularly abundant in most dogs and cats, but the quantity and elasticity of skin differs from breed to breed and on the physical condition of the animal. Variations in structure are present at different sites of the body surface. For instance, the nose has a thick protective keratin layer. In addition, in most skin areas specialized epithelial appendages exist such as hair follicles and sebaceous glands.
In dogs and cats, direct cutaneous arteries are responsible for supplying large areas of skin. They run parallel to the skin in the hypodermis and arise from perforator arteries. Musculocutaneous arteries branch off the perforator arteries and supply small portions of the skin and run perpendicular to the surface of the skin.
The subdermal plexus in dogs and cats is of major importance in companion animal reconstructive skin surgery and should always be preserved when undermining skin for local flaps, especially when no direct superficial arteries can be incorporated in the proposed flap. Axial pattern flaps are flaps based on such direct cutaneous arteries and veins that supply a specific region of dermal tissue. Since the terminal branches of these vessels supply the subdermal plexus, axial pattern flaps have better perfusion than local flaps and are widely used in veterinary reconstructive surgery.
Tension on the wound edges is the most common reason for skin reconstructions to fail and occurs when insufficient skin is available to close the initial defect. The elasticity of the canine and feline skin is primarily the result of the lack of firm attachment of the subcutis to the bone, muscle, and fascia. The skin is loose and abundant on most parts of the body, particularly on the neck and trunk, but is less pliable on the limbs, tail, and head, especially around the bridge of the nose, nasal planum, and medial canthi. This is the result of linear alignment of fibrous tissues within the skin in this area.
The tension lines of the head and neck region resemble the orientation of the underlying muscles. Generally speaking, incisions should always be made parallel to tension lines to minimize wound tension during closure. Incisions that are made in an angle or perpendicular to these lines may result in wound deformation, wound dehiscence, and necrosis. If this is impossible, methods to reduce skin tension should be employed upon closure. These include, from simple to more advanced, undermining the wound edges, selecting tension-relieving suture patterns, using tension-releasing incisions or skin stretching and tissue expansion techniques. If these methods do not allow primary closure of the wound, secondary intention healing or reconstruction with skin flaps or grafts have to be considered.
Reconstruction of the Face
Reconstruction of the facial area can be challenging. There are 3 major reasons for the challenge: 1. skin is less abundant than in other areas of the body, 2. there are major essential structures that make proper reconstruction more difficult and 3. it is an obvious area, i.e., people immediately see if something is not completely right. Specific facial reconstructive techniques include the caudal auricular axial pattern flap, the crescentic nasojugal flap, the facial artery axial pattern flap, and the superficial temporal artery axial pattern flap.
Reconstruction of the Neck and Trunk
Reconstruction of skin defects in the neck area is usually relatively easy in dogs and cats, because of their considerable amount of loose skin in this area. In most cases defects can be closed using local skin flaps. However, after radical resection of tumours, for closure of large traumatic wounds, or for reconstruction in areas with compromised blood supply, other techniques have to be used. The axial pattern flaps that can be used for the reconstruction of large defects in the neck are the omocervical, and in some cases the thoracodorsal axial pattern flaps.
Wound Closure Techniques
Most plastic and reconstructive techniques used in companion animals involve the creation of new surgical wounds. The general surgical principles of using aseptical techniques, proper instruments, and delicate tissue handling while creating a surgical wound apply here as well. In addition, appropriate suture materials and suture techniques have to be used for any type of surgery, but for reconstructive surgery in particular.
Complications in Performing Plastic and Reconstructive Surgery
Complications of wound closure in plastic and reconstructive surgery are similar to those in general soft tissue surgeries and include wound dehiscence, infection, hematoma or seroma formation, and excessive scar formation. Most complications can be avoided by a proper pre-operative planning and skin mobility assessment, by using a meticulous surgical technique and achieving haemostasis. Chances of flap survival will increase if the size and localisation of the wound is suitable for receiving the flap, if the wound is neither contaminated nor infected and if the wound is not older than 4–6 hours. It is also important that the recipient bed for the flap is fully prepared. Another complication that should be avoided is the development of dead space, which can lead to the formation of abscesses, seromas, or hematomas. Formation of dead space can be overcome by placing drains, subcutaneous and walking sutures, and bandages. The authors recommend the use of either passive or active drains whenever possible while taking care not to damage the blood supply at the base of the flap by making exit ports.
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