Bryden J. Stanley, BVMS, MACVSc, MVetSc, DACVS
There are often several options for managing wounds and cutaneous defects successfully. Our aim is to restore pain-free function rapidly with the best cosmetic results, at a reasonable cost to the owner. Wounds in small animals often heal completely by second intention due to excellent contraction in these species. However, if a defect is large or subject to repetitive trauma, second intention healing may be cosmetically and/or functionally inferior to a reconstructive procedure. Deciding when to close a wound is based on several factors affecting the wound, including degree of contamination, extent of soft tissue injury/ischemia, time since injury, potential for dead space, certain aetiologies, host status, and client/patient considerations. Timing of wound closure is classified as:
1. Primary closure = immediate closure of wound
2. Delayed primary closure = closure before granulation tissue appears in the wound
3. Secondary closure = closure when granulation tissue is present
4. Second intention healing = heals only by fibroplasia, epithelialization and contraction
Reconstructive techniques can be employed at any point in the wound management process (primary, delayed primary or secondary closure). If there is uncertainty as to whether a wound is ready for closure, then it is generally prudent to manage open until the decision is clear.
Skin is not equally pliable in different directions. Tension lines in the skin are formed by the predominant pull of the fibrous tissue within the skin. There is general agreement regarding the main direction of tension lines in the skin but there are breed, sex and age variations. In breeds with minimal skin laxity, tension lines should be seriously considered. Closing the wound parallel to tension lines generally places less tension on the sutures, minimises puckers or "dog ears", and reduces the incidence of a "biologic tourniquet". Manipulating the edges of the wound, and estimating if the tension is within physiological limits will facilitate decision-making. No wound should be closed by simple approximation of wound edges if the resulting tension will lead to ischemia and subsequent necrosis of the tissue. Tension relieving techniques allow local tissues to be moved to cover a cutaneous defect. Methods for relieving tension on a primary suture line include mobilizing local tissue by undermining, tension relieving sutures, relaxing incisions, and skin stretching.
Undermining allows the full elastic potential of the skin to be utilised to cover a wound, but it increases potential for dead space, so should be used only as much as necessary. Undermining should be deep to the panniculus carnosus muscle when present, to preserve the deep subdermal plexus. The surgeon should also try to preserve any direct cutaneous vessels.
A variety of sutures aimed at spreading the tension within the skin over a larger area have been described, thus minimising 'pull out' of the skin sutures from pressure necrosis. Some common techniques include: Walking sutures, stent sutures, strong subcutaneous sutures, and far-near-near-far or far-far-near-near sutures.
Commonly used relaxing incisions include a simple relaxing incision, mesh expansion, and VY plasty. A simple relaxing incision is useful for closing defects near an orifice, to prevent distortion of the opening. It can also be used when tissue adjacent to the defect chronically scarred, but nearby tissue has normal elasticity. Mesh expansion, or multiple punctate relaxing incisions are small, parallel, staggered incisions made in the skin adjacent to the wound to relieve the tension. A V-Y plasty is indicated for closing defects that are chronic and surrounded by inelastic skin, and closing wounds near structures that would be distorted by closure under tension.
Several suturing techniques take advantage of the mechanical creep ability of the skin. Presuturing of the skin adjacent to the wound will relax the collagen and elastin fibers over 24 hours, and facilitate definitive wound closure. Adjustable continuous intradermal suturing will also provide stress relaxation and eventually biological creep to provide adequate cutaneous coverage without tension. Skin expanders can also be used.
These are just a few of the plastic procedures that can be used for relieving tension on the primary suture line.
Cutaneous Pedicle Grafts (Skin Flaps)
A skin flap is portion of skin moved from one area of the body to another with an intact vascular attachment to its donor site. Properly developed flaps survive because of their intact circulation. The loose, elastic skin over the head, neck and trunk in dogs & cats, plus the presence of direct cutaneous arteries make pedicle grafts common and successful in practice. Flaps are indicated in the presence of large cutaneous defects in areas where local tissues cannot be mobilised. They are very versatile and capable of improving regional circulation to an area, covering areas that are difficult to immobilise, providing immediate padding and protection, and they provide a hirsute skin surface.
Subdermal plexus flaps (random flaps)are elevated without inclusion of direct cutaneous vessels and rely on perfusion via the subdermal plexus. They are classified as follows:
Single pedicle advancement
Bipedicle advancement flap
Hinge (single pedicle)
Some useful subdermal plexus flaps are described below.
Rotation Flap: A semicircular flap of skin that rotates about a pivot point across a triangular defect. The arc should be long enough to create a flap that has no tension on it when sutured into place: at least 4x the distance through which the flap is to be moved. The flap can be created progressively, undermining until adequate skin is available to cover the defect.
Single Pedicle Advancement Flap: A flap of skin that is mobilised by undermining and then advanced into a defect, taking advantage of 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 2x the width. 'Dog ears' adjacent to the base of the flap can be excised after flap advancement.
H-Plasty: Is simply made up from two apposing single pedicle advancement flaps. This technique can be useful in chronic wounds where the adjacent skin is less elastic due to fibrosis.
Pouch Flap: A bipedicle flap is created on the body to reconstruct a defect on an extremity by temporarily moving the extremity to the flap. It is important to ensure that the animal will tolerate a limb bandaged to the body for 14 days. Note that in hind limb pouch flaps, the hair will grow in a reverse direction. These flaps can benefit from delay procedures, i.e., the pedicles can be cut down in stages. Careful bandaging is required to ensure that the flap is not under tension from the leg, and movement is not excessive.
Length to width ratios for subdermal plexus (random) flaps: generally do not exceed 2:1 for single pedicle flap, or 4:1 for bipedicle flaps.
Skin Fold Advancement Flaps
These flaps (described by Geraldine Hunt), utilise the folds of skin from the elbow to the body, and from the flank. A fold can be developed into a flap by retaining one of the four possible pedicles: medial or lateral leg, dorsal or ventral trunk. The flaps can be used to reconstruct cutaneous defects on both trunk and proximal extremities.
Axial Pattern Flaps
Axial pattern flaps enable the surgeon to transfer considerable dimensions of skin in a single stage. Theyincorporate a specific direct cutaneous artery and vein, using established guidelines for flap development. These flaps have an excellent blood supply and allow large areas of flap mobilization. They have 50% greater survival compared with subdermal plexus flaps of same dimension. Axial pattern flaps are not dependent on their cutaneous base, and island arterial flaps can be created, thus enhancing mobility. Flaps can be rotated adjacent to donor site, or taken to a distant site via a bridging incision or tubing of the flap.
These flaps can also be developed and transferred to a distant site by microvascular anastomosis of the direct cutaneous vessels to a skeletonized and prepared recipient vascular pedicle.
The cutaneous arteries of the dog and cat used for axial pattern flap development are the: superficial temporal (useful for face and muzzle defects); caudal auricular (not that robust); prescapular branch of the superficial cervical artery (formerly the omocervical trunk), arising cranial to the scapula on the side of the neck--variable anatomy; superficial brachial artery (not very robust, but useful for antebrachial defects); thoracodorsal artery (arising just caudal to the scapula, a very large flap); caudal superficial epigastric artery (running cranially up the mammary chain from the inguinal ring); deep circumflex iliac artery (arising just cranial to the wing of the ilium, robust); genicular branch of the saphenous artery (from the lateral thigh, not that robust); and superficial lateral caudal from the tail. The reverse saphenous conduit flap is a variation on an axial pattern flap. A composite axial pattern flap based on the angularis oris has recently been described for restoration of palate defects.
Planning Your Flap
1. Consider all management alternatives, including second intention healing as well as reconstructive techniques. Consider host factors as well as local factors that may affect wound healing.
2. Consider potential stresses such as tension and movement on the area, and the usual activity level of the patient (e.g., cat vs. hunting dog).
3. Consider patient comfort and ability to tolerate the procedure (e.g., distant direct flaps).
4. Ensure that owner will be compliant with instructions and is committed to the plan.
5. Determine the vascular supply to the area.
Flap Selection and Development
1. Manipulate the wound edges to ascertain tension lines. This helps in developing a plan for reconstruction.
2. Two small flaps may be preferable to a single large flap with questionable circulation.
3. Will staging the reconstruction or a delay procedure be advantageous?
4. Determine ideal donor areas and aim for inclusion of a direct cutaneous artery, even if not an axial pattern flap. Can skin folds be utilised?
5. Ensure that the recipient bed is free from gross contamination, infection and necrotic tissue.
6. How will the donor site be closed? Another reconstructive procedure? When?
7. Will drains be required, and what sort of drainage will be best?
8. Use templates or rulers, and a sterile marking pen. Work in reverse.
9. Undermine deep to the dermis, beneath the panniculus layer (preserving any direct cutaneous vessels).
10. Use stay sutures or skin hooks. Avoid backcuts into flap. Place a subcutaneous layer, then skin layer. Place initial 'tacking' sutures to ensure that flap conforms well to the recipient site, with the tension spread evenly.
11. Ensure minimal tension on flap suture lines.
Analgesia is important with all traumatic and surgical wounds. Opioids are excellent, NSAIDs can be used with care (ascertain renal, hepatic function, watch out for GI disturbance). Epidurals and/or a constant rate infusions (CRI) are excellent options for pain control in the early post-wounding or post-operative days. CRIs of fentanyl, or hydromorphone/lidocaine, ketamine/morphine/lidocaine are effective.