Considerations in Wound Closure

The management of large wounds or those in challenging locations has received much attention in the veterinary literature over the years and have been the subject of many research efforts to find innovative new ways to manage these often challenging situations. With so many different options for closure available, it can be confusing to know which technique or combination of techniques to use to maximize the chance of achieving a good outcome. In this presentation an attempt will be made to offer solutions to some examples of challenging wounds that are commonly encountered in veterinary practice with local skin flap techniques that do not necessarily demand specialist training or equipment.

Decision-Making

In general, the surgeon should always choose the simplest modality for wound closure that is likely to yield a successful outcome. Many different factors come into play when deciding what technique to use to close a wound. In oncological procedures that require large tissue excisions, certain principles must be adhered to; a larger area of tissue should not be contaminated with neoplastic cells by the use of elaborate flaps if a more simple closure could be successful. Failure to adhere to these principles can make subsequent management with further surgery or adjunctive radiation therapy in the event of an incomplete excision, more challenging.

The use of drains in oncological excisions is similarly controversial given the possibility that the drain tract could be seeded with neoplastic cells. Careful use of drains is generally considered reasonable in these

situations but drains should always exit adjacent to the primary incision and in an area where complete excision or radiation treatment of the drain tract is possible.

The level of wound contamination is an important factor to consider. Closure of contaminated or dirty wounds is discouraged whether primary closure or a skin flap is planned. The most common contaminated wounds encountered are traumatic (especially degloving injuries) in origin or the result of post-operative wound infections. These wounds are managed open until a healthy granulating bed has formed at which point decisions can be made as to whether closure is reasonable and if so whether any kind of skin flap is necessary.

Many factors both related to the local wound environment as well as systemic or other exogenous influences affect the ability of wounds to close and may influence the reconstructive techniques chosen. Local wound factors such as oxygen tension, blood supply and presence of necrotic or foreign material must be taken into account. Exogenous factors such as systemic disease, corticosteroids, cytotoxic drug use and radiation therapy can have profound effects on normal wound healing.

These factors may necessitate the use of techniques that improve blood supply. This could include excision of a pre-existing old granulation bed that no longer has a good blood supply and waiting for a new granulation bed to form that has improved vascularity. Another example might be the choice of a well-vascularized skin flap over a skin graft for reconstruction of a poorly-vascularized radiation ulcer.

Vascular Supply to the Skin

A knowledge of the blood supply to the skin is important when considering any kind of reconstructive surgery for wound closure. If inappropriately handled local flaps may suffer vascular compromise, which may lead to necrosis. Direct cutaneous arteries and veins supply the subdermal plexus in dogs and cats. The subdermal plexus lies above and below the panniculus muscle in areas where this muscle is present, which includes most of the head, neck, trunk and abdomen. In the middle and lower parts of the limbs where there is no panniculus muscle present, the subdermal plexus lies in the deep areolar tissue on the deep face of the dermis. It is vital whenever skin is being undermined for primary closure, or elevated for flap development, to dissect in the plane below the subdermal plexus and to avoid any damage to the vascular pedicles of the direct cutaneous arteries. The course of many of the direct cutaneous arteries have been documented in dogs and cats and can be found in most of the surgical texts.¹

Local Flaps

Many different types of local flaps exist. All rely on the availability of readily moveable skin located adjacent to the wound. Local flaps transfer full thickness skin along with varying degrees of the underlying subcutaneous tissue and have the advantage of providing padding and a fairly reliable blood supply.

Local flaps obtain blood supply through the subdermal plexus without known inclusion of a direct cutaneous artery and vein. These flaps can be transposed, rotated or advanced into the wound depending on where the supply of loose skin for closure is located relative to the wound. Unfortunately, there is no direct relationship between flap width and length that guarantees an adequate vascular supply to local flaps and so it is difficult to give exact rules regarding how wide the pedicle should be.

As wide a base as possible should be used as this will increase the likelihood of incorporating more direct cutaneous vessels. A loose rule of thumb is to ensure that flap length is no more than twice the width of the base.

One type of local flap that we have used extensively are the skin fold advancement flaps.² These flaps take advantage of the abundance of loose skin available in the axillary and inguinal regions. These folds of skin have a medial and lateral attachment to the upper limb and dorsal and ventral attachments to the trunk. Any three of these four attachments can be elevated resulting in a surprisingly large amount of skin that can be rotated into defects of the medial or lateral limb or areas on the trunk or lower abdomen depending on whether the axillary or inguinal folds have been used. They are extremely versatile and can also be elevated bilaterally for closure of large wounds on the ventrum. It has been suggested that in some cases the axillary skin fold is actually an axial pattern flap based on the angiosome of the lateral thoracic artery.^2,3

Other very user-friendly and simple flaps include the single pedicle advancement flap, the transposition flap and rotational flap. The anatomy of these flaps and areas where the author has found these flaps useful will be discussed in this lecture using case examples in each case.

References

1.  Pavletic MM. Atlas of Small Animal Wound Management and Reconstructive Surgery (3rded). Wiley-Blackwell, 2010.

2.  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.

3.  Andersen DM, Charlesworth TC, White RAS. A novel axial pattern flap skin flap based on the lateral thoracic artery in the dog. Vet Comp Orthop Traumatol 2004;17:73–7.