SKIN FLAP

A portion of skin and subcutaneous tissue and, when possible, the underlying fascia (the thin layer of connective tissue overlying muscle that has an excellent vascular supply) is moved to fill the defect. This movement of tissue results in a new defect at the donor site. Often the donor site can be closed primarily, but sometimes a skin graft is needed.

Classification

Skin flaps are classified as either axial or random. The classification is based on the blood supply.

Axial Flaps

The circulation of an axial flap is supplied by specific, identifiable blood vessels. Careful anatomic study has identified several donor sites with a single artery and vein responsible for circulation to a particular area of skin. Examples include the volar forearm skin supplied by the radial artery and skin on the back supplied by the circumflex scapular artery (a branch of the thoracodorsal artery).

Circulation based on specific vessels results in a highly reliable blood supply and a reliable flap. You can be confident that unless there is an injury to the vessels, the majority of the flap tissue should survive in its new position.

Axial flap. Note that the blood supply comes from an identifiable vessel. As a result, the pedicle can be quite thin, which makes transferring the flap to its new site an easier task.

An axial flap can be completely detached from all surrounding tissue as long as it remains connected to its supplying blood vessels. These vessels serve as the pedicle. The thin pedicle allows axial flaps to be easily positioned to fill the wound defect (unlike the random flap).

The difficulty with an axial flap is locating the blood vessels. You must be very careful not to injure the vessels when creating the flap. The necessary technical expertise is beyond the realm of most providers without reconstructive surgical training. Thus, no specific axial skin flaps are discussed in this chapter.

Random Flaps

Circulation to a random flap is provided in a diffuse fashion through tiny vascular connections from the pedicle into the flap. The pedicle must be bulky to increase the number of vascular connections. The more vascular connections, the better the circulation to the flap. The better the circulation to the flap, the better its survival.

In general, a random flap does not have as reliable a blood supply as an axial flap. Nonetheless, the relative ease of creating random flaps makes them useful almost anywhere on the body. The circulation and thus the reliability of the flap can be increased by “delaying” the flap before final transfer.

Delay Procedure

Before the flap is created, the tissue gets its blood supply via all of the surrounding skin and underlying tissue attachments. When the flap is created, the circulation to the flap comes only from the pedicle.

The purpose of the delay procedure is to enable the pedicle to assume its role as the main source of circulation before the flap is moved to its new position. This goal is obtained by making some of the incisions needed to create the flap but not separating the flap from the underlying tissues. The flap is not moved to its new position; instead, the skin edges are sutured together loosely.

The total blood supplied to the flap initially decreases when the incisions are made. This decrease promotes opening of new vascular channels between the pedicle and flap. Thus, more blood will flow into the flap through the pedicle than if the delay procedure had not been done.

Delaying the flap before final transfer allows more confidence in the viability of the flap. Wait about 7–10 days after the delay procedure before moving the flap to the recipient site.