Several options are available to the dermatologic surgeon for the closure of surgical defects. The options range from simple side-to-side closure to more complex closures that use skin flaps and grafts. The choice of closure technique depends on the patient, the type of tumor, the location of the wound, and the local tissue characteristics and availability. Indications, techniques, and complications of advancement flaps are discussed in this article.
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Choosing a repair technique
The first issues to address when choosing a reconstructive approach are to decide if a skin flap has any advantages over a side-to-side closure and to consider other closure options, such as secondary intention healing or skin grafting.
The advantage of a side-to-side closure is that it results in a straight or slightly curved line with little risk of complications, such as necrosis. Secondary intention healing may be the best option for concave areas of the face (eg, conchal bowl, alar groove or rim, melolabial fold, preauricular area, medial canthus), where it can provide an excellent cosmetic result. However, a flap should be considered if excessive tension or anatomical distortion is present or if cosmetic units or relaxed skin tension lines will be breached by a fusiform closure. If tissue movement is insufficient for a flap, a graft may be required. The best tissue match is often obtained with a full-thickness skin graft; however, poorly vascularized areas may only support a split-thickness skin graft. Wounds that involve exposed bone, cartilage, or tendon or wounds in poorly vascularized areas that cannot support grafts may require a flap.
The second issues are the location of potential donor skin and the availability of enough tissue. Locating and assessing donor skin can be accomplished by gently pinching tissue in multiple directions around the defect. Reservoirs of excess tissue include the glabella, the nasal sidewall, and the medial part of the cheek for nasal defects; the temple and the glabella for forehead defects; and the melolabial fold and the cheek for upper lip defects.
General principles of tissue movement
The next decision is to choose the mechanism by which tissue may be moved. Advancement, rotation, and transposition flaps should all be considered. The effect on surrounding structures must be evaluated; in particular, check for any distortion of free margins. A basic knowledge of the terminology of flap dynamics is essential.
Primary motion is movement of the flap into the surgical or primary defect. The defect created by the flap movement creates a secondary defect. The objective of any flap is to close the primary defect, while minimizing the size of the secondary defect.
Secondary motion consists of the elastic forces attempting to return tissue that has been advanced back to its natural position. Secondary motion includes the response of the surrounding tissue to the motion of the flap and to the closure of the primary and secondary defects. The effects of these forces are determined by testing the laxity of the skin under consideration by pressing and stretching the tissue before anesthetic is injected. Undermining the area around the surgical defect may help better define the forces of tension.
Free margins and anatomical units should always be evaluated for possible distortion. Examples of such tests include the snap test on the lower eyelid, which checks for the creation of ectropion. Another test is the application of upward and inward pressure on the nasal bridge (or nose) to determine the potential for elevation of the alar rim.
Finally, the surgeon must determine whether tissue can be moved in a manner that hides the final scars. Scar camouflage is a major advantage of flaps. Suture lines can be placed in facial unit junction lines or in relaxed skin tension lines; such placement often results in barely perceptible scars.
Three types of cutaneous flaps are used: advancement, rotation, and transposition. The focus of this article is advancement flaps. In advancement flaps, the primary motion is in a straight line from the donor site to the primary defect, while the secondary motion occurs in the opposite direction. These flaps are best used in areas of tissue redundancy.
The primary goal of an advancement flap is to transfer the tension of the scar that would result from side-to-side closure to a more cosmetically acceptable site. Such sites include relaxed skin tension lines and the boundaries between cosmetic units (eg, melolabial fold, melolabial crease). Dog ear correction scars are displaced from the original defect, and they can also be hidden in cosmetic boundaries or in skin lines.
Mechanics of advancement flaps
The width of any flap is proportional to the width of the defect. The pedicle or base of the flap connects it to the surrounding tissue. The pedicle contains the flap's vascular supply; thus, it is critical to its survival. The location of the pedicle base in relation to the distal aspect of the flap is often used to describe the flap; flaps are superiorly, inferiorly, medially, or laterally based.
To ensure that the pedicle provides adequate blood flow, the length-to-width ratio of the flap should not usually exceed 3:1. The thickness of the flap should be proportional to the depth of the defect, and the flap must comprise at least a thin layer of subdermal fat to include part of the vasculature. Thinning of the distal flap edge to improve wound contour is common; however, thinning should be avoided in patients with a tenuous blood supply, such as those with diabetes or those who smoke.
Longer flaps should be thicker, especially at their base, to include the larger-caliber deep subcutaneous vessels needed to nourish the entire length of the flap. Exceptions to this principle are well-vascularized areas, such as the nasal dorsum or the helix of the ear.
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Advancement flaps are not indicated for defects in which side-to-side closure is difficult and structural distortion is likely. The exception is a mobile structure, such as the lip. In this situation, a dog ear can be positioned away from the original wound, creating a tension-free closure. Closing the displaced dog ear advances the flap toward the defect, while relieving tension on the flap and the mobile structure. Limiting tension on the defect is imperative for avoiding structural distortion.
Advancement flaps are appropriate for tumors excised with adequate margins or via Mohs surgery, which minimizes the risk of recurrence. If the surgical margins are inadequate and the defect is repaired with a flap, detecting a recurrence may be more difficult, and reexcision of the recurrent tumor may be extensive and disfiguring.