Flap Classification and Local Facial Flaps

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Robert W. Dolan

Lahey Clinic Medical Center, Burlington, Massachusetts, U.S.A.

FLAP CLASSIFICATION AND VASCULARITY

Flap classification is based on an evolving paradigm as new uses and new flaps are discovered. The earliest report of a facial flap (the midline forehead flap) is found in the Sushruta Samhita, a Hindu holy book, in 600 bce (1). Flap development was largely ignored or relegated to the unholy in the period between the emergence of Buddhism in India to the 16th century (2). In the 1500s, Tagliacozzi perfected the arm-pedicled technique of nasal reconstruction that became known as the Italian method. The Hindu method was introduced to English speaking society by "B.L." in a letter to the Gentleman's Magazine in London in 1794 (3). This spawned a new era and signaled the rebirth of reconstructive surgery (4).

Flaps for facial reconstruction can be classified into three general categories: local, regional, and distant (free). A local flap is adjacent to the defect, a regional flap is remote (off the face) from the defect, and a distant flap is a flap whose pedicle is completely detached for transfer as a free flap or (rarely) what is termed a walking flap. Further subclassification is based on the nature of the arterial supply to the flap, and, in the case of local facial flaps, the type of tissue movement (e.g., interpolation or advancement). The type of arterial supply varies according to the configuration of the deep-fascia-skin vascular network.

Manchot (1889) (5) introduced the concept that cutaneous arteries have definite vascular territories. Segmental arteries penetrate muscle (musculocutaneous perforators) or bypass the muscular tissue via intermuscular septa [septo/ fasciocutaneous perforators (Fig. 1)] and arborize extensively in several distinct cutaneous and subcutaneous plexuses. The plexuses represent the major blood supply to -g the skin and form in several distinct planes comprising the subfascial, prefascial, sub- |

cutaneous, subdermal, dermal, and subepidermal plexuses (Fig. 2). The subepider- £

mal plexus serves primarily a nutritive role while the dermal plexus serves a thermoregulatory role. The subdermal plexus is the primary blood supply to the skin and is responsible for the bleeding noted clinically at a flap or laceration's edge (6). a

The subcutaneous plexus is better developed on the torso and enhanced flap survival may be achieved when this plexus is included in the flap design (e.g., the deltopec- &

toral flap). The orientation of these vascular territories in the subcutaneous and deep |

fascial planes form the basis of many of the subsequent so-called axial flaps ?

Harvesting Fibula
Figure 1 Lateral skin island reflected anteriorly during harvest of a fibular free flap. Note the septocutaneous perforators (arrows).

described in the latter half of the 20th century. McGregor et al. (1973) further defined the terms axial and random in their analysis of the system of arteries in the deltopectoral and groin flaps (7). An axial pattern flap is a single-pedicled flap that has an anatomically recognized arteriovenous system running along its long axis; a random pattern flap lacks any significant bias in its vascular pattern. Flaps with an axial pattern, with or without inclusion of the deep fascial plexus, can have significantly greater length-to-width ratios than a random pattern flap.

Classification Fasciocutaneous Flaps
Figure 2 The cutaneous vascular plexuses.

The deep fascial plexus is a newly recognized important component of blood supply to the skin in areas of the body where this fascial network is well developed. This plexus tends to be well developed in the extremities and around the shoulders. Fasciocutaneous flaps from these areas depend upon the axial vascular network coursing within the deep fascial plexus for survival (e.g., the parascapular flap). The source arteries reach the deep fascial plexus via septocutaneous segmental arteries and an axial vascular network is then formed at the deep fascial level. There are two components to the deep fascial plexus: the subfascial plexus and the prefas-cial plexus. The axial vascular network is mainly concentrated in the prefascial plexus.

A random pattern skin flap may include tissue from the subdermis through the deep fascia. Random skin flaps are the first to be described in detail in the 20th century along with the "rule of ratios'' that dictates safe length-to-width ratios based on clinical observations of survival. The ratios range from less than 1:1 for extremity skin flaps to up to 5:1 for flaps on the face. The extended ratios for many facial flaps may actually be an indication of their axial subcutaneous vascular patterns from terminal musculocutaneous vessels (e.g., nasolabial flap) and may be more properly classified as axial skin flaps.

LOCAL FLAPS OVERVIEW

It is helpful to subclassify local flaps based on the type of tissue movement involved in transferring the flap from the donor site to the recipient site (8). The two basic classes of flaps are sliding and lifting. Sliding flaps move tissue by direct advancement, leaving a donor defect adjacent to the newly covered recipient site that is of unequal length and is closed primarily. Included in this class are the subcutaneous pedicle/advancement flaps (cheek, V-Y, island pedicled, O-T/A-T plasty); and rotation flaps (dorsal nasal). Lifting flaps cross normal issue to reach the recipient site and include transposition flaps (bilobe and rhombic flaps); and interpolation flaps (melolabial, midline forehead). A transposition flap is adjacent to the defect and transfers tissue in one stage. An interpolation flap is remote from the defect and transfers tissue in two stages: the second stage is for sectioning of the pedicle after an appropriate period of time (usually 2-3 weeks).

There are several local cutaneous flaps described for limited defects on the face. It is helpful to consider the following in preoperative planning:

1. The desires of the patient: Does the patient value cosmesis over the -g expediency of a skin graft or healing by secondary intention? I

2. Medical comorbidities: Is there a history of radiation therapy, tobacco use, » or insulin-dependent diabetes mellitus? All these factors increase the likelihood of ischemic flap loss.

3. Is a skin graft capable of obtaining similar or better results than tissue transposition or advancement? In general, concave areas such as the medial canthal areas and nasal sidewall subunits do very well with full-thickness skin grafts.

4. Is primary closure possible without undue tension or disfigurement? @

BASIC LOCAL FLAPS

Some local flaps involve fundamental soft tissue movement and can be considered for general use depending upon the surrounding characteristics of the skin. After skin grafting, these basic local flaps should be considered before more complicated or staged procedures. The basic local flaps include the single/bilateral pedicle advancement (U-plasty/H-plasty), island subcutaneous V-Y advancement, O-T/A-T plasty, rotation, banner, bilobe, and rhombic. If a basic local flap is planned, there is a step-by-step method described by Calhoun et al. (9) to aid in the conceptualization of the process of flap selection. First, the characteristics of the defect are noted including its size, shape, and location. Good and bad lender units adjacent to the defect are outlined. Good lender units supply adjacent tissues with little distortion or tension of surrounding structures that are distortable such as the eye or lip. Second, the characteristics of each available flap must be considered, including:

The amount of skin undermining required for tissue movement expressed in diameters of the defect size: if a defect is 2 cm in diameter, an A-T plasty requires two times the defects diameter (2D or 4 cm) of adjacent tissue undermining for adequate advancement. Diameter ratios are listed for the flaps discussed by Calhoun including the rhomboid, bilobed, subcuta-neously pedicled, V-Y, and A-T plasty.

The arc (in degrees, 90-360) of territory required for skin undermining: the diameters of skin undermining and the arc describe the surface area and direction of dissection required for each flap.

The vector of maximum tension after flap inset: this is important in determining if structures in line with the tension vector may be distorted. Final scar orientation with respect to the resting skin tension lines (RSTLs): although most of these flaps have multidirectional scars that inevitably cross the RSTLs.

The vector of maximum tension runs perpendicular to a radial line bisecting the arc (Fig. 3). The flap should be oriented around a defect so as to place its tension vector away from distortable structures such as the lower eyelid and lip vermilion. If this is not possible, another flap should be considered. Finally, the orientation

Figure 3 The vector of maximum tension runs perpendicular to a radial line bisecting the arc.

of the scars should be with the RSTLs as much as possible. However, most of the flaps require incisions that will be unfavorable to the RSTLs. Some flaps do have a more linear orientation, including the subcutaneous pedicled and V-Y flaps, and these should be oriented with the RSTLs.

Single/bilateral-Pedicle Advancement (U-plasty/H-plasty)

Description

Single and bilateral pedicle advancement flaps are sliding random pattern flaps that involve advancing skin toward the defect from either one side (single pedicle or U plasty) or opposite sides (bilateral pedicle or H plasty) (Fig. 4). The shape of the flap is rectangular, taking advantage of the extensibility of the skin after wide undermining. These flaps are designed to include the subdermal plexus and the safe length to width ratio is 3:1; however, if the base is situated over a named artery this ratio can be increased. Burow's triangles usually must be excised lateral to the base of the flap to eliminate dog-ears.

Indications

The forehead is an ideal site for using this flap, making use of the horizontally oriented RSTLs. The arc is 90 degrees and the diameter 2D.

Advantages

The primary advantage of this flap is that it will fill smaller defects expeditiously, especially those on the forehead where the RSTLs are ideal for this type of tissue movement.

Disadvantages

There may be a tendency to overstretch the flap to accommodate larger defects, putting the crucial distal part of the flap in danger of ischemic necrosis; bilateral advancements help to overcome this limitation. Another disadvantage is the considerable additional incisions necessary to harvest the flap.

Island Subcutaneous V-Y Advancement

Description

The concept of the subcutaneous island advancement flap was first described by Esser in 1917 (10). This is a random-pattern sliding skin flap freed from its cutaneous

Triamgular Flap Skin
Figure 4 H plasty.
Advancement Flap

Incision

Figure 5 V-Y advancement flap.

Incision

Figure 5 V-Y advancement flap.

connections and advanced into a defect based only on the underlying subcutaneous tissue (Fig. 5). The degree of advancement possible is proportional to the amount and laxity of the underlying subcutaneous tissue. The donor defect is then closed primarily, resulting in a Y-shaped scar. The flap is triangular and should be as wide as the defect, but 1.5-2 times longer (11) (Fig. 6).

Indications

This flap is useful when the subcutaneous tissues in line with the defect are plentiful and lax. Cheek defects along the melolabial fold, especially adjacent to the ala are ideal. It may also be used to lengthen structures such as a shortened columella, or to release contracted scars that may be distorting surrounding structures such as the eyelid or vermilion. Additional indications include upper lip defects using bilateral V-Y plasties, or a single vertically oriented V-Y transposition for lower eyelid defects. The arc is 90 degrees and the diameter 1.5D.

Advantages

For flaps along the melolabial sulcus and lips, the topographical unit borders can camouflage the incisions. Very little tension results, due to the pushing effect on the island of skin from primary closure of the donor site. Skin color and texture match are excellent.

Disadvantages

Adequate subcutaneous tissue must be present to maintain flap vascularity. Therefore in areas with little subcutaneous tissue the flap is either unreliable or of very limited mobility (e.g., nasal tip). Since this flap is based on a vertically oriented blood supply, its application to scalp defects is limited due to the horizontally oriented blood supply in the galea aponeurosis.

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Responses

  • Isaias
    Is a nasolabial flap coded as an advancement flap?
    8 months ago
  • Elanor
    Is a local flap considered a fasciocutaneous flap?
    7 months ago

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