Concepts in local flap design and classification

To ensure flap viability, a solid understanding of cutaneous anatomy is important (Figure 1). The epidermis represents the most superficial layer of skin. Beneath the epidermis lies the dermis, which is composed of the superficial papillary and deeper reticular layers. Within the dermis there are two distinct vascular arcades: a superficial vascular plexus that runs between the reticular and papillary dermis, and a more robust deep vascular plexus or “subdermal” plexus that runs between the reticular dermis and subcutaneous tissue. The skin also receives blood supply from direct cutaneous arteries that arise as perforators off deeper musculocutaneous arteries. Local flaps can be classified based on their blood supply (Table 2). Random flaps depend on the vascular supply of the subdermal plexus and not a named skin perforator. The length of the random flap depends on the intravascular resistance of the supplying vessels and the perfusion pressure. When the perfusion pressure drops below a critical closing pressure of the arterioles in the subdermal plexus, nutritional blood flow ceases and flap ischemia occurs. Therefore, the traditional concept of a width-to-length ratio does not dictate flap survival, rather perfusion pressure does. Axial flaps are flaps based off a specific direct cutaneous artery (also called septocutaneous artery) or musculocutaneous artery. These flaps have a more generous blood flow with improved survival lengths. Both regional flaps, such as the pectoralis major flap, and free flaps, such as the radial forearm flap, are considered axial flaps. Thus, free flaps represent the most extreme concept of axial flaps given the initial total blood supply is dependent on the revascularization of a single anastomosed artery.

Local flaps are also categorized based on composition (Table 3). The composition of the defect to be reconstructed should dictate the correct composition of the flap used for reconstruction. The classification is self-descriptive. These include cutaneous, fasciocutaneous, musculocutaneous, and osteomusculocutaneous (Figure 2). Any variation of these flaps can exist with removal of the outermost layers. For example, many free flaps can lack skin or bone and be solely a musculofascial flap.

Flaps are most commonly described based on the method of transfer (action on the nutrient pedicle) and design (Table 4). Advancement flaps depend on the advancement of the surrounding tissue along a linear axis to close a defect (Figure 3A-F). The advancement of two skin edges from a fusiform skin excision represents the simplest of advancement flap design. Classically, advancement flaps have a length-to-width ratio of 1:1 or 2:1.^,  Advancement flaps often create standing cutaneous deformities or “dog-ear” deformities, which must also be addressed as part of the reconstruction plan.

Rotational flaps are pivoted around a fixed point at the base of the flap and rotated along an arc toward the defect (Figure 3G, H)). Classically, rotation flaps are designed to move along an arc of 30 degrees or less with the radius approximately two to three times the diameter of the defect and the arc length approximately four to five times the width of the defect. Most rotational flaps possess a component of advancement and thus are more accurately labeled rotation-advancement flaps (Figure 4).

Transposition flaps are versatile flaps whose design creates a second defect. The flap is raised from a donor site and rotated over an incomplete bridge of skin to be placed into the defect site. The donor site must also be closed as part of the design. The three classic transposition flaps include the rhombic flap, bilobed flap, and Z-plasty^{,  ,}  (Figure 5, Figure 6, Figure 7). As with most reconstructions, rarely do flaps fit the classic design; therefore, many modifications of classic designs have been created. For example, the Dufourmental and the Webster modifications of the rhombic flap are designed to create smaller angels of rotation that result in less redundancy and smaller standing cone deformities. Similarly, the original bilobed flap design was based on an arc of rotation of 180 degrees. Zitelli then redescribed the bilobed flap based on an arc of rotation along a 90-degree axis, which created less tension on the closure and less chance for a standing cone deformity.^,  Additionally, the complex design of transposition flaps often make it difficult to create scars that completely rest within relaxed skin tension lines.

Interpolated flaps are pedicled flaps that cross over or under intervening intact tissue (Figure 8). If the flap passes over intact skin, the flap must be divided and inset in a second stage of reconstruction. In contrast to transposition flaps, the base of interpolated flaps is not contiguous with the defect base. Interpolated flaps are often dependent on an axial blood supply. The most classic facial interpolated flap is the paramedian forehead flap, which receives blood supply from the supratrochlear artery. Additional examples are described in Table 4.

Free flaps represent the transfer of tissue based on an axial blood supply from a distant body site. These flaps require microvascular anatomosis of the arterial and venous systems for survival. In the correct patient, free flaps offer excellent survival rates with abundant tissue to fill any defect size and composition.

Classification of flaps provides a clear understanding of the flap properties. However, with so many reconstructive options, choosing the correct reconstructive plan relies on a systematic approach to analyzing the patient and facial defect. Below are key points that aide in organizing and optimizing reconstructive planning (Table 5).

• 1
  Analyze the facial defect and characterize the defect based on skin color, skin thickness, tissue composition, location, and subunits involved

  ¹²

  • Burget G.C.

  Modification of the subunit principle.

  Arch Facial Plast Surg. 1999; 1: 16-18

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  ^, 

  ¹³

  • Burget G.C.
  • Menick F.J.

  The subunit principle in nasal reconstruction.

  Plast Reconstr Surg. 1985; 76: 239-247

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  (Figure 9). If the defect involves greater than 50% of the subunit, resection of the entire subunit may allow for improved aesthetic outcomes by camouflaging the incisions at the borders of the esthetic subunits. Composition is especially important when dealing with full thickness defects of the eyelid, nose, and lip. Define the composition with respect to existence of an internal layer (such as conjunctiva or mucosal lining), structural layer (which may be represented by muscle, cartilage and/or bone), and external skin layer. Failure to reconstruct all layers ultimately results in collapse or retraction of the original reconstruction. Therefore, all layers absent must be reconstructed to receive optimal functional and aesthetic outcomes.

• 2
  Once the defect has been well characterized, options for reconstruction can be considered using a graduated approach (Table 6). The reconstructive ladder represents techniques used to close defects that become progressively more complex. The ladder from simplest to most complex is healing by secondary intention, primary closure, skin grafting, tissue expansion, local tissue transfer, distant tissue transfer, and free flap. The character of the defect, including composition and thickness, should be considered to determine the most appropriate match for reconstruction. It is important to create more than one plan for closure to allow for unpredictable findings during surgery.
  Table 6Reconstructive ladder

  - Healing by secondary intention - Primary closure - Delayed primary closure - Skin grafts - Split-thickness skin graft - Full-thickness skin graft - Tissue expansion - Local tissue transfer - Random - Axial - Distant pedicled tissue transfer - Free flap

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• 3
  When designing the surgical options for reconstruction, it is crucial to consider the surrounding anatomy. Determine acceptable areas of tissue recruitment and respect facial landmarks that do not tolerate distortion (Table 7). Landmarks that should not be distorted include hairline, eyebrow, eyelid and canthi, nasal tip, nasal ala and alar rim, earlobe, philtrum, vermilion, and oral commissures. Areas that provide a good source of tissue for recruitment include the forehead, cheek, chin, submenton, and neck.

  ¹¹

  • Calhoun K.H.
  • Seikaly H.
  • Quinn F.B.

  Teaching paradigm for decision making in facial skin defect reconstructions.

  Arch Otolaryngol Head Neck Surg. 1998; 124: 60-66

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  Table 7Facial landmarks

  Nondistortable landmarks	Tissue good for recruitment
  - Hairline	- Forehead (tight skin)
  - Eyebrow	- Cheek (lax skin)
  - Eyelid and canthi	- Chin
  - Nasal tip	- Submenton
  - Nasal ala	- Neck (lax skin)
  - Earlobe
  - Philtrum
  - Vermilion
  - Oral commissure

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• 4
  Once the ideal areas for tissue recruitment have been chosen, flaps should be designed such that the scars rest within the relaxed skin tension lines and close parallel to the lines of maximal extensibility

  ¹⁴

  • Larrabee Jr, W.F.

  Design of local skin flaps.

  Otolaryngol Clin North Am. 1990; 23: 899-923

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  (Figure 10). Incisions designed along subunit borders will fall within the relaxed skin tension lines. Ideal borders to camouflage scars include the melolabial creases, supratarsal creases, mental crease, philtral crests, vermilion borders, and anterior hairline.

• 5
  It is important to consider the patient's medical condition while formulating the reconstructive plan. History of radiation, immunocompromise, diabetes, and smoking increase complication risks of the reconstruction. Therefore, in the setting of compromised tissue, opt for improved survival over improved esthetic outcomes. This often translates into using reconstructive options lower in complexity on the reconstructive ladder. Following these key steps will allow for an organized approach in designing reconstructive plans for facial defects.

In summary, facial reconstruction relies on the creativity of surgeons as well as a clear understanding in the properties of local flaps. Choosing the correct procedure begins with thorough analysis of the defect. Multiple reconstructive options often exist, which can then be narrowed and refined based on the specific qualities of the defect and the history of the patient. Careful planning ultimately leads to an excellent functional and esthetic reconstructive outcome.