Flaps can be used when closing wounds by second intention, primary linear closure, or when skin grafting would result in functionally or aesthetically unsatisfactory results. For these reasons, they are an invaluable tool to the dermatologic surgeon. They are categorized by blood supply into axial flaps, which are supplied by a named artery, and random pattern flaps, which rely on the vascular plexus of the dermis and subcutaneous tissue. The type of primary movement or motion of the flap can further subdivide random pattern flaps into three categories: advancement, rotation, and transposition. Advancement and rotation flaps, also called sliding flaps, recruit adjacent lax tissue and move in either a linear or arced (respectively) motion to fill in the primary defect. Transposition flaps, also called lifting flaps, recruit noncontiguous donor tissue that is incised and lifted over intact skin and placed into the primary defect. Transposition flaps most commonly used in dermatologic surgery include the bilobed, rhombic, and nasolabial (melolabial) transposition flaps as well as the Z-plasty.
Transposition flaps are used when surgical defects pose a risk of functional impairment and/or aesthetically displeasing results if repaired by a simple primary closure, second intention, skin grafting, or sliding flaps. Advantages of transposition flaps include less undermining when compared to large, sliding flaps and superior ability to displace tension away from the defect and any nearby free margins, as well as to re-orient tension vectors in more favorable directions. Rhombic transposition flaps are particularly useful for defects near the medial and lateral canthi, cheeks, and lateral upper two-thirds of the nose, but they also have a well-defined role in the lateral forehead, temple, perioral, inferior chin, and dorsal hand defects. Bilobed transposition flaps can be utilized in defects of the lower third of the nose, the helix, and posterior ear. Nasolabial transposition flaps are used for medium-sized defects of the nasal ala. The Z-plasty can improve cosmesis of scars crossing relaxed skin tension lines and be helpful to release scar contractures by redistributing tension over the wound.
The contraindications of transposition flaps should be considered before their use in repairing a particular defect. Patient selection remains essential. Functional status with close attention to comorbidities and ability to care for the flap needs to be assessed before the repair. These procedures should be avoided in patients who are poorly compliant or cannot leave their surgical sites undisturbed. Additionally, patients who are unable to carry out post-surgical instructions due to disability or comorbidities (such as dementia) without access to other medical care should be considered a relative contraindication.
Absolute contraindications to the usage of a flap include failure of tumor clearance and active infection involving the flap. Failure to fully clear the tumor, particularly the deep margin, can lead to recurrent tumors growing unrecognized for long periods of time along planes of undermining and larger tumor burden when detected. This risk can be minimized by margin control via adequately excised margins or Mohs micrographic surgery. The infected skin should never be used to make a flap or covered by one as this increases morbidity and complication rates including flap failure.
Relative contraindications include smoking, bleeding diatheses, or predisposition to impaired vascular supply. Smoking increases the risk of flap necrosis, wound dehiscence, prolonged healing times, and infections. Recommending smoking cessation from two weeks prior to one week after surgery may help to minimize these complications. Patients with an inherited bleeding diathesis or on antiplatelet or anticoagulation therapy are at increased risk of perioperative or postoperative bleeding and hematoma. Consultation with specialty physicians prior to operating on patients with a known inherited bleeding diathesis is advised. Antiplatelet and anticoagulant medications, when appropriately managed, are generally continued during surgery to avoid the risk of adverse thrombotic events. Use of tissue with impaired vascular supply, such as previously irradiated skin or scar, is generally avoided as it can decrease blood flow of the pedicle and the potential viability of the flap.
Equipment needed to perform a transposition flap is similar to that needed for other dermatologic surgery.
At least one surgical assistant is helpful to help manage intraoperative bleeding, cut suture, and to place a postoperative dressing.
Depending on the patient, it can be helpful to show or describe the size of the defect after tumor clearance and explain the chosen transposition flap as well as the expected scar. Addressing the patient’s expectation is key to proper care of the flap as well as the perceived outcome. Patients often underestimate the size of the tumor, and satisfaction may be improved by allowing them to understand or see the size of the defect after tumor clearance and subsequent expected scar. Photographs should be taken prior to incision, the defect after tumor clearance, and the repair. Discussing typical postoperative changes and the potential need for revisions, such as laser or dermabrasion, should be addressed as well.
All transposition flaps should be planned and drawn meticulously before execution as even the smallest error in planning can have dramatic functional and aesthetic consequences. Again, tumor clearance before flap implementation is of utmost importance. Previous scars, facial subunits, relaxed skin tension lines and lines formed from facial expression should be noted at rest and with movement.
The rhombic flap was originally described by Limberg in 1963 and is often called the Limberg flap. It is particularly useful for defects of the medial and lateral canthi, cheeks, and lateral upper two-thirds of the nose but also has great utility in defects of the lateral forehead, temples, perioral region, inferior chin, and dorsal hands. In the classic Limberg design, the defect is surgically excised (preferably with a slight outward bevel) as a rhombus with two opposing 60-degree angles and two opposing 120-degree angles. The flap is designed off the short axis of the defect. Advantages of this design include a smaller secondary defect as well as four possible arrangements of the flap, allowing surgeons to select the orientation that produces the ideal wound closure with low scar tension. The flap arrangement chosen should be designed so that the donor-site closure (secondary defect) is aligned to take advantage of the area of maximum laxity.
After the rhombic defect is created and flap planned, incision of the flap is performed with one incision that extends off the selected short axis at a 120-degree angle and equal in length to the sides of the rhombus. A second incision of equal length extends from the endpoint of the first incision to form a 60-degree angle. The flap should be undermined at a depth equal to that of the defect and lifted into the primary defect. After wide undermining of the primary and secondary peripheral defect edges, hemostasis should be attained and the secondary defect approximated in layers using deep dermal (4-0 or 5-0) sutures and superficially with simple interrupted or vertical mattress sutures (5-0 or 6-0). The flap should then be sutured into the primary defect similarly. The finished rhombic transposition flap should look similar in shape to a question mark.
Variations of the classic Limberg rhombic flap also are common in dermatologic surgery. The DeFourmental flap narrows the angle of the tip of the secondary defect and creates a shorter arc of rotation for the flap by incising the first line at the angle made by bisection of the first line of the Limberg and extension of one side of the rhombus (the second incision is still made at a 60-degree angle to this first incision). The Webster flap is made similarly to the DeFourmental Flap, but rather the second incision is made at a 30-degree (rather than 60-degree) angle to the first incision. Both of these modifications allow for tension sharing between the primary and secondary defects.
Esser originally described the bilobed flap in 1918, which was later modified in 1989 by Zitelli. It is particularly useful in repairing defects of the lower third of the nose, but it can also be used on other parts of the face, neck, helix and posterior ear, eyelids, feet, hands and trunk. The bilobed flap consists of two lobes based on a single pedicle and has the advantage of recruitment of more mobile tissue with more favorable tension vectors. Zitelli’s modified bilobed uses 45-degree angles (rather than 90-degrees in Esser’s design), minimizing dog-ears (tissue protrusion) and pincushioning.
The bilobed flap is constructed based on a circular or oval defect. A pivot point is selected at least one radius away from the edge of the defect and lines are drawn tangential to the edges of the circle to delineate the Burow's triangle that will be excised (to prevent dog-ear formation). The first or primary lobe is drawn at a 45-degree angle from the pivot point with identical length and diameter of the defect (some will use a slightly smaller base or slightly longer flap). The secondary lobe is centered at a 90-degree angle from the pivot point (45 degrees from the center of the first lobe), should be slightly longer than the first lobe yet narrower towards the base (approximate width of half to a full diameter of the primary lobe), and be excised with a triangular tip to create a linear scar at the tertiary defect. The width of the secondary lobe is a balance between being small enough to allow easy closure of the tertiary defect but large enough to close the primary defect site with surrounding structural displacement. Wide undermining of the flap and the peripheries of the donor and defect site should be performed after flap incision and excision of the defect’s Burow's triangle. Hemostasis should be attained, and the flap lifted and rotated approximately 45-degrees so that the primary lobe fills the original defect and the secondary lobe fills the primary lobe donor site. The tertiary defect is closed first using deep dermal (4-0 or 5-0) sutures, followed by deep dermal suturing of the primary lobe into the defect. The secondary flap tip is then trimmed to precisely fit the remaining defect (primary lobe donor site) and sutured similarly. Superficial simple interrupted, vertical mattress or occasionally running/simple continuous (5-0 or 6-0) sutures are placed to re-approximate the superficial epidermal edges. The finished bilobed flap has a closure that resembles the shape of the top of a heart.
Variations of the classic Zitelli bilobed flap include the trilobed transposition flap. This flap is particularly useful with larger alar defects and/or rigid sebaceous nasal skin and aims to prevent the ipsilateral alar depression and contralateral alar elevation that can be seen after repaired. It is designed similarly to the bilobed flap with approximately 45-degree angles between lobes but has three lobes rather than two. This can keep the tension vector perpendicular to the nasal ala and maintain alar symmetry.
Nasolabial (Melolabial) Transposition Flap
Dieffenbach originally described the nasolabial flap in 1830 when he used superiorly based nasolabial flaps to reconstruct the nasal ala. This was modified by Esser around 1920 when he used an inferiorly based flap to close a palatal fistula and formed the basis of what is used more commonly today. It is particularly useful for defects of the lateral and central ala. The nasolabial flap is harvested from the relatively sebaceous skin in the medial cheek adjacent to the nasolabial fold before being transposed in the alar defect, allowing the scar to hide well in the nasolabial fold. Although historically a two-step surgical reconstruction, if planned and designed appropriately, it can be done as a single-staged repair.
The nasolabial flap typically is planned around a circular defect on the lateral or central ala. Planning is started by designing the superior dog-ear above the primary defect, which should be relatively tall and narrow with no more than a 30-degree apical angle. The medial margin of the flap is drawn within the nasolabial fold and the lateral margin on the medial cheek, extending superiorly only as high as the point over which the flap is to be transposed. It should be noted that the flap is planned longer than that of the primary defect (after dog-ear excised) to compensate for shortening that will occur as the flap is lifted onto the nose. The base of the flap should be similar in width to the defect. After excision of the dog-ear and incision of the flap, the wide undermining of the cheek at the donor site is needed to medially advance the cheek. Hemostasis should be attained. Most will place a tacking or anchoring suture from the dermal undersurface of the flap (in the dermis) to the periosteum of the nasal bone or maxilla in the concavity of the nasofacial sulcus to minimize tension of the flap on the alar defect when sutured into place and to minimize blunting of the nasofacial sulcus. The secondary defect is closed using deep dermal absorbable (4-0 or 5-0) sutures, and the flap lifted into the alar defect. The flap should be carefully trimmed to fit the defect, and miscalculations can result in functional or aesthetic problems such as alar retraction and pincushioning. Epidermal edges are then approximated using simple, interrupted or running/simple continuous nonabsorbable (5-0 or 6-0) suture.
The first example of the contemporary Z-plasty was by Berger in 1904. Modifications for improvement were made by Morestin in 1914 and understanding of the flap’s dynamics by Limberg shortly after. This transposition flap is used primarily in the revision of scars after dermatologic surgery. Potential indications include improvement of scar cosmesis by changing the direction of the scar, particularly those crossing relaxed skin tension lines and releasing scar contractures by redistributing tension over the wound, which is important in those near free margins with visible deformity. This technique creates two flaps from three equal limbs and two same-degree angles and ultimately results in a lengthening of the scar.
The first limb of the Z-plasty is drawn along the axis of the scar from one edge to the other. Two equal-sized limbs are drawn at identical angles on either end of the first limb. The symmetry of all the limbs and the angles of their junction is key to the success of this flap. The angles formed by the junction of the limbs should be between 30 and 75 degrees; less than 30 degrees may incur tip necrosis, whereas greater than 75 degrees creates flaps that are difficult to rotate, increased tension, and potential for dog-ears. The angles also dictate the expected lengthening of the scar size: 30, 45, and 60 degrees result in a 25%, 50%, and 75% gain in tissue length, respectively. After careful planning, an incision along or around the scar and the outlined limbs is made. Wide undermining should take place on both triangular flaps that are formed as well as the edges of the wound, followed by meticulous hemostasis. The tips of the flaps are then transposed. Deep dermal absorbable (4-0 or 5-0) sutures are placed starting with the lateral limbs, and the epidermal edges are approximated using simple, interrupted or vertical mattress nonabsorbable (5-0 or 6-0) suture.
The possible complications of these procedures include swelling/edema, pain, infection, flap necrosis, scarring, bleeding/hematoma, and hypertrophic scar/keloid. Fairly specific to transposition flaps is the trapdoor effect in which there is a "pincushion" appearance (elevation of part of the flap above surrounding skin). This phenomenon can be aggravated by insufficient tissue undermining, an oversized flap, excess subcutaneous fat in the flap, or insufficient flap contact with the wound base.
Transposition flaps are a common modality in dermatologic surgery for repairing surgical defects that may otherwise be functionally or aesthetically compromised when other reconstructive methods are used.