Flaps are defined as skin and subcutaneous tissue with an intact vascular supply moved to cover an adjacent primary defect.
History of the Procedure
Flaps typically are used in certain instances to take advantage of greater laxity in adjacent tissue, to change the direction of tension in the wound closure, or to camouflage a scar line. Simple linear closures are easier to perform, generally have lower complication rates than flaps and grafts, and typically leave an aesthetic linear or curvilinear scar. In addition, certain wounds (eg, those in concave areas such as the inner canthus or conchal bowl) do extremely well with second intention healing. Therefore, before the decision is made to close a surgical defect with a flap or graft, these other options must be considered. If a wound will not heal well by second intention and a linear closure will create too much tension, distort anatomic structures, or leave an unacceptable scar, flaps and grafts must be considered. Surgeons must not be too hesitant or too eager to use flaps. When used in the appropriate situation, a flap may offer the best aesthetic result.
Flaps can be categorized according to several different criteria:
- Local flaps come from within the same or an adjacent cosmetic unit.
- Distant flaps are transposed over intervening skin of one or more cosmetic units and, therefore, are from nonadjacent skin. These are completed in 2 stages; the pedicle is severed and returned to its initial position only when the local blood supply in the flap is developed.
- Free flaps are a combination of flaps and grafts. They share the characteristics of both because they are excised at a distant site with a major blood supply and harvested as a graft by severing them completely from the skin. Then, the artery is anastomosed to a major vessel in the surrounding skin. Thus, although skin is separated completely from its source (as in a graft), it carries its own blood supply, analogous to a flap.
- Axial pattern (arterial) flaps are flaps in which the blood supply to the flap is through a major vessel that is preserved when the flap is raised and the vessel is moved with it to cover the defect.
- Random pattern (cutaneous) flaps are flaps in which the subdermal vascular plexus is the source of the blood supply to the flap; these flaps are raised below the subcutaneous fat to preserve the plexus.
Primary tissue movementFlaps.See the list below:
- Advancement flap (see image above): These are flaps that involve advancement or linear slide of adjacent tissue to cover a primary tissue defect. Classic advancement flaps have the advantage of altering the position and location of a portion of the scar that may have been produced by a linear closure.
- Rotation flaps (see image above): These are flaps in which the tissue is rotated around a pivot point (arcuate slide) to cover a primary defect. Rotation flaps fill one defect by creating another defect that may be closed with less tension or distortion. Tension is redirected and redistributed.
- Transposition flaps (see image above): When the flap is carried (rotated) over an intervening area of normal skin to be placed in its recipient site, it is known as a transposition flap. Like rotation flaps, transposition flaps exploit skin laxity at a site distant to the surgical defect and redirect the tension of closure. Transposition flaps are generally smaller and freer in their movement than rotation flaps.
Transposition flaps take advantage of regional laxity by mobilizing tissue from an adjacent area of excess laxity (see image below) into the area without slack.
Transposition flaps have the following advantages:
They accomplish redistribution and redirection of tension.
They tend to be smaller in size than advancement and rotation flaps.
Resultant scars are geometric broken lines that may be less conspicuous and tend to be easy to hide.
Types of transposition flaps
Many different types of transposition flaps exist, with an innumerable amount of variations. The most commonly used transposition flaps include the following:
Classic rhombic flap, as described by Limberg in 1963
Modified rhombic flaps, such as the Webster 30° angle and the Dufourmentel flap
Banner-type flaps, such as the nasolabial transposition flap and the bilobed flap
Tunneled transposition flap (for deep defects of the nasal ala)
Transposition flap as a modification of island pedicle flap
Island pedicle flaps, by definition, are incised and completely separated from the surrounding skin except for the underlying pedicle that lies inferior to the flap. These closures are typically rotational or advancement in nature, which are effective for defects that are adjacent and require only sliding of the flap into place. However, for noncontiguous defects, island pedicle flaps are not an option. A modification of the island pedicle flap is a transposition movement. This enables repair of difficult and nonadjacent areas with sparing of normal tissue, allowing closure of the defect with noncontiguous but similar tissue and camouflage of scars into natural skin tension lines.
Although each patient must be evaluated individually, rhombic transposition flaps provide outstanding cosmetic and functional reconstruction options in certain classic areas of the face. These areas include the following (see image below):
See the list below:
Dorsum of the nose and the nasal sidewall: The use of surrounding skin in transposition flaps helps maintain optimal color and texture match. Keeping the mobile free margins of the eyelid and nasal ala in mind during the planning of flaps in this area is important. Any closure that distorts these in any way is unacceptable. Tension vectors should be directed away from these areas. The nasal tip is also mobile and should be considered in the closure of nasal defects. However, the tip ptosis that frequently occurs with increasing age may be corrected aesthetically with some closures (see images below).Post-Mohs surgical defect over the right nasal sidewall in a 38-year-old woman.Reconstruction of the right nasal sidewall defect with a superiorly based Dufourmentel flap.Side view of the nose, 3 months postreconstruction of the right nasal sidewall defect.Front view of the nose with no distortion of the structure and maintenance of the nasal symmetry.
Inner and outer canthus: Because of the proximity to neighboring mobile anatomic structures, such as the eyelids, redirection of the tension vectors by optimal orientation of the transposition flaps prevents distortion of these structures after closure of the defect. The acute angles of the folds (crow's feet) in the outer canthus offer excellent lines to hide the acute angles generated by transposition flaps.
Temple: Transposition flaps use the reservoir of excess skin over the cheeks, temple, and preauricular areas to repair large defects over the temple where primary closure may not be possible.
Cheeks: Because the skin of the cheek is richly vascular due to the favorable blood supply from the subdermal plexus, the viability of transposition flaps is less critical, which may be used to create scars as geometric broken lines that tend to be well camouflaged within the skin creases. Transposition flaps typically are designed laterally and with the redundant tissue inferior to the primary defect. This keeps the scar in a lateral position, and the inferiorly based flap maintains optimal lymphatic drainage to help prevent pin-cushioning (see images below).Postoperative Mohs defect on the right cheek of a 69-year-old man.Reconstruction of the right cheek defect with a superiorly and laterally based Dufourmentel flap.One-week postrepair of the right cheek defect with the resultant scar placed laterally to make it less noticeable.Three months postreconstruction of the right cheek defect with the Dufourmentel flap.
Perioral: Using the laxity of the adjacent cheek and hiding scars in the various folds and normal wrinkles in this area make transposition flaps a good option (see images below).Postoperative Mohs defect over the left inferior angle of the mouth in a 60-year-old man.Reconstruction of the surgical defect with a superiorly based Dufourmentel flap to prevent distortion of the lower lip.Three months postrepair of the left inferior angle of the mouth defect with the Dufourmentel flap (close-up view).
Chin: Transposition flaps may use neighboring areas of regional laxity and reservoirs of skin, such as the skin of the submandibular area and neck, to good advantage in the closure of selected defects (see images below).Postoperative Mohs surgical defect over the left chin in a 74-year-old woman.Reconstruction of the surgical defect with an inferiorly and medially based Dufourmentel flap.Three months postrepair of the left chin surgical defect with the resultant scar hidden well in the submental crease.Three months postrepair (front view) of the left chin defect with no distortion of the neighboring anatomic structures and maintenance of symmetry.
A computational model of cutaneous wound closures developed by Topp et al indicated that, in rhombic transposition flaps, the extent of secondary tissue movement is determined by the width of the flap, as is the flap’s effect on surrounding tissues, while the transposition angle is responsible for the orientation at which maximal strain occurs. 
Banner-type transposition flaps 
The classic banner-type transposition flap is a finger-shaped random pattern (cutaneous) flap that makes use of areas of adjacent laxity. This flap allows for the placement of a long linear secondary scar in a skin fold or crease or along the junction of 2 cosmetic units. This type of flap most commonly is used in the following areas:
Ala: The classic nasolabial transposition flap is used.
- The banner flap is taken behind the superior aspect of the ear. Reconstruction of the upper one third of the ear may be achieved using several strategies such as full-thickness skin grafts, wedge resection with subsequent primary closure, helical advancement flaps, multistage preauricular or postauricular tubed flaps, and one-stage preauricular or postauricular transposition flaps. [6, 7]
- When defects are smaller than 1.5 cm, wedge conversion of the defect followed by primary closure is aptly suited without distortion of the anatomy. However, when the defect is 1.5-2.5 cm, the best choice is helical advancement flap. For helical defects greater than 2.5 cm, a multistaged tubed flap (anterior or posterior) is considered.
- To reconstruct a similarly sized defect, a postauricular transposition flap can be performed as a single-stage procedure. The anterior edge of the flap is cut along the retroauricular sulcus. The flap is designed to have a length-to-width ratio of 1:4 (exceeding the length of the defect). A burrow triangle is added to the flap to allow easy closure of the secondary defect by tapering the tip of the secondary defect. Because the postauricular skin is thin, undermining should be done with care. After trimming the flap to fit the defect, the first suture is placed at the tip of the flap and secured to the remaining helix with a vertical mattress suture to allow good eversion and avoid notching of the rim. The rest of the flap is then sewn into place with routine simple interrupted sutures.
- A cartilage graft may be harvested from the opposite ear to re-form the rim if there is significant cartilage loss in the primary defect. The possibility of a trapdoor deformity may be desired here to some extent because it would help to recreate the natural helical rim contour. Therefore, an anteriorly or posteriorly placed transposition flap can be effectively used for reconstruction of superior helical rim defects located proximally, enabling a single-stage procedure in place of a multistage interpolation flap.
Medial anterior ear (ie, concha, tragus, crus of the helix): The banner flap is taken in the preauricular area (see images below).Postoperative Mohs defect in the right concha of a 58-year-old man.Reconstruction of the right conchal surgical defect with a Banner transposition flap.Three months postrepair of the right conchal surgical defect with no distortion of the structure of the ear.Three months postrepair of the right conchal surgical defect (close-up view).
The bilobed flap is a double-lobed modification of the banner transposition flap described above. The principle of transposing skin from an area of laxity remains the same; however, the transfer of tissue is in 2 steps and allows the donor skin to be at a greater distance from the recipient area.
The basic motion of the flap is that of rotation. Each lobe of the flap is tethered to a cutaneous pedicle, which creates the same pivotal restraint on the movement of the flap as a rotation flap.
There are 2 important variables in the construction of a bilobed flap, namely, the flap length and the flap angle, which relate to each other directly. Greater angles of rotation require longer flaps to overcome the pivotal restraint. Typically, the first lobe of the flap is designed to be equal to the width of the original defect. If the location of the primary defect is in an area that allows secondary motion, the first lobe may be designed up to 20% smaller than the primary defect. The primary lobe can be thinned if bulky; however, deepening the defect may be preferable to thinning the lobe, thus increasing the risk of flap necrosis.
The second lobe also may be designed smaller because tension can be shared by closure of the defect created by the second lobe. In addition, the second lobe of the flap is constructed with an elliptical tip to facilitate side-to-side closure of the tertiary defect. The movement of the flap is facilitated through wide undermining around the flap, especially at the pedicle. The undermining is deep and wide just above the level of the perichondrium or periosteum. In this way, the muscle remains attached to the base of the pedicle ensuring a rich vascular supply (see image below).
A modification of the original bilobed flap was described by Zitelli in 1988 (see image below) and is the most used design of the bilobed flap. 
In this, a triangle or a dog-ear cone is designed along one side of the circular defect, orienting the line of closure along the resting skin tension lines or a cosmetic unit junction line without the distortion of neighboring free margins. This has the advantage of maintaining a rich vascular supply to the flap because this does not cut into the base of the defect. Also, it prevents a secondary procedure to remove the standing cutaneous deformity (dog-ear) that occurs at the point of rotation.
An arc is then extended from the defect tip up to 90°, and the 2 lobes of the flap are drawn along this arc (see image below).
The 2 lobes should be separated by an angle of 30-45° to limit the size of the dog-ear and to reduce the risk of pin-cushioning (see images below).
Because some degree of pivotal restraint is created by the motion of rotation and the lobes may be shortened slightly in the rotation, the first lobe of this flap may be designed to extend beyond the arc (see image below).
Thus, as the flap is rotated and transposed into position, the lengthened lobe fits into the primary defect without any tension (see images below). The lobes should be inset or flush with the adjacent skin. A tacking suture may be placed in the defect to the underside of the primary lobe to avoid trapdooring.
The bilobed flap is particularly suited for reconstruction of the defects located over the following areas (see image below):
See the list below:
Nasal tip and supra-tip (see images below)Postoperative Mohs defect over the left tip of the nose in a 71-year-old man.Reconstruction of the left nasal tip surgical defect with a bilobed flap to provide a good texture and color match.Three months postrepair of the left nasal tip.Three months post repair (front view) with no distortion of the tip.Three months postrepair with a well-blended scar line (side view).
Nasal sidewall (see images below)Postoperative Mohs defect over the left nasal sidewall in a 45-year-old woman with a bilobed transposition flap marked for repair.Three months postreconstruction of the surgical defect over the left nasal sidewall with a bilobed transposition flap
Medial nasal ala
Auricular helix (see images below)Postoperative Mohs defect over the helix of the right ear in a 59-year-old man.Reconstruction of the right helical surgical defect with a bilobed flap exploiting the laxity of the postauricular skin.Three months postrepair of the right helical surgical defect with the bilobed flap.Three months postrepair of the right helical surgical defect showing intact helical rim with no distortion of the structure of the ear.
Transposition island pedicle flap
This is best used over the following areas:
Nasal side wall
Extranasal applications of the bilobed flap
The novelty of the bilobed flap as it is used for extranasal reconstruction is that the surgeon has some degree of variance in designing the size of the individual lobules of the flap, with a lower risk of secondary tissue distortion. The flap must be carefully designed to place the incision lines as closed to the relaxed skin tension lines as possible, and a meticulous suture technique is important for camouflaging the complex suture line of this flap. Importantly, keep in mind that the extranasal bilobed flap's vascular support may be reduced compared with nasal sites. The extranasal sites where the bilobed flap may be used are as follows:
Chin: Particular attention must be given to avoiding damage to the marginal mandibular nerve during execution of this reconstructive technique.
Medial cheek: To eliminate the transfer of hair into a reconstructed surgical wound, the surgeon may thin the flap and destroy the hair bulbs at the time of flap insertion; to avoid flap necrosis, avoid excessively thinning the distal portion of the flap.
Dorsum of the hand: The secondary lobule of the flap in this case may be somewhat undersized compared with the design of the flap used in nasal reconstruction.
Tunneled transposition flap
The tunneled transposition flap is a single-staged flap for the repair of deep defects of the nasal ala that do not lend themselves to skin graft repairs. When a decision is made by the surgeon to use this particular flap, 2 important considerations must be addressed. First, the defect should be limited to the nasal ala entirely in order to achieve a good aesthetic outcome, because recreating the alar crease is impossible with this flap. Second, the alar defect must be deep because this flap requires a pedicle, and, if the depth of the defect is not enough to fit the pedicle, the result would be a pin-cushion deformity. Additionally, if an attempt is made to thin the pedicle in order to fit the defect, the blood supply to the flap may be compromised. Therefore, if the alar defect is shallow, a full-thickness skin graft is the ideal choice or else the defect has to be deepened.
The flap is planned such that it lies along the melolabial fold so that the secondary defect is closed along a natural cosmetic line. The major advantage of this flap over a banner-type flap is that with the tunneling, the alar crease is entirely preserved.
Smoking, aspirin, and anticoagulant use are relative contraindications to the use of transposition flaps because they interfere with the healing of the flaps and, therefore, increase the incidence of flap necrosis. Herbal supplements containing such substances as gingko biloba also have some anticoagulant activity. The use of these substances should be addressed at the time of preoperative evaluation so that they may be discontinued a few weeks prior to surgery if it needs to be performed.