Transposition Flaps Treatment & Management

Surgical approaches are described for the classic rhombic flap and for rhombic flap modifications.

Classic rhombic flap

The classic rhombic flap is constructed around a defect that is converted into a geometric 4-sided defect (rhombus) with equal side length and tip angles equal to 60° and 120°. It classically is designed by extending the short diameter of the defect (X) beyond the flap for a length equivalent to one of the sides (see image below).

Then, the flap is created by drawing a line from the free end of the extended short diameter parallel to one of the sides of the existing rhombus (see image below).

When designed in this manner, the tip angle is 60°. The flap typically is designed off the short axis of the defect to keep the flap as small as possible (see image below).

A flap can be constructed in 4 possible directions for any rhomboid defect off its short axis (see image below). The optimal flap is chosen out of the 4 possibilities, keeping in mind the considerations outlined below.

Best tension distribution

The flap uses the area of maximum tissue laxity with no effect on the surrounding anatomic structures when the flap is closed with no distortion of free margins (see image below).

Best scar line

Orient the flap such that most of the resultant scar line lies along relaxed skin tension lines (see image below) or at the junction of 2 cosmetic units. In addition, if all else is equal, the scar should be placed in a lateral position.

When patients look in a mirror and when they have face-to-face communication, a laterally placed scar is hidden much better than a medially placed scar (see images below).

Flap dynamics

The flap is designed (see section A of image below) and cut along the incision lines. It is undermined widely and rotated into the defect (see section B of image below). The secondary defect is closed with the first tension-bearing suture. However, even after the donor defect is closed, the flap is not completely tension free.

Some shortening in the length of the flap occurs because of the restraint at the pivot point of the pedicle. Therefore, the leading flap tip does not quite meet the recipient tip. For the tips to meet, there must be some movement of the recipient tissue toward the flap and/or some degree of flap advancement (see section C of the image above). If this does not occur, the forceful pulling of the tip carries the risk of tip ischemia and necrosis. If no movement is possible in this direction, the flap may be oversized to compensate.

The classic rhombic flap has 2 major tension sites. The first and primary tension site is at the closure of the secondary defect, and the second site is at the closure of the leading tip. To ensure success of the flap, the surgeon must understand and plan for these tension forces. The tension may be minimized by the following modifications:

• Lengthening the leading edge of the rhombic flap and elongating the secondary limb of the flap enlarges the flap while ensuring that the flap tip meets the recipient tissue without tension (see image below).

  Classic rhombic flap.

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• The leading tip may be made to reach the recipient tip in a tension-free environment if the flap angle is made slightly more obtuse, ie, greater than 120° (see image below).

  Classic rhombic flap.

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Rhombic flap modifications

Webster flap ^[21]

In this modification of the rhombic flap, the tension is not fully displaced but rather shared by the lax adjacent tissue. It is designed by decreasing the flap tip angle to 30°, and the base of the flap is only half the length of the recipient defect (see image below).

This narrows the flap pedicle and increases the side-to-side tension on the flap as the defect is closed. By doing so, the tension is shared between the area of the defect and the adjacent tissue where the flap is harvested. This additional tension, if too great, may increase the risk of flap ischemia or necrosis.

This flap most commonly is used when 2 flaps must draw from different tension vectors such that each flap closes one half of the defect, reducing the angle from 60° to 30°.

Dufourmentel flap ^{[22, 23, 24]}

This is a modification of the rhomboid transposition flap. The flap is designed by extending one line from the short axis to a length equivalent to the side lengths, similar to a classic rhombic flap, and another line is drawn by extending the side adjacent to the lower angle to a similar length (see image below).

However, the incision is made along a line that bisects these 2 extended lines (see image below).

A second incision is made along a line that is dropped from the end of the bisected line parallel to the long axis of the rhombic defect to complete the flap (see image below).

By using a line drawn parallel to the long axis instead of one of the sides of the rhombic defect, the pedicle is widened but the movement is inhibited. Therefore, for the flap to rotate to its receptor angle completely, some degree of upward advancement is essential.

A key feature of the flap is the obtuseness of the leading angle. This relieves the pivotal restraint to some extent and results in more lateral tip tension compared to more vertical tip tension in a classic rhombic flap. Therefore, the Dufourmentel flap is useful in areas where lateral tension is acceptable and vertical pull is not.

Although this article deals with the construction of transposition flaps for rhomboid-shaped defects, the same principles may be used to reconstruct a circular defect. For this, the defect remains circular, and a rhombic design is drawn around it. With a circular defect, the flap may be designed in any direction, keeping in mind the optimal flexibility of the surrounding tissue and adjacent anatomic structures. The optimal closure lines are determined according to the resting skin tension lines or cosmetic unit junction lines and are transposed to the circular defect axis (the diameter of the circular wound). See image below.

The length of the line extended beyond the defect is longer than the circular diameter because this diameter is shorter than the short axis of the rhomboid drawn around the circular defect. A second line of the same length is drawn, keeping a tip angle of 60° to complete the flap (see image above). The tissue redundancy created by the rotation of the transposition flap is removed with trimming of a triangle at the pivot point. The transposed tissue may be rounded to fit the circular defect, or the defect may be squared off to accommodate the angular flap. The surgeon may determine which of these modifications will yield the best aesthetic result.

Banner-type transposition flap

The finger-shaped flap is designed with a width that is equal to the width of the defect and a length equal to the distance from the pivot point to the far edge of the defect (see image below). The flap rotates in an arc about the pivot point. Although theoretically the flap can move through an arc of 180°, this is difficult to perform.

Unless the flap is based on an artery, this movement of 180° may produce a kink at the base of a random pattern flap that decreases the perfusion of the tip. Therefore, the flap typically is designed to rotate through an angle of 60-120° (see image above). As the flap is rotated and transposed, a protrusion often forms at the base of the flap (see image below).

This tissue redundancy (dog-ear) generated by the rotating motion should be removed. Care should be taken to remove the redundant tissue in a direction away from the pedicle of the flap such that the narrowing of the base of the flap does not compromise the blood flow to the flap, thereby affecting its viability (see images below).

Transposition island pedicle flap ^[25]

The design of the transposition island pedicle flap with a melolabial cheek donor site is such that a template is made of the defect and transposed onto the lower melolabial cheek. The distance between the lateral border of the defect and the template serves as the length of the island pedicle and should not be more than the defect width. If the length is longer, it impairs flap movement due to excess tissue at the point of transposition. The intervening skin between the flap and the template is excised partially, leaving a pedicle of subcutaneous tissue.

At the distal end of the flap, a full-thickness Burrow triangle is removed to facilitate closure of the donor area. Proximally, the pedicle is created, incorporating the subcutaneous tissue, deep muscle fibers, and vessel perforators to ensure flap survival through good vascular supply. The island flap is then transposed onto the defect by reflecting back the cheek skin at the point of transposition. The cheek skin is advanced medially and closed, eliminating the need to remove the proximal Burrow triangle.

For nasal sidewall and nasal ala defects, the sidewall acts as a donor site; the Burrow triangles are designed along the superior and inferolateral aspects of the defect. The island pedicle is created with the inclusion of the nasalis fibers to ensure vascularity. The secondary defect is closed by cheek advancement and primary closures of the Burrow triangles.

The major advantage of the transposition island pedicle flap is excellent color and texture match. The disadvantage, however, is the high incidence of trapdooring because, in these flaps, the proximal Burrow triangle is not excised and this may result in constriction of the surrounding flap causing the resultant trapdooring. This can be minimized to some extent by undermining the recipient site and placing tacking sutures if possible.

Subcutaneous pedicle Limberg flap ^{[26, 27, 28]}

This is an innovative refinement to the Limberg transposition flap that eliminates the dog ear and is useful in a variety of benign and malignant lesions of the face. The Limberg flap is designed near the defect with a 30-45°, and the width of the flap is approximately four fifths of the width of the defect. The distal part of the flap is elevated at the subcutaneous plane but over the mimetic muscle, and the proximal pedicle is then created as usual, incorporating the deep muscle fibers and vessel perforators.

A V-shaped incision limited to the immediate subdermis is performed at the pedicle of the flap, and this modification makes the Limberg flap a subcutaneous pedicle flap. The V-shaped incision is designed with a 45-60° angle so that this part of the donor site can also be sutured directly. In addition, further undermining around the V-shaped incision at the subdermal level, leaving the thick subcutaneous pedicle underneath, increases the mobility of the flap. This modified flap is of particular use in younger patients with restricted laxity of surrounding tissue.

Tunneled transposition flap ^[29]

This flap has 3 parts: (1) the inferior Burrow triangle, which is removed as a full-thickness, single-standing cone; (2) the donor site, which is to be completely matched to the primary defect; and (3) the superior Burrow triangle, which is excised to the dermis only because the underlying muscle and fat form the pedicle of the flap (see image below).

As with all transposition flaps, ensuring that the flap and the pedicle are of appropriate length is important. Therefore, the distance from the tip of the superior Burrow triangle to the end of the donor site is 5 mm greater than the distance from the tip of the superior Burrow triangle to the end of the defect (see image above). If the flap is taken more superiorly from the melolabial fold, then the pedicle will twist as it tunnels into the defect and compromise the blood supply to the flap; additionally, if it is taken too inferiorly, then a bulge would develop in the flap owing to the increased length of the flap.

The first step in the execution of the flap is to remove the superior Burrow triangle up to the dermis. Then, the inferior Burrow triangle and the flap donor site are separated from the surrounding skin and lifted at the level of the subcutaneous fat. The pedicle is then dissected such that the pedicle consists of the deep subcutaneous fat and the muscle fiber of the levator labii superioris alaeque nasi. The proximal portion of the pedicle should be thicker than 3-4 mm to ensure a good blood supply to the flap, and the distal portion should be up to 3-4 mm and not more, because this is the part of the pedicle that passes through the tunnel of the melolabial fold and the alar crease.

Now, both the donor and recipient site of the flap should be extensively undermined, which allows the secondary defect to be closed easily and it creates the tunnel between the primary and secondary defects. After this, the flap and the pedicle pass through the tunnel that was created. Sometimes it may be necessary to remove some fat from the tunnel for the pedicle to pass more easily and without compression. The donor site is closed primarily along the melolabial fold, and the inferior Burrow triangle is trimmed so as to suture the flap into the defect. This enables a pleasing aesthetic outcome because the alar crease is completely preserved.

Dehiscence

Primary dehiscence is due to incorrect construction of the flap such that there is excessive tension along the lines of closure. Secondary dehiscence is due to postoperative infection or bleeding (unrelated to the flap design or construction).

Flap necrosis

Flap necrosis may occur for a variety of reasons (eg, excessive tension, postoperative infection or bleeding, desiccation). Understanding the essential design and the pivotal restraining forces of transposition flaps is necessary to avoid problems. When the flap dynamics are understood and modifications are used to reduce tension on the tip, when required, complications are minimal.

Pincushioning, or the trapdoor phenomenon

This refers to the puffing up or out-pouching of a flap or graft above the surrounding skin surface and may occur in transposition flaps (see image below). ^{[30, 31]} It is seen more commonly with curvilinear flaps, such as the traditional banner and the double banner (bilobed) transposition flaps, because these allow more peripheral contraction than geometric flaps. Trapdooring also may occur because of such factors as excess subcutaneous fat under the flap, lymphedema (inferiorly based flaps offer better lymphatic drainage), oversized flaps, and a lack of contact inhibition (ie, failure to establish contact between the undersurface of the flap and the recipient bed), which allows contraction of the sides only and not the base, thereby pushing up the flap center.

The most important factor may be the process of scar contraction and maturation, which occurs at the periphery and base of the flap (see image below). If only the flap base contracts, the flap tissue is forced upward, creating pincushioning. The risk of puffing up or trapdooring can be minimized by avoiding the factors that may lead to it during the reconstruction of the flap.

See the list below:

• Use straight lines and geometric angles and avoid curvilinear lines wherever possible to minimize scar contraction.

• Undermine widely beyond the base of the flap. This cannot be emphasized enough. Wide undermining creates a uniform plane of scar contraction and, therefore, does not push the flap tissue up.

• Undersize the flap enough to prevent bunching up of the flap but not enough to cause tension on the line of closure because of the risk of flap necrosis.

• Maintain contact of the flap base with the recipient base to cause contact inhibition of flap contraction. If necessary (eg, if covering a concavity), this may be facilitated by the use of an absorbable suture from the base of the flap to the recipient bed oriented parallel to the direction of the blood flow.

• Orient or position the flap to allow good lymphatic drainage to prevent lymphedema. Inferiorly based flaps allow favorable lymphatic drainage.

• Use Z-plasty at the base of a transposition flap, such as rhombic flap, to enhance flap mobility, especially on the nose to prevent nasal tip and alar rim distortion. ^[32]

Minor corrections can be made through intralesional steroid injections, but surgical debulking is needed for major trapdooring.

A study by Lindsay and Morton of 21 patients indicated that alar wounds left by excision of small, penetrating carcinomas can be successfully repaired, and pincushioning avoided, by combining a skin graft with a subcutaneous fat transposition flap from the adjacent cheek. ^[33]

A study by Okland et al indicated that in bilobed transposition flap procedures for nasal reconstruction, thinning the flap by removing excess subcutaneous tissue can keep the rate of poor aesthetic results, revision, and pincushioning to a minimum. ^[34]

In conclusion, many variations and modifications of transposition flaps exist. Similar to other flaps, transposition flaps may be further modified and adjusted to accommodate individual situations. They may be lengthened or shortened, and their angles may be altered depending upon the availability and laxity of surrounding skin.

No single flap can be used to reconstruct all defects. Each patient must be treated with a unique strategy. A 2-dimensional picture of a given defect may seem to indicate a certain type of repair. This may or may not be the optimal repair for that given patient. Only by feeling the skin in the area around the defect may the best option for repair be determined.

Transposition flaps dissipate tension away from the flap apex and distribute it proximally, thus redirecting the tension lines and reducing the likelihood of anatomic distortion in the reconstructed area; this is a major advantage offered by the use of these types of flaps. Flaps designed in this manner allow improved contour by avoiding webbing, tenting across concavities, and bunching of skin laterally.

A significant degree of artistic ability and individual modification is required to consistently obtain optimal aesthetic and functional result.