Transposition Flaps

Transposition flaps differ fundamentally from advancement and rotation flaps in that the flap is lifted over intervening intact skin to reach the defect. This "bridge" of normal tissue between the donor site and the defect is the defining characteristic. The biomechanical advantage of transposition is the ability to redirect the vector of wound closure tension: the primary tension shifts from the defect itself to the donor site, which is chosen in an area of greater tissue laxity or where the resulting scar will be better camouflaged. Transposition flaps are subject to pivotal restraint, similar to rotation flaps, because the flap must pivot around its base to reach the defect. The effective reach of the flap shortens as the angle of transposition increases, so the flap must be designed longer than the straight-line distance to the defect. Understanding the geometry of each transposition variant is essential for predictable results.

Transposition flaps encompass a broad family of designs ranging from the simple Z-plasty to the geometrically precise rhombic flap. The table below summarizes the major variants, their design principles, and optimal clinical applications.

The Z-plasty is the prototypical transposition flap, consisting of two triangular flaps that are interdigitated (swapped). A central limb crosses the scar or contracture to be revised, and two lateral limbs extend at equal angles from each end of the central limb, creating a Z-shaped design. When the two triangular flaps are transposed, the central limb reorients by twice the angle of the lateral limbs, and the scar lengthens proportionally. The degree of lengthening and reorientation depends on the angle: 30-degree limbs produce 25% lengthening, 45-degree limbs produce 50% lengthening, and the classic 60-degree limbs produce 75% lengthening with a 120-degree reorientation of the central limb. Z-plasty is invaluable for releasing scar contractures, reorienting unfavorable scars into relaxed skin tension lines, and breaking up linear scars into a less conspicuous zigzag pattern. Multiple small Z-plasties in series can be used along a long scar for a more natural result.

The classic rhombic (Limberg) flap is based on the geometry of a rhombus (parallelogram) with 60-degree and 120-degree angles. The defect is converted to this rhombic shape, and the flap is designed as an extension of one of the short diagonals. The first incision of the flap extends from one corner of the rhombus in the direction of the short diagonal, equal in length to one side of the rhombus. The second incision angles parallel to the adjacent side of the rhombus, also equal in length. The resulting flap is transposed into the defect, and the donor site is closed primarily. Because a rhombus has four possible short diagonal extensions, there are four possible flap orientations for any given defect. The optimal orientation places the maximum tension vector along an axis of greatest tissue laxity and directs the final scar lines into favorable locations (relaxed skin tension lines or cosmetic subunit boundaries). The rhombic flap is particularly effective on the medial canthus, upper nose, temple, and cheek.

The bilobed flap consists of two transposition flaps arranged in succession on a shared pedicle. The first lobe transposes into the primary defect, and the second (smaller) lobe transposes into the donor site of the first lobe. The tertiary defect (the donor site of the second lobe) is closed primarily. The Zitelli modification standardized the design: the total arc of transposition is 90 to 110 degrees (compared to the original 180 degrees), with each lobe transposed approximately 45 to 55 degrees. The first lobe is designed equal in width to the defect, and the second lobe is narrower (approximately 60-80% of the defect width), as it recruits tissue from a progressively more lax area. The bilobed flap is the workhorse for defects of the distal lower third of the nose up to approximately 1.5 cm in diameter, where tissue is relatively inelastic and alternative donor sites are limited.

The nasolabial (melolabial) transposition flap recruits tissue from the medial cheek, transposing it across the melolabial fold onto the lateral nasal sidewall or alar region. The flap is designed with its base at the melolabial fold and its long axis oriented along the fold or within a relaxed skin tension line of the cheek. The cheek donor site is closed primarily, taking advantage of the substantial laxity of cheek tissue. The nasolabial transposition provides excellent color and texture match for nasal skin because the medial cheek skin is similar in thickness, color, and sebaceous quality. This flap is particularly useful for defects of the lateral nasal sidewall and alar region measuring 1 to 2 cm. The scar along the melolabial fold is typically well camouflaged. A potential drawback is blunting of the alar crease if the flap is too thick or if it is inset without recreating the crease.

The banner flap is a narrow, pedicled transposition flap designed as a long, thin triangle or rectangle. It is transposed over intervening tissue to fill a small, typically circular defect. The banner flap is useful for small defects (0.5 to 1 cm) where a simple linear closure would create unacceptable distortion, particularly on the nasal sidewall, periorbital region, and eyelid. The narrow design minimizes donor site morbidity, and the donor site is closed primarily. The pedicle is typically based on the side of maximal tissue laxity, and the flap is transposed into the defect, with the standing cone at the base excised to facilitate inset.

Transposition flap complications include trapdoor (pincushioning) deformity, distal flap necrosis, standing cone deformity, donor site scar widening, and distortion of adjacent structures. Trapdoor deformity is the most common complication of all transposition flaps and results from scar contracture of the circumferential border of the flap, lymphatic disruption, and excessive subcutaneous tissue. Prevention includes thinning the flap to the dermal-subdermal junction (where safe), wide undermining around the entire defect and flap, and precise wound edge eversion. Treatment of established trapdoor includes intralesional triamcinolone acetonide (10-40 mg/mL) at 4 to 6 week intervals and, if unresponsive, surgical revision with scar release and flap thinning. Standing cone deformities should be excised at the primary surgery whenever possible.