A transposition flap is elevated from an area of laxity, lifted over an adjacent area of tissue, and transposed into an operative wound. Even more so than with rotation, transposition flaps accomplish tension redirection and redistribution.1 Adjacent laxity is tapped into to mobilize and transfer tissue from an area of laxity to an area of “need.” Transposition flaps are able to redirect tension vectors completely perpendicular to the needed primary motion of the repair, and as such can literally push tissue into a wound in order to avoid tension on a crucial structure or free margin. The prototype of this flap group is termed the rhombic design.2–7 Other commonly utilized transposition flaps include the banner or unilobed flaps such as the single-staged nasolabial flap, the bilobed flap, the trilobed flap, and the 30° angle flap.
Transposition flaps are often able to close an operative wound with a smaller reconstruction than a rotation or advancement. The lines from transposition flaps tend to be broken up and multidirectional. This can be either an advantage or a detriment, depending on the application. In areas of great convexity such as the repair of a defect along the jaw line, the shift in direction of a transposition flap can ameliorate the transition over a sharp protuberance. In areas of concavity such as in the medial canthus, the Z-shape of a transposition flap can redirect tensions and prevent tenting and web formation. Elsewhere, however, such as on the mid cheek, a transposition flap can leave a complex geometric pattern that can be highly distracting.
A transposition flap is, in essence, a logical modification of a rotation flap. The donor site for a transposition acts much as a back cut, and the flap transposes by rotational motion on a pedicle at its base. The same principles apply to transposition, and some of the same oversizing modifications discussed in Chapter 3 are applied herein.
Although this is not a historical text, it is worth reiterating the contribution of Alexander Limberg who in 1963 published a treatise on the repair of rhomboidal surgical wounds with rhombic transposition flaps. Although in practice, there are some deficiencies in the Limberg design of the classic rhombic transposition, its development was at the forefront of modern surgical reconstruction and stands as a great achievement in the field of reconstructive surgery.
RHOMBIC FLAP BIOMECHANICAL DESIGN
The classic rhombic flap (Fig. 4.1) is constructed around a geometric four-sided defect of equal side length, and tip angles equal to 60° and 120°. It is formed by extending the short diameter of the defect beyond the flap for a length equivalent to one of the sides. The flap is then created by drawing a line from the free end of the extended short diameter, parallel to one of the ...