LAUSR

It was recently demonstrated that rotation flaps are curvilinear advancement flaps and do not rotate [1]. Transposition flaps, however, are flaps that do rotate on the surface plane of the body. The verb Btranspose^ means to change something from one position to another, or to exchange the positions of two things. In a surgical context, it means that the position of tissue is changed by an operative procedure (nerve transposition, vessel transposition, skin transposition). The term Btransposition^ was used as early as 1855 by Denucé, as a general term for local skin transfer (Btransfer^ being the currently preferred term) [2]. The term Btransposition flap,^ to describe a skin flap that rotates around a pivot point in the base of the skin pedicle to close an adjacent skin defect, became popular in the 1970s. In geometrical terms a pivot point is the center point of any rotational system [3]. In surgical terms, it is the center of the arc aroundwhich a flapmoves during its transfer [4]. This concept is easy to understand for an axial pattern flap where the pivot point is (almost always) the identifiable vascular pedicle in the base of the flap. However, in a random pattern skin flap, it is different. In a random pattern transposition flap, the pivot point is usually depicted to be the point furthest from the apex of a defect. This Bclassic^ transposition flap is designed as a relatively large flap which is moved laterally with a fixed pivot point at the base of the flap, situated furthest from the adjacent, triangularized defect (Fig. 1; left) [5].We would call this a contralateral pivot point. Not all transposition flaps have a contralateral pivot point. One of the best-known transposition flaps is the rhombic flap of Alexander Limberg (Fig. 2). This flap rotates around a pivot point that coincides with the defect: an ipsilateral pivot point. The donor defect is closed by advancing the contralateral base of the flap from A to C. A prerequisite for this procedure is that there is enough slack skin to advance the contralateral base of the flap over the length of one side of the rhombus to close the defect. The LLL-flap of Dufourmentel [6] and the oblong parallelogram-shaped or BSchwenklappen^-plasty of Roggendorf [7], both variations of the Limberg flap, similarly have an ipsilateral pivot point. The location of the pivot point of a Limberg flap is still graphically portrayed by some [8] to be on the contralateral side of the defect, which is clearly wrong. In the well-established literature onemay also encounter the depiction of a contralateral pivot point, which clinically then proves to be ipsilateral. Figure 3 (above) shows a schematic representation of a nasolabial flap to cover a labial defect, as proposed by McGregor and McGregor [9]. To close the donor defect of a nasolabial flap, the skin of the cheek is commonly undermined. Sufficient skin laxity will ensure that the closed donor defect lies more or less in the original nasolabial fold. During this process, the contralateral base of the flap moves towards the fold, as depicted in Fig. 3 (middle and low). The contralateral and ipsilateral pivot points are the extremes of a spectrumof pivot points aroundwhich transposition flapsmay rotate. It is not only the geometrical shape of the defect and the design of the flap that determine the ultimate location of a pivot point but also the reserve or laxity of skin in the donor area. Availability thereof will permit advancement of the contralateral base of the flap. In a properly planned Limberg flap, this will happen with the acme of mathematical grace that accompanies this method. In a transposition flap in which the contralateral base can be partly advanced towards the defect, the pivot point will be found between the two extremes: that of the contralateral pivot point in the Bclassic^ transposition flap and that of the ipsilateral pivot point of Limberg’s rhombic flap. Knowledge at the outset about the position of the pivot point has clear implications for the planning of a transposition flap. If the donor defect of a transposition flap can be closed by advancing skin from the area at the contralateral base of the flap, the pivot point will shift in the direction of the ipsilateral base of the flap. Hence, a shorter flap than * Klaas W. Marck [email protected]