33.6.1 Rhombic

c

Fig. 33.11 Bilateral rotation flap mucosal lip

Transposition flaps have several advantages over other closures. Their primary function is to redistribute and redirect tension. This is useful in the closure of defects which would otherwise close under high tension or distort a nearby anatomical structure leading to functional or aesthetic impairment. Transposition flaps are usually smaller than advancement and rotation

First described by Lindberg in 1963, the classic rhombic flap was designed to create a secondary defect perpendicular to the primary defect [18]. When closed, it would not only provide tissue to the primary defect but also redirect the tension vector by 90o. This allowed the primary defect to be closed under almost no wound edge tension. Subsequent modifications by Dufourmental and Webster provide more tension sharing between the primary and secondary defects. These modifications are useful in situations where some laxity around the primary defect is available [19]. (Fig. 33.12)

The classic Lindberg rhombic flap is designed by conversion of the primary defect into a four-sided parallelogram with each side of equal length and tip angles of 60° and 120° [18]. This rhombus forms the recipient site for the flap as well as the template on which to plan the flap incisions. In its classic configuration (Fig. 33.13), the incisions are designed by extending a line outward from one of the obtuse tips for a length equal to that of one side of the rhombus. From the free end of the extending line a second line is drawn parallel to one of the near sides of the rhombus, equal in length to that side. The tip angle in this configuration is 60°. The flap is lifted and transposed into place. The tension vector is redirected from that of closing the primary defect to that of closing the new secondary defect created in the design of the flap. This allows the tension vector to be shifted and redirected by 90°.

There are four possible flap designs off of the short axis of any rhomboid defect (Fig. 33.13). Which of these four flap configurations is selected depends on several factors that affect the outcome. A surgeon must consider adjacent anatomic structures and skin type, as well as the optimal location to place a scar.

The triangle of tissue redundancy created by the rotation of the transposition flap is removed by trimming a Burrow’s triangle at the pivot point. The trans-

posed tissue may be rounded to fit the circular defect, or the defect may be squared off to accommodate the angular flap.

As with any closure, understanding the tension forces is essential to the planning, execution, and outcome of the repair. There are two main tension forces associated with the classic rhombic flap. The first set of tension forces are realized during the approximation and closure of the secondary defect. The second set of

Fig. 33.12 (continued)

tension forces are generated at the tip of the flap when moving it into the primary defect. These forces are due to the resistance to rotation at the flap’s pedicle as well as shortening of the length of the flap during rotation into the recipient site. Dzubow describes these forces as pivotal restraint [16]. Securing the flap into the

recipient site under high tension is not advised because it may lead to tip ischemia and necrosis.

33.6.1.1 Dufourmental

The Dufourmental flap modification differs from the classic rhombic transposition flap (Fig. 33.14) in that it utilizes a narrower flap tip angle and a shorter arc of rotation, allowing easier closure of the secondary defect, and some sharing of the tension between the primary and secondary defects.

As with the classic rhombic flap, it is designed by extending the first line from the short axis of the rhomboid defect. However, the angle at which the first line is extended differs from the classic rhombic flap in that it bisects the angle formed by the first line of the classic rhombic flap (which extends straight out from the short axis of the rhombic defect) and the line formed by extending one of the sides of the rhombus from the same corner of the rhombus. The length of the first line is equal to that of a side length of the rhombus. The