RHOMBIC FLAPS

INTRODUCTION

Ever since the advent of Mohs’ micrographic surgery for the treatment of cutaneous malignant neoplasms, complex surgical defects of the head and neck have become increasingly challenging to repair with an acceptable functional and aesthetic result. Primary wound closure for many skin defects is impossible; thus recruitment of adjacent tissue is often required for repair. Over the years, careful study and practice have yielded a wealth of techniques and methods to aid the reconstructive surgeon in the repair of facial cutaneous defects. The appropriate use of local and regional cutaneous flaps to achieve wound closure with minimal distortion of surrounding facial landmarks is a hallmark of a well-trained plastic surgeon.

Although no single skin flap will provide the optimal repair for every defect, the rhombic flap has long been considered a workhorse in the armamentarium of the reconstructive surgeon. Its application is wide, with the ability to repair variable-sized defects of the cheek, scalp, neck, temple, nose, chin, and eyelid. This is in large part because of the simplicity of the flap design and the reliability with which it may be used to reconstruct cutaneous defects. The resultant scars and tension vectors are predictable and well defined, and there is generally little tension on the surrounding tissues. Furthermore, rhombic flaps have been shown to exhibit a higher degree of tissue conservation than primary linear closure (with excision of standing cutaneous deformities [SCDs]) and other commonly used local flaps.

The rhombic flap is a transposition flap, such that the mobilized tissue pivots toward the defect ( Fig. 11.1 ). There is also minimal advancement of the flap for the flap to extend to the most distal corner of the defect. As a random vascular patterned flap, it is dependent on its dermal and subdermal plexus for survival until neovascularization occurs. Thus care must be taken when raising and transferring the flap to ensure the vascular plexus is not injured. Aesthetic outcomes and complication rates using rhombic flaps are similar to those seen with the use of other local flaps of the head and neck. Nevertheless, a recent analysis of 446 Mohs defect repairs, albeit by a single surgeon, suggests a slightly higher rate of trap-door deformity and need for postoperative corticosteroid injection when using rhombic flaps compared with other methods of repair.

The first rhombic transposition flap was initially described by Alexander A. Limberg in 1946, who later published his description in 1963. On the basis of extensive work with paper models, Limberg described the use of a rhombic transposition flap with internal angles of 60° and 120° to cover a rhombus-shaped surgical defect with corresponding internal angles and defect borders of equal length to the borders of the flap. If the cutaneous defect did not have this configuration, additional skin was removed to create the rhombus. Today, a rhombus-shaped transposition flap that is true to Dr. Limberg’s original design with internal angles of 60° and 120° is commonly referred to as a Limberg flap . The flap described by Limberg had some limitations, however, which gave rise to a number of variations, including those designed by Dufourmentel and Webster. ^, These modifications addressed issues of wound closure tension, SCDs, and the practice of discarding healthy skin to create a rhombus-shaped defect. In 1962, Dufourmentel expanded on Limberg’s model and described a method to close any rhombus-shaped defect, regardless of internal angles. In 1977, Webster published another significant modification of the Limberg flap, in which he used a narrower 30° angled flap coupled with a W-plasty at the flap’s base to facilitate wound closure. This design allowed for less sacrifice of normal tissue with more evenly distributed tension across the wound to achieve repair of a defect. Since the 1970s, multiple modifications have been further described, including the use of multiple rhombic flaps to close large or complex defects and the coupling of Z-plasties with rhombic flaps to expand the base of the flap.

Selecting a rhombic flap donor site requires a systematic approach to ensure an aesthetic and functional result. Mobile structures such as the eyelid, lip, and melolabial fold must be accounted for when designing local flaps. Care is taken to avoid distortion of these structures resulting from unfavorable vectors of wound closure tension or scar trajectories. ^, When designing a rhombic flap, an area of skin with adequate tissue laxity for flap harvest is identified. Pinching the skin adjacent to the defect at the proposed donor site of the flap can help determine whether there is adequate tissue laxity for closure of the donor site. A careful evaluation of relaxed skin tension lines (RSTLs), lines of maximal extensibility (LME), and aesthetic boundaries must occur to plan incisions that will maximize scar camouflage and minimize wound closure tension. ^, Additionally, the surgeon must anticipate resultant scars and all vectors of tension after transfer of a planned flap to ensure appropriate flap selection and orientation .

LIMBERG FLAP

When designing a Limberg flap, the defect is modified to create a rhombus-shaped defect with internal angles of 60° and 120°. The 60° and 120° rhombus may be thought of as two 60° equilateral triangles aligned base to base. Thus all sides of the defect are of equal lengths, which are in turn equal to the short diagonal of the defect. To design a Limberg flap, the line of the short diagonal of the defect is extended, bisecting one of the internal 120° angles. The line is extended a length equal to the short diagonal. This creates the first side of the flap. The second side of the flap is designed by marking a second line of the same length as the first, parallel to the adjacent side of the rhombic defect, creating a 60° angle at the flap’s apex ( Fig. 11.2 ). The designed flap is precisely equal in size to the defect. Four possible rhombic flaps can be designed for any rhombus-shaped defect. ^,

After transfer of a Limberg flap, the point of greatest wound closure tension is at the donor site. ^, This tension vector runs roughly parallel to the adjacent border of the primary defect, and there is relatively minimal tension across the other portions of the wound. This is an important consideration when designing and orienting the flap to minimize distortion of surrounding tissues. The vector of maximal wound closure tension should run parallel to the LME in that region of the face. The scar that results from the Limberg flap is highly predictable and consists of straight, precise lines that run along three or more distinct axes. It is therefore impossible to situate all portions of the scar within existing RSTLs ( Fig. 11.3 ).

The Limberg flap has been used to repair defects of the cheek, temple, eyelids, nose, lip, chin, and neck ( Fig. 11.4 ). The horizontal parallel furrows of the forehead make this region of the face particularly unsuitable for use of rhombic flaps. Disadvantages of the Limberg flap include the formation of an SCD and the need to discard normal skin to convert the defect into a 60° to 120° rhombus. In addition, at least one portion of the resultant scar will lie outside of RSTLs, and thus scar camouflage may not be as good as alternative flaps.

DUFOURMENTEL FLAP

The Dufourmentel modification of the Limberg flap was introduced as a method of broadening the application of the rhombic flap to allow for reconstruction of more square-shaped defects with less discarded tissue. The Dufourmentel modification lacks stringent rules regarding the flap’s internal angles, thus allowing for greater versatility than the original Limberg design. Although both flaps require all sides of the defect to be equal in length, the length of the short diagonal in the Dufourmentel flap will vary based on the acuteness of the internal angles of the defect.

To design the flap, two lines are created. The first line is an extension of the short diagonal of the defect, and the second is an extension of one side of the defect. The angle created by these two lines is bisected by a third line to create the first side of the flap, which is equal in length to the sides of the defect. The second side of the flap is drawn parallel to the long diagonal of the defect and is also equal in length to the sides of the defect ( Fig. 11.5 ). ^, The Dufourmentel flap has the advantage of a lesser arc of pivot, thus creating a smaller SCD than is observed with the Limberg flap. Like the Limberg flap, the Dufourmentel flap must be oriented with the vector of greatest tension parallel to the LME. The flap fits the defect exactly, thus minimizing tension and distortion of tissue surrounding the defect. As with the Limberg flap, not all lines of the resultant scar will fall within RSTLs (see Fig. 11.5 ).

WEBSTER 30° FLAP

Initially described in 1978, the Webster 30° flap uses two modifications in an attempt to promote greater tension sharing between the closure of the defect and the flap donor site and to minimize the size of SCDs that necessitate excision of normal tissue. First, the flap is narrower compared with the Limberg flap design. The flap has a 30° apex, allowing for easier closure of the narrower donor site and for transposition of the flap to the defect with the creation of a smaller SCD. ^, Second, a W-plasty is incorporated adjacent to the base of the flap, which also minimizes wound closure tension and the formation of an SCD ( Fig. 11.6 ).

The Webster 30° flap, also known as the 30° rhombic flap , is designed by approximately halving an equilateral triangle. The triangle is designed with a height equal to the length of one side of the defect. The angle of the apex of the transposition flap is 30°. The width of the base of the flap is half the greatest width of the defect. The Webster 30° transposition flap allows a more even distribution of wound closure tension but has greater potential to distort neighboring structures. This is because the surface area of the flap is less than the surface area of the defect that the flap is designed to repair. Thus secondary tissue movement is necessary to assist the flap with closure of the primary defect. Furthermore, care must be taken to ensure that the angle created between the flap and the adjacent side of the defect is at least 110°. A lesser angle may result in vascular compromise of the repair. The Webster modification results in an irregular closure line because of the W-plasty with an additional limb of scar (see Fig. 11.6, D ).