Rhombic and Rhomboid Schwenklappen-Plasty

EDITORIAL COMMENT

The reader will find this chapter difficult to assimilate. The mathematics are correct and helpful in the planning of flaps; however, one should realize that the skin is an elastic tissue, but with varying degrees of elasticity, depending on anatomic location and age of the patient.

The term Schwenklappen comes from the German schwenken, meaning “to move, swing, or turn about.” Whereas a transposition flap rotates only about a pivot point, a Schwenklappen flap not only rotates about a pivot point, but the reserve skin adjacent to the base slides in the direction of the rotation as the flap donor site is closed (1, 2, 3, 4). (Note that a rhombus, e.g., a Limberg flap, is an equilateral parallelogram, with all four sides equal, whereas a rhomboid is an oblong parallelogram, with only opposite sides and angles equal.)

INDICATIONS

Rhombic and rhomboid Schwenklappen-plasties can be applied in any region of the body if blood supply, skin reserves, and the need for flap delay are taken into account. One of their advantages is that the optimal use of existing skin reserves can easily be calculated. These flaps are especially suited for skin defects in the face and on the neck because of the good blood supply found in these areas. In other regions, flap design and flap delay also can favor their application.

Skin defects should be closed under minimum tension by making use of available skin reserves. This includes mobilization of defect margins for diminishing the size of the primary defect, extension of the flap itself (pure advancement or extension flaps), extension of the surrounding skin of the donor area (pure Schwenklappen-plasties), and no extension of skin at all (pure transposition flaps). Figures 100.1, 100.2, 100.3, 100.4 illustrate the ease with which Schwenklappen-plasties may be performed in various combinations with other techniques for covering skin defects when skin reserves are minimal.

FLAP DESIGN AND DIMENSIONS

Planimetric Schwenklappen-Plasties

Planimetric Schwenklappen-plasties are flaps that involve only two dimensions of the skin; stereometric Schwenklappen-plasties use three dimensions, creating curved surfaces.

For these flaps, the shapes of rhombi (Limberg, Fig. 100.5A) and rhomboids (Roggendorf, Fig. 100.5B) provide skin-saving incisions, since Burow’s triangles are included in the flap design. Primary closure of the donor area is a prerequisite for Schwenklappen-plasties. As the donor area is closed, the flap base is rotated; as a result, the flap transfer is effected. Tension is thus shifted into the suture line of the flap donor area. With exact planning, therefore, the flap itself can be transferred into the defect without any tension.

The skin reserve r must be equal to or greater than the required skin extension s. Planning of planimetric Schwenklappen-plasties is simplest if small circular defects are to be covered by rhombic flaps with angles between 60 and 70 degrees. Whatever the direction of extension, the skin extension vector s can be planned in line with the maximum skin reserve vector r_max without any difficulty (Fig. 100.6).

In oblong skin defects, the skin reserve will lie mostly in the direction of the long axis of the primary defect, and here too rhomboids with angles α of 60 to 75 degrees are best (Fig. 100.7A). These rhomboids can be constructed easily using the angle α plus the width and length of the defect.

If skin reserve is smaller than required skin extension (that is, r < s), the maximum skin reserve vector r_max should be determined and the skin extension vector s planned in that direction.

The mutual dependence between Schwenkungs-angle α and the direction of skin extension s (Fig. 100.7A) makes it possible to calculate the ideal angle α for planimetric Schwenklappen-plasties by using the formula α = 2 (90 + δ)/3 (Fig. 100.7B). This formula can be applied in rhomboid as well as rhombic planimetric Schwenklappen-plasties.

Stereometric Schwenklappen-Plasties

As has been pointed out, the direction of the skin extension vector s depends on the transfer angle α in planimetric Schwenklappen-plasties (Fig. 100.7A). This leads to a limited applicability of planimetric Schwenklappen-plasties in difficult reconstructions; however, when a stereometric

Schwenklappen-plasty with additional transposition is used, better results are obtained (Fig. 100.1C).

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