Local Flaps: Principles & Classification

Flaps are classified by their vascular supply into random pattern and axial pattern flaps. Random pattern flaps derive their blood supply from the dermal-subdermal vascular plexus without a named axial vessel. The vast majority of local cutaneous flaps used in dermatologic surgery are random pattern. Their survival depends on maintaining an adequate length-to-width ratio to ensure perfusion throughout the flap. Axial pattern flaps contain a named artery within their pedicle (e.g., paramedian forehead flap based on the supratrochlear artery). Because of their dedicated vascular supply, axial flaps can be longer and narrower than random pattern flaps.

The primary classification system for local flaps is based on the dominant tissue movement:

Understanding flap biomechanics is essential for predicting and managing the forces generated during tissue transfer. Tissue reservoir: every flap borrows tissue laxity from an adjacent donor area. The donor site must have sufficient laxity to close primarily after the flap is transferred. Preoperative assessment of tissue laxity (pinch test) in the planned donor area is critical. Pivot point: the point around which a flap rotates. As a flap rotates to fill a defect, its effective length shortens proportionally to the angle of rotation. A flap that measures 4cm when flat may only reach 3.5cm after 90 degrees of rotation due to this shortening effect. Tension vectors: flap closure generates closing forces that pull tissue in predictable directions. These vectors must be anticipated to avoid distortion of free margins (eyelids, lips, nostrils, ears). The surgeon must visualize where tension will ultimately resolve and ensure it does not cross or distort critical anatomic landmarks. Standing cutaneous deformities (Burow’s triangles): the redundant tissue mounds created by flap movement. These are the geometric price of tissue transfer and must be excised for a flat closure.

A rectangular or trapezoidal flap that slides forward along its long axis to cover an adjacent defect. Burow’s triangles are excised at the base of the flap to facilitate movement and prevent standing cones. Design: the flap width matches the defect width. Length is determined by the distance needed to advance plus compensation for tissue stretch. Burow’s triangles are planned at the lateral base of the flap. Best applications: forehead (horizontal laxity allows significant advancement), temple, helical rim, upper lip (perialar advancement).

Two opposing advancement flaps that move toward each other to close a central defect. The resulting scar forms an H or T shape. Design: incisions extend laterally from both ends of the defect, creating two rectangular flaps that advance medially. Burow’s triangles are excised at the corners. Best applications: central forehead (bilateral flaps recruit laxity from both sides), scalp vertex, central lip. The bilateral design distributes tension evenly, reducing the risk of distortion.

The V-to-Y flap is a triangular island of skin that advances on a subcutaneous pedicle. The flap is completely incised around its perimeter but remains attached to the underlying subcutaneous tissue, which provides both blood supply and the pushing force for advancement. Design: draw a V-shaped incision with the apex pointing away from the defect. Incise the skin and dermis, then free the flap from the surrounding tissue while preserving its subcutaneous pedicle. Push (do not pull) the island toward the defect. Close the donor site primarily, converting the V into a Y. Best applications: nasolabial fold defects, lip reconstruction (vermilion advancement), cheek defects near the alar base.

A rotation flap is a semicircular flap that pivots around a point to fill an adjacent triangular defect. The defect is conceptualized as a triangle, and the flap arc sweeps from one side of the triangle. Design principles: the arc length should be 4–8 times the diameter of the defect to distribute tension and minimize closure forces. A back-cut at the base of the flap increases mobility but shortens the effective pedicle width. An alternative to the back-cut is excision of a Burow’s triangle at the flap base. Best applications: scalp (large rotation flaps up to 15–20cm can close significant defects), cheek, temple. The scalp is the ideal location for rotation flaps because the subgaleal plane allows extensive undermining.

The classic rhombic flap (Limberg design) is one of the most versatile and commonly used transposition flaps in dermatologic surgery. It converts a circular defect into a rhombus (parallelogram with 60° and 120° angles), then transfers an adjacent rhombic-shaped flap to fill it. Design: the defect is converted to a rhombus with 60° and 120° angles. The short diagonal of the rhombus is extended from one of the 120° corners, and a line of equal length is drawn parallel to the adjacent side of the rhombus. This creates the flap. Four possible orientations exist for every rhombic defect. The surgeon selects the orientation that: (1) recruits tissue from the area of greatest laxity, (2) places maximum tension along the closure line rather than perpendicular to it, and (3) avoids distortion of free margins. The Dufourmentel modification allows angles wider than 60°, expanding the applicability of rhombic flaps to defects that do not conform to the standard 60° geometry.

The bilobed flap is a double transposition flap originally described by Esser (1918) and modified by Zitelli (1989) to reduce standing cutaneous deformities. It uses two lobes: the primary lobe closes the defect, and the smaller secondary lobe closes the primary lobe donor site. The secondary lobe donor site is closed primarily. Zitelli modification: total arc of rotation is 90–100° (compared to Esser’s original 180°). The primary lobe is equal to the defect diameter, the secondary lobe is approximately 75–80% of the primary lobe diameter, and each lobe is separated by 45–50°. This is the gold standard flap for nasal tip and alar defects less than 1.5cm in diameter. The nose has limited tissue laxity, and the bilobed design distributes the tissue recruitment across two donor sites, each requiring less individual tissue movement.

The Z-plasty is a transposition of two triangular flaps that changes the direction of a scar and can lengthen a contracted scar. The central limb is the existing scar or planned scar line, and two limbs of equal length are drawn at the ends at specified angles. The classic Z-plasty uses 60° angles, which provides approximately 75% lengthening. Smaller angles (30–45°) provide less lengthening but less tissue disruption. Larger angles (75–90°) provide more lengthening but may not close primarily. Multiple small Z-plasties in series are preferred over a single large Z-plasty for long scar revisions. They distribute the change more evenly and create a less conspicuous zigzag pattern.