The Bilobed Flap - Critical Analysis and New Mathematically Precise Design.

Background: A bilobed flap is a workhorse flap to reconstruct the lower third of the nasal defect. It has been described as a double transposition flap. Various changes have been proposed to reduce the drawbacks of this flap. Most of the modifications pay attention to flap width and length without emphasizing the pivot point. In this article, the classic Zitelli design is tested for its mathematical precision, and the key role of the pivot point is discussed. Method: The bilobed flap was designed with accurate mathematical measurement on simple drawing software. Its design and flap movement were studied and critically analyzed. The biogeometry of the flap was investigated with multiple diagrams and various mathematical principles. Results: The classic description carries some mathematical errors. The author describes a new design that is more precise mathematically. A proper pivot point location is vital for accurate design and flaps movement. Putting the pivot point at a distance 2.6 times the radius of the defect makes the movement of the flaps precise. In a proper design, the extension of secondary flap length is an optional step, and the dog-ear so formed can be tackled separately. This new design of the bilobed flap only needs rotation advancement movement. Conclusions: The bilobed flap is one of the major tools for lower third nasal reconstruction. A perfectly designed bilobed flap is primarily a rotation flap. A slight modification of classic design by putting the pivot point at a distance 2.6 times of the radius of the defect makes it more perfect mathematically.