One-sized bilobed flap does not fit all standing cones: a mathematical analysis of the standing cone in bilobed flap dynamics

The bilobed flap (BLF) is a workhorse for nasal repair. Alterations to the length and orientation of the BLF's standing cutaneous deformity (SCD) have been suggested as a means of preventing Z-plasty-induced flap lengthening and consequent ipsilateral alar depression. To investigate the effect of design variations of the SCD on bilobed flap mechanics. Geometric analysis of the BLF was performed using commercially available graphing software. BLFs were designed with a SCD equal to one radius (rBLF) and one diameter (dBLF) of the primary defect as well as with a more superiorly-oriented one diameter SCD (soBLF). Lengths from the pivot point to the distal edges of the primary defect and primary lobe were measured and compared. Elongation or a more superior orientation of the SCD without changes to the rest of the flap design forms a primary lobe along a shorter arc resulting in insufficient flap length to resurface the primary defect. The insufficient length requires secondary motion to complete the repair and possible unintended alar displacement. Modification of the size and orientation of the SCD alters the location of the pivot point, which is a key determinant of BLF mechanics. Therefore, changes to the SCD require alterations to the remainder of the flap design to ensure aesthetic and functional success.