The Super Thin External Pudendal Artery (STEPA) Flap. A Study Investigating The Thinnest Flap Described to Date

Background: The need for improved microsurgical reconstructive techniques is ongoing given the “ideal” free flap still does not exist. When reconstruction requires a thin flap, options have remained limited and flaps with minimal donor site morbidity that do not require secondary de-bulking have been elusive thus far. The importance of a thin and supple flap cannot be understated when dealing with challenging cases such as the dorsum of the hand or foot, the head and neck or over joints. The authors propose a previously un-described free tissue transfer based on the external pudendal artery that fulfills many of the aforementioned goals. An anatomical cadaveric study has been performed describing the super thin external pudendal artery (STEPA) flap.

Material and Methods: Six fresh cadavers were used in the raising of eight hemiscrotal flaps and two bipedicled scrotal flaps based on the external pudendal vessels. Two unipedicled and both bipedicled flaps underwent cannulation of the external pudendal artery followed by injection of an iodinated contrast medium, iohexol (Omnipaque) and three-dimensional computed tomographic angiography to evaluate vascular anatomy. Colored-latex was injected into one raised hemiscrotal flap. Measurements were made on the cadaveric dissections and on a computed tomography workstation.

Results: The average external diameter of the external pudendal artery measured 2.81mm at its origin from the femoral artery, the vein 4.44 mm. The mean pedicle length measured 11cm (range, 10 to 12 cm). The mean thickness of the flap measured 1.1mm.

Conclusions: A new free flap, the STEPA flap, has been described that is the thinnest myocutaneous free flap with over 80% of the thickness of the flap less than 1.1mm. It has been demonstrated to have reliable anatomy with more than adequate vessel caliber. It has a large surface area and a generous pedicle length for free tissue transfer. Donor site morbidity is favourable. It is accepted that there may be cosmetic issues regarding flap pigmentation and a variable degree of hair in patients where the reconstruction is visible. We contend that there exist many successful techniques which address pigmentation and depilation, and that this trade-off is acceptable given the functionality and characteristics of this uniquely thin flap. It has the potential to be used in many clinical scenarios where thin supple reconstruction is a high priority.