Answer:
The dominant pedicle is the supratrochlear artery (terminal branch of ophthalmic artery), exiting the orbit superior to the medial canthal ligament, passing through the orbital septum, entering the glabellar region approximately 2 cm from the midline, and coursing cephalad beneath the frontalis muscle. The minor pedicle is the supraorbital artery exiting the supraorbital notch approximately 2.9 cm from the midline.
The entire middle third of the forehead will survive based on the dominant pedicle, however, flap width is limited to 2-3 cm (3-4 cm distally) by donor site closure. Flap length is determined by the frontal hairline. Usually 7-8 cm is adequate to reach the nasal tip. If the hairline is low, the flap can be oriented obliquely. Flap dimensions can be extended by preliminary flap expansion. The distal one-third of the flap is elevated superficial to the frontalis muscle and deepened to include the frontalis at the mid-forehead and the corrugator/procerus muscles at the glabella. The flap is rotated 180 degrees and inset directly or deepithelialized and passed under a skin bridge. If the donor defect cannot be closed primarily, it is allowed to heal secondarily. The pedicle is divided at a second stage.
The flap is very dependable. In fact, survival has been observed following division of both the supratrochlear and supraorbital vessels via connections to the angular, infratrochlear, and dorsal nasal arteries.