The supratrochlear artery leaves the orbit at the medial end of the brow, roughly two centimetres from the midline, and climbs vertically toward the hairline. McCarthy et al. (1985) showed that the flap is supplied through a rich anastomotic network around the medial canthus and can survive on a base extended below the brow. Shumrick and Smith (1992) traced the artery from a deep position over the corrugator, through the frontalis, to a subcutaneous course in the upper forehead, and Reece et al. (2008) confirmed this pattern with dynamic imaging. Two design rules follow from these studies. The pedicle can be made narrow provided it is centred on the vessel, and the distal flap, where the artery lies just under the skin, can be thinned with more safety than the proximal part.

The nose is seen as a set of convex and concave surfaces bounded by shadows. Burget and Menick proposed that when most of a convex subunit such as the tip or ala is lost, replacing the whole subunit places scars in the natural borders and lets the flap contract into a rounded form (Burget and Menick, 1985). Rohrich et al. (2004) argued from a large series that the rule should be applied flexibly and that healthy tissue need not always be discarded. Both positions accept that contour, not scar position alone, determines whether a nose looks normal.

Lining and support matter as much as cover. Lining may come from hinged septal mucoperichondrial flaps, from skin turned in from the defect margin, from a skin graft, or from the folded distal end of the forehead flap itself (Burget and Menick, 1989; Menick, 2010). Cartilage must be placed along the nostril rim even where none exists in the normal nose, because an unsupported flap contracts upward and inward as it heals. Alternatives to the forehead for smaller defects, such as the bilobed flap (Zitelli, 1989), are outside the present scope, and the choice among methods by size and site is reviewed by Park (2000) and Thornton et al. (2008).

Reconstruction should not begin until the wound is ready. After tumour excision this means confirmed histological clearance, and after trauma or infection a clean, stable bed. The defect is then described layer by layer and subunit by subunit on a standard diagram: which skin is missing, whether the alar cartilages, upper lateral cartilages or septum are deficient, and how much lining has gone. The forehead is inspected for scars that cross the intended pedicle and for the height of the hairline. Factors that the literature links with flap complications, of which smoking is the most consistently reported (Little et al., 2009), are recorded and discussed. Consent covers the number of operations, the weeks spent with a visible pedicle and the forehead scar.

A written plan names the source of each layer. For lining, the choice depends on the size of the lining defect and on whether the septum is intact. For support, septal cartilage is preferred for straight struts, conchal cartilage for curved alar grafts, and rib where large amounts are needed. For cover, the surgeon decides whether to enlarge the defect to a full subunit, weighing the two positions described above.

An exact template is essential. Where the opposite side of the nose is intact, a pattern of the normal ala or hemi-tip is made in foil or suture-pack material and reversed; where it is not, the pattern is made on a model or on the reconstructed framework. The template is three-dimensional when formed and is flattened before transfer to the forehead, so that the flap is neither too small, which distorts the nostril, nor too large, which leaves a bulky result. The pedicle side is chosen with a Doppler probe, and the reach is checked with a length of gauze swung from the pivot point at the medial brow.

Lining is established first, then primary cartilage grafts where the lining is vascular enough to carry them. The flap is outlined from the flattened template with its axis vertical over the Doppler signal and its pedicle a little over one centimetre wide. In the three-stage method the flap is raised with all its layers, including frontalis, and is not thinned at this operation (Menick, 2009). The traditional two-stage alternative thins the distal flap at transfer and divides the pedicle about three weeks later (Boyd et al., 2000). The protocol asks the surgeon to choose between them in advance and to record the reason: the three-stage sequence for defects needing folded lining, extensive cartilage work or transfer in a smoker, and the two-stage sequence for limited defects in favourable tissue. The forehead is closed directly as far as it will come, and any gap near the hairline is left to heal by secondary intention.

The weeks between operations are part of the method. The raw undersurface of the pedicle is dressed or covered with a thin skin graft to limit oozing, the nasal airway is kept clear of crusts, and the colour of the flap is inspected at each dressing. Spectacles must not rest on the pedicle. Abstinence from tobacco and nicotine is asked for throughout the staged sequence, and the request is repeated at every visit, since the flap is most at risk at the operations still to come.

About a month after transfer the flap is lifted again from the nose, leaving its pedicle intact. Because both the pedicle and the healed distal inset now nourish it, the skin can be elevated with a thin, even layer of fat, and the underlying frontalis and excess subcutaneous tissue removed under direct vision. The exposed bed is then sculpted, delayed cartilage grafts are fixed to shape the tip and to brace the alar rim, and a folded lining is separated from the cover so that cartilage can be placed between them. The thinned skin is returned with quilting sutures to define the alar groove. Perfusion on re-inset is noted before the patient leaves theatre.

After a further interval of about a month the pedicle is divided. The proximal stump is trimmed and returned to the medial brow as a small inverted V so that the brows keep their spacing, and the upper margin of the nasal inset is thinned and closed along the subunit border. Division is deferred if any part of the inset has been slow to heal. Where there is doubt, the pedicle can be occluded temporarily and the flap observed before it is cut.

The result is not judged until scars have matured over several months. Review then uses standard photographic views, an assessment of nasal breathing and a patient-reported measure, and compares them with the plan made in Phase 2. Minor revisions, such as defining the alar crease, thinning a nostril margin or opening a narrowed airway, are common in published series and should be presented to the patient from the outset as a possible fourth step and not as a failure.