Local flap principles

Classification

By blood supply:

• Random flap: nourished by sub-dermal vascular plexus; length-to-width ratio typically 3:1 (less on lower limb).
• Axial flap: nourished by a named artery within the flap (e.g. paramedian forehead flap on supratrochlear vessels). Can be longer and narrower.

By movement:

• Advancement: flap slides directly into defect (V-Y advancement, H-plasty, unilateral / bilateral T-plasty, A-T flap).
• Rotation: pivots around a fixed point (Mustardé cheek rotation, dorsal nasal rotation).
• Transposition: lifted over intact skin into defect (rhomboid Limberg, bilobed, banner).
• Interpolated: pedicle bridges intact skin — divided at second stage (paramedian forehead, melolabial, post-auricular).

Flap planning

1. Define defect by size, site, depth, aesthetic subunit involvement.
2. Identify direction of maximum skin laxity (pinch test).
3. Plan incisions along aesthetic-unit boundaries and RSTL where possible.
4. Protect critical landmarks: free margins (eyelid, lip, alar rim, ear), brow, hairline.
5. Estimate flap tension; donor-site closure as important as recipient.
6. Reverse-plan: ask whether donor defect itself can be closed.
7. Consider future surveillance — Mohs / oncology need to inspect for recurrence; large flaps obscure the original site.

Vascular biomechanics

• Subdermal plexus is dominant for random flaps; preserve fat-and-deep-dermis continuity.
• Length-to-width ratio guides random-flap survival but is anatomy- and site-dependent.
• Smokers, diabetics, peripheral vascular disease and prior radiotherapy reduce safe flap length.
• Indocyanine-green angiography (ICG) increasingly used intra-operatively for marginal flaps.

Execution principles

• Undermine widely in the appropriate plane (sub-dermal for face, sub-galeal for scalp).
• Use atraumatic technique on flap edge; skin hooks over toothed forceps.
• Achieve haemostasis without damaging sub-dermal plexus.
• Inset under minimal tension; place deep support where needed to take tension off the skin edge.
• Trim Burow's triangles where dog-ears form.
• Avoid over-correction at the leading edge — many secondary procedures arise from pin-cushioning or trapdoor deformity.

Practical points

• Match aesthetic subunits: cheek-to-cheek; nose-to-nose. Skin from neighbouring subunits often looks "patched".
• Avoid distortion of mobile structures — eyelid, brow, lip vermilion, ear helix, nostril.
• Plan for two-stage repair early — interpolated flaps (paramedian forehead, melolabial) almost always need pedicle division and refinement.
• Counsel patients on the trade-off between immediate closure and oncological surveillance — flap-covered recurrence can be missed clinically; ensure long-term follow-up plan.
• Photograph pre-operatively, intra-operatively (defect, design), and at follow-up to support audit and CPD.