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  • Understanding flap dynamics is a prerequisite for the performance of any flap procedures.

  • Pivotal, deep, and horizontal restraints all have an important impact on flap design and execution.

  • Accounting for fundamental tissue principles and flap dynamics prior to flap execution permits more successful and cosmetically appealing reconstructive outcomes.

image Beginner Tips

  • Understanding flap dynamics is predicated on an appreciation of the forces that oppose tissue movement.

  • Undermining mitigates most deep restraint, while horizontal restraint is addressed by using a sufficiently lengthy incision that recruits lax skin.

image Expert Tips

  • Horizontal, deep, and pivotal restraints must all be addressed for optimal flap outcomes.

  • Obstructive restraint can be addressed prior to flap movement.

  • On the face, the robust blood supply means that even random pattern flaps may behave more like axial flaps in terms of viability.

image Don’t Forget!

  • Undermining beyond 1 to 2 cm from the incision line may be counterproductive and lead to an increased risk of tissue ischemia.

  • Flap length:width ratios should ideally not be significantly greater than 3:1, at least when working in poorly perfused areas such as the legs. On the face, where most dermatologic surgery flaps are performed, there is often a forgiving and robust blood supply.

image Pitfalls and Cautions

  • Failing to account for pivotal restraint is one of the most common flap design challenges. Appropriately oversizing rotation flaps and widely undermining the pivot point may go a long way to mitigating this problem.

  • Once relocated to the primary defect, flaps should be under minimal tension.

image Patient Education Points

  • Patients should be warned prior to flap closure that they will have an incision stretching well beyond the initially visible defect.

  • Explaining that the additional scar length will likely heal with a minimally visible line may go a long way toward patient reassurance.

image Billing Pearls

  • Flap repair codes (140XX series) include the excision component, so it is not appropriate to bill both an excision and a flap repair code simultaneously.

  • Mohs codes may be submitted along with flap repair codes, though they may be subject to the multiple procedure reduction rule.

  • When coding a flap, medical necessity is the ultimate arbiter of appropriateness.


Flap dynamics are the principles that underpin the movement and behavior of all flaps. By definition, a cutaneous flap is a reconstructive technique that is composed of skin and subcutaneous tissue as well as accompanying vascular supply, which is moved from a donor site to a recipient site. The recipient site is termed the primary defect and, in the context of dermatologic surgery, usually results from the excision of a cutaneous neoplasm. Movement of the flap into the primary defect may create a secondary defect that must also be repaired.


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