Tools
Mohs Micrographic Surgery Design and Execution of Advancement Flaps
Introduction
Surgery of the head and neck results in seemingly countless defects that often require complex closures due to the limited amount of skin laxity or redundancy in these areas. Surgical flaps can facilitate the repair of defects that cannot be closed linearly due to suboptimal function or cosmesis.[1] Advancement flaps offer various closure methods for large defects in a safe, effective, reproducible, and often straightforward way.[2]
While there are many subtypes of the advancement flap, there is often an uncomplicated, unidirectional movement of the leading edge of the flap over the defect being repaired. After the leading edge is sutured into place, tissue redundancy manifests along the margins of the flap. These redundancies can be excised, or the rule of halves allows for suture placement so that the redundancies will be equally dispersed along the length of the suture lines.[3]
The advancement flap differs from other closures, such as rotation or transposition flaps, because the tension vector of the advancing flap remains parallel to the primary motion of the flap.[4] This limits the ability for wound tension to be redirected to a favorable axis. Caution must be exercised when considering an advancement flap in areas where anatomical distortion is undesirable, as the insertion point of the advancement flap will always have some degree of secondary motion.
Once in place, advancement flaps are initially sustained by dermal and subdermal vascular plexuses. As the flap incorporates into the surrounding tissue, neovascularization provides a permanent arterial supply. Through neovascularization, a new arterial supply will support the flap permanently.
Before selecting a flap technique, it is crucial to have confidence that the chosen flap will yield optimal functional results for the patient and achieve the desired cosmetic outcome.[5][6]
Anatomy and Physiology
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Anatomy and Physiology
A complex network of arteries, veins, and lymphatic vessels in the head and neck requires extensive knowledge of the anatomy and vasculature of the face when designing and executing any surgical flap technique, be it an advancement, transposition, or rotational flap. Surgical flaps are classified according to the primary mechanism of their vascular supply and are either arterial or random cutaneous pattern flaps. Advancement flaps are random pattern cutaneous flaps sustained by dermal and subdermal vascular plexuses rather than a large named artery of the head or neck.[4]
The immediate vascular supply to an advancement flap is derived from dense, interconnected dermal and subdermal vascular plexuses. The distal perfusion pressure of this vascular supply determines the initial viability of the flap.[7] Neovascularization occurs as the flap matures and is integrated into the surrounding tissue. Cytokines involved in wound healing release angiogenic factors to induce the formation of vessels that will lead to the long-term survival of the flap. Neovascularization is typically completed within 3 to 7 days after flap placement.[8][9]
Indications
Decisions surrounding the optimal method of primary defect closures require consideration of multiple factors, including the size of the primary and secondary defects, the cosmetic unit affected by the defect, and the availability of redundant skin adjacent to the primary defect. Primary defects that neighbor or are contiguous with free margins, such as the eyelid, naris, or vermillion border, may often require an advanced closure technique such as an advancement flap. In such circumstances, a linear closure technique may span more than one cosmetic unit and result in suboptimal cosmesis.[4][10][11]
Advancement flaps offer the additional benefit of preserving a tension vector parallel to their primary motion, as opposed to linear closures, where the tension vector is perpendicular to the closure line. Advancement flaps typically donate tissue from an area of excess to one of need, offering a relatively low final tension point.
Contraindications
The advancement flap is a safe surgical technique that offers many benefits while having limited contraindications.
A suboptimal functional or cosmetic outcome should prevent using an advancement flap to repair a primary defect.[12] However, some patients may be uncomfortable with the complex postoperative wound care associated with the advancement flap technique and prefer a smaller yet more distorted wound. Informed consent and shared decision-making practices facilitate determining what the patient values most.
Patients taking anticoagulants can still receive Mohs surgery and repair without significant adverse events. However, the amount of tissue undermining required by the advancement flap technique warrants a discussion of the bleeding risks and alternate options for repairing the primary defect.[13]
Technique or Treatment
The most straightforward variation of an advancement flap is the unilateral advancement flap. Creating a unilateral advancement flap requires two parallel incisions, one on each side of the primary defect. These incisions should extend in the direction of the greatest tissue laxity. It was previously believed that proper flap design should incorporate a length-to-width ratio of 3:1; current clinical practice patterns indicate that flaps rarely need to be this long. It is more important to design a flap that is neither excessively long nor results in significant tissue tension.[14] The complete undermining of the advancing tissue allows the flap to advance unrestricted, reducing the amount of secondary movement of the surrounding tissues.
The primary defect and the advancement flap should be designed in a complementary fashion with either rounded or squared edges. Suturing the leading edge of the flap into its corresponding position in the primary defect will create tissue redundancies that can be excised or sewn out using the rule of halves. Redundancies can be excised along the edges of the flap or at its base as dictated by aesthetics. Sewing out redundancies disperses the redundant tissue along the length of each flap edge. Care must be taken during the repair of the primary and secondary defects to minimize the number of sutures and tissue tension. Excessive suturing and tissue tension increase the risk of distal flap ischemia and may result in flap failure.
Complications
Bleeding, infection, and scarring are complications of any procedure that compromises the skin, and advancement flaps are no exception. Advancement flaps can be used to close significant defects, and intraoperative bleeding is the most clinically relevant complication of advancement flaps and the most common complication posed by Mohs micrographic surgery.[13]
Minimization of bleeding risk begins in the preoperative period through medication review and reconciliation, including over-the-counter medications. Patients taking anticoagulants should be counseled to continue their current regimen, as the risk of a thrombotic event outweighs the perceived risk of intraoperative bleeding.[15]
Blood pressure and generalized anxiety management in the preoperative period also reduce the risk of intraoperative bleeding. Using local anesthetics with vasoconstrictors such as epinephrine may reduce intraoperative blood loss.
If postoperative bleeding is anticipated, placing a drain at the flap base can decrease the risk of hematoma formation, which can compromise the viability of the advancement flap.
Clinical Significance
The appropriate use criteria for Mohs micrographic surgery limits applying this procedural technique to sites with limited tissue redundancy or laxity, such as the lips, nose, cheek, and forehead.[16] The linear repair of a primary defect in these anatomical areas may be implausible due to severe distortion of the surrounding structures.[17][18] The advancement flap technique provides an invaluable alternate closure option to improve functional and cosmetic outcomes for patients undergoing Mohs micrographic surgery.
Enhancing Healthcare Team Outcomes
Advancement flaps are commonly used when there is a large defect on the head and neck that cannot be closed linearly due to the adjacent area lacking excess tissue. Defects that begin on the cheek can quickly involve areas such as the eyelid, nose, ear, or lips. As a Mohs surgeon excises tissue from such areas, they must know their limitations regarding their abilities to close a particular defect.[19][2] Depending on the defect, the repair may involve anatomical structures better suited for repair by another specialty. In these circumstances, maintaining an interdisciplinary approach to patient healthcare is invaluable.
Although many dermatologists and Mohs surgeons practice in an outpatient setting, maintaining an interdisciplinary network of physicians of varying skills and abilities to care for a patient in the safest and most effective manner remains paramount.[20] (Level 5)
References
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