Mohs Micrographic Surgery Design and Execution of Rotation Flaps

Anatomy and Physiology

Designing a rotational, transpositional, or advancement surgical flap requires a thorough understanding of the pertinent anatomy, including involved neuromuscular and vascular structures. Vascular anatomy is particularly important to flap design because it ensures adequate flap perfusion and survival. Surgical flaps are broadly classified as arterial or random pattern cutaneous flaps. Rotational surgical flaps are a subtype of random pattern cutaneous flaps as they predominantly rely on deep and unnamed musculocutaneous arteries for flap perfusion instead of routinely utilizing a specific artery.[3]

Indications

The primary indication for employing rotational surgical flaps is a situation where a linear closure would yield an unsatisfactory aesthetic or functional outcome. Rotational surgical flaps utilize adjacent redundant skin to fill the primary defect to achieve a more optimal result. Additionally, surgeon preference and experience with specific types of surgical flaps may play a role in their selection.

The defining characteristic of rotational flaps is their curvilinear nature, which allows them to pivot into position rather than being advanced linearly.[3] This pivotal movement redirects wound closure tension away from the primary surgical defect and distributes it along the length of the flap. Consequently, triangular-shaped defects are ideal candidates for rotational flaps due to the asymmetrical advancement of one end of the flap over the other.

Rotational flaps have only 2 borders, simplifying the concealment of suture lines within preexisting resting skin tension lines. In contrast, the rhomboid flap has 4 borders that must be sutured. Thus, a rotational flap is more likely to provide an aesthetically favorable outcome with suture lines that are easier to camouflage and integrate with the surrounding tissue.

Rotational flaps may be employed to repair defects in nonfacial areas and defects involving the larger facial cosmetic units such as the cheek, temple, and scalp.[2][4][5] Rotational flaps may also be selectively employed in more sensitive areas such as the nose or eyelid, but these tend to be specialized circumstances best executed by an experienced surgeon. The dorsal nasal rotation flap is a specialized rotation flap that can repair defects on the nasal dorsum measuring up to 2 centimeters in the greatest dimension. When properly employed on select patients, the dorsal nasal rotation flap has consistently and reliably produced satisfactory aesthetic and function outcomes.

Other specialized rotational flaps are the Mustarde and Tenzel flaps used when repairing defects adjacent to the eye.[6] The classic Mustarde flap uses the laxity of the cheek and temple to rotate into a defect involving the lower eyelid. The classic Tenzel flap also repairs defects involving the lower lid but does so by utilizing the tissue from around the orbicularis oculi and temple.

Contraindications

Many areas of the head and neck are unsuitable for a rotational surgical flap repair secondary to the lengthy incision lines required to allow adequate flap movement and reduction of wound tension.

Technique or Treatment

The successful execution of any surgical flap requires skill, expertise, and a comprehensive understanding of flap techniques. Central to the success of the rotational flap technique is positioning the flap in immediate adjacency to the primary defect, facilitating its eventual rotation into the desired position. Accomplishing this involves executing a long curvilinear incision along an arc, a crucial aspect of flap design aimed at minimizing wound closure tension. However, an excessively long arc, where the pedicle's length greatly surpasses the base width, may compromise flap survival due to diminished vascular supply at the distal tip compared to the base.[7]

After the incision, extensive undermining of surrounding tissue is imperative to alleviate movement restrictions. Given the inherent tissue stiffness, rotational flaps invariably retain some residual tension, particularly along their pivot point. Proper flap sizing is crucial to tension reduction; an undersized flap may lead to excessive tension at the distal margin. To mitigate this concern, the flap can be intentionally oversized and extended vertically beyond the defect, thereby reducing pivotal restraint, minimizing tension, and preventing the need for secondary tissue motion around the defect.[7] Cases involving immobile skin regions like the scalp may benefit from a back cut to enhance flap mobility. However, back cuts can interfere with the preexisting vascular supply and increase the risk of flap failure.

Complications

Procedures that compromise the epidermal barrier risk complications such as infection, scarring, and bleeding; bleeding is the most common complication of rotational flap procedures in Mohs micrographic surgery.[8]

Intraoperative and postoperative bleeding can be mitigated using a multifaceted approach. Lidocaine with epinephrine induces vasoconstriction and reduces intraoperative bleeding. Employing electrocautery, electrocoagulation, and electrofulguration decreases bleeding intraoperatively. If postoperative bleeding is expected, pressure dressings or wound drains may be utilized; drains offer the added benefit of preventing hematoma formation that can compromise flap viability. Patients on anticoagulation therapy should not discontinue their regimen to reduce intra- and postoperative bleeding; the risk of a thrombotic event is substantially more important than any perceived risk of bleeding during or after surgery.[9]

Many complications with rotational are rooted in poor flap design. If the arc adjacent to the primary defect is too short, there will be excessive tension on the flap, especially the distal tip. Excessive tension increases the risk of distal ischemia and secondary motion in the surrounding areas, resulting in tissue distortion. Contrarily, if the arc is significantly longer than the flap width, there will be decreased perfusion along the distal tip of the pedicle, which may also lead to ischemia.

Clinical Significance

The appropriate use criteria governing Mohs micrographic surgery confines the scope of practice for Mohs surgeons to anatomical sites characterized by limited tissue redundancy or laxity, including the lips, nose, cheeks, and forehead.[10][4] When tissue redundancy is scarce, effecting a linear defect repair becomes implausible due to the potential for pronounced distortion of the surrounding anatomical structures.[11][12] Advanced flap techniques are of paramount significance when addressing a nonlinear defect repair.

The delineation of appropriate use criteria for Mohs surgery emanated from a collaborative effort in 2012, wherein prominent dermatological organizations, including the American College of Mohs Surgery, converged to establish standardized guidelines.[13] These guidelines encompassed a comprehensive evaluation of factors encompassing tumor type, dimensions, and site, among others, to discern the optimal eligibility of lesions suitable for Mohs micrographic surgery. The selection bias leans towards regions of constrained cutaneous laxity or redundancy, predominantly localized within the facial and cervical domains. Within these anatomical precincts, the viability of effecting linear closures as the preferred mode of defect closure is not universally tenable, thereby underscoring the indispensability of recourse to advanced surgical closure modalities, exemplified by the advancement flap technique.

Enhancing Healthcare Team Outcomes

As a Mohs micrographic surgeon seeks to close large primary defects on the face, keeping an open line of communication with other specialists such as otolaryngologists, plastic surgeons, and ophthalmologists is imperative.[14][15] Due to the nature of Mohs surgery, the lesion can become much more extensive or invasive than initially determined. As a defect becomes larger than what a particular surgeon feels appropriate to manage in an outpatient setting, they can resort to trusted colleagues in adjacent specialties. Even if a particular defect is manageable, the location and surrounding structures may deem it better suited for another specialty, such as the lid margin with ophthalmology or the external auditory canal with otolaryngology. 

In conclusion, although many Mohs surgeons may feel comfortable with large repairs, maintaining an interdisciplinary network of trusted physicians allows for the most effective and safest care for patients.[16]