Mohs Micrographic Surgery Design and Execution of Pedicle Flaps

Anatomy and Physiology

Creating an island pedicle flap severs the epidermal and dermal borders to allow all edges of the pedicle to move freely from one position to another, hence the name "island." A thorough knowledge of the underlying anatomy and facial cosmetic units is imperative to complete the flap without complication and optimize the aesthetics of the closure. Due to the preservation of the subcutaneous vessels, the base of the flap has an increased depth compared to other advancement flaps. 

To optimize the cosmesis of the resulting scar, island flaps should be used in areas where 1 or 2 margins can be hidden in natural contour lines or rhytids.[6] The triangular shape of the flap makes it impossible to camouflage all suture lines into areas of relaxed skin tension. The underlying stalk of the island pedicle flap can vary in length; this length will dictate the scale of flap advancement. Thinning the subcutaneous stalk may enable further advancement but sacrifices the underlying vasculature. Conversely, maintaining a substantial amount of subcutaneous tissue improves vascular supply but decreases flap mobility and may increase wound tension.[6]

Indications

Experienced Mohs and plastic surgeons commonly use the island pedicle advancement flap to close defects to preserve function and optimize cosmesis. The island pedicle flap is similar to other standard advancement flaps in which the primary tension vector is parallel to the direction of the advancing pedicle. Therefore, an indication for using the island pedicle flap includes closing defects in areas where the surgeon needs to preserve a tension vector that remains parallel with the wound. Additionally, the size and location of the defect dictate the utility of the island flap closure.

The island pedicle technique is particularly suitable for several cosmetic units of the face, including the nose, medial canthus, cheek, junction of the upper lip, and even the ear.[7][8][9] These anatomical regions allow the borders of the flap to be camouflaged within the facial rhytids. Additionally, utilizing the island pedicle flap in the brow area allows for the medial advancement of the remaining brow, ensuring facial symmetry and maintaining brow continuity. This technique provides surgeons a valuable option to achieve optimal cosmetic results in these specific facial areas.

Because the island pedicle advancement flap relies on a subcutaneous vascular stalk to preserve the tissue, the flap remains impervious to ischemia.[10] The island pedicle flap technique is particularly beneficial in areas where skin vascularity may be compromised, such as in patients who have undergone prior radiation therapy or individuals with increased operative risk, such as tobacco users.[11]

Technique or Treatment

The island pedicle flap should be designed before making any incisions. The flap should have a tapered tail to allow closure of the secondary defect after advancing the flap into the primary defect. The flap should also include tissue adequate to fill the primary defect, at least 3 times the diameter of the primary lesion. An inadequately sized flap requires more extensive undermining of tissue or the use of a skin graft for defect closure.

Island pedicle flaps can be modified to promote healing and cosmesis. The long legs of the triangular island pedicle can be modified to match the curvilinear lines of the face instead of keeping the borders of the flap strictly linear.[6] Additionally, rounding off the base of the triangle promotes advancing a semicircular flap edge into a semicircular primary defect.

When incising the island pedicle flap, use strict vertical to outward beveled incisions to free the underlying vascular stalk from adjacent subcutaneous tissue and muscle. To advance the island pedicle, undermine just above the superficial fascia around the peripheral edges of the flap and the primary defect; the inadequate undermining of tissue limits the mobility of the flap.[12] To avoid restriction while advancing the island pedicle, the distal or tapering end of the flap must be free from any deep or lateral restraint. The adequate undermining of tissue allows the island pedicle flap to be freely advanced anywhere from a few millimeters to several centimeters depending on the length of the underlying vascular stalk. Failure to free the flap from tension could result in secondary motion of the tissue around the insertion point of the flap. Depending on the anatomical location, placing undue tension on free margins such as the eyelid or lip is highly likely to result in ectropion or eclabium as post-operative wound contraction ensues.[12]

Once the flap is adequately mobile, the first key suture of the repair may be placed in the central portion of the advancing pedicle and into the corresponding point of the primary defect. Following the key stitch, dermal and epidermal sutures may be placed to close first the primary and then the secondary defects.

Complications

The highly vascular stalk of the island pedicle flap resists ischemia but is also the reason for suboptimal cosmetic outcomes. The resulting scar will likely have a raised kite-shaped appearance from epidermal, dermal, and subcutaneous tissue advancing into a defect. The raised appearance of the scar is known as a “trapdoor” or “pincushion” deformity.[13][14] Creation of an island pedicle slightly smaller, 1 to 2 mm per side, than the closed defect mitigates the risk of creating this deformity. This equitably places tension on all sides of the island pedicle flap, reducing the likelihood of postoperative wound contraction. If the trapdoor effect occurs, massage and intralesional steroid injections have been used successfully to reduce the raised appearance of the tissue.

Additionally, as for all advancement flaps, consideration must be given to the type of tissue at the primary defect and the type of tissue being advanced. For example, advancing a hair-bearing area such as the cheek onto a non–hair-bearing site like the lateral nasal sidewall would be disfiguring for a patient.

Clinical Significance

The island pedicle advancement flap offers the advantage of a mobile, centrally located vascular stalk. This characteristic reduces the requirement for extensive undermining compared to other flaps, making it a prudent choice for individuals with bleeding diatheses or those who are taking anticoagulants.[15] The island pedicle flap is a versatile advancement flap that can be employed in various facial regions. Its applicability extends to areas with diminished or compromised vascularity.

Enhancing Healthcare Team Outcomes

A successful island pedicle advancement flap can have ideal cosmetic results and low patient morbidity. The involvement of an interdisciplinary team plays a crucial role in attaining these desired results. For example, after creating a primary defect where an island pedicle flap would be indicated for closure, an experienced plastic or Mohs surgeon may feel comfortable closing the defect themselves. However, in large or cosmetically sensitive defects, some surgeons may not feel adequately trained to close a defect in a way that would cause an area to function optimally or be aesthetically pleasing. In such scenarios, a prudent surgeon will seek the expertise of another surgeon to assist in the closure. Each surgeon knowing their limitations is vital to the safety of their patients and the overall outcomes of surgeries performed. For these reasons, access to a network of physicians to rely on for help is invaluable.

Ancillary staff is also essential in helping patients increase their chance of an optimal cosmetic outcome. Patients may be more able to care for their postoperative wounds when nurses and medical assistants are involved.[16] In the immediate postoperative period, the supporting staff has the undivided attention of the patient to explain wound care instructions and possible adverse events such as bleeding, wound infection, and dehiscence. In doing so, patients may feel more equipped to handle postoperative complications such as bleeding.

Although closing a defect with an island pedicle advancement flap depends almost entirely on the skills of an experienced surgeon, the time and effort provided by the physician, supporting staff, and the individualized nature of the patient's condition are all necessary for a successful overall outcome. [Level 5]