Background
An interpolation flap is a 2-stage tissue flap in which the base of the flap is not immediately adjacent to the recipient site. These flaps are used when insufficient tissue or mobility in nearby skin prevents coverage of a surgical defect with primary closure or an adjacent flap. Interpolation flaps are similar to transposition flaps in that the flap is lifted over an area of normal skin to reach the defect. While the base of a transposition flap is adjacent to the defect, the base of the interpolation flap is located a distance away from the area to be repaired. This arrangement results in a bridge of tissue, or pedicle, between the flap base and the surgical defect that typically must be removed in a second stage after vascularity is established between the wound and the flap. [1]
The following 3 interpolation flaps are used most commonly in dermatologic surgery:
-
Forehead flap
-
Cheek interpolation flap
-
Postauricular flap
The forehead flap uses tissue from the forehead to repair the nose. [2] The cheek interpolation flap takes advantage of the loose skin of the cheek to repair small but somewhat deep defects in the nose, and the postauricular flap uses skin from the posterior part of the ear and the retroauricular aspect of the scalp to repair defects in the helix and anterior surface of the ear.
Also see Forehead Anatomy, Forehead and Temple Reconstruction, and Cheek Reconstruction.
History of the Procedure
The forehead flap is believed to have been used in India as early as 700 BCE. Antonio Bronca of Italy performed the procedure in the 15th century. The first reports of the midline forehead flap in the English-language literature appeared in 1793. Since the 1960s, many advances have been made, including Menick's use of the paramedian forehead flap, which is based on a narrow vascular pedicle supplied by the supratrochlear artery. [3] This modification allows easier closure of the forehead defect, as well as greater flap mobility, and it is currently the most commonly used forehead interpolation flap.
The cheek interpolation flap is believed to have been used since 600 BC, when it was first used in India. In contrast, the 2-stage postauricular helical flap is a relatively recent technique, which Lewin described in 1950. [4]
Indications
The forehead flap is used to repair more extensive defects on the nasal tip and ala for which simpler techniques cannot provide adequate coverage. It is sometimes used to provide nasal lining as well. In very extensive defects, the forehead can be used in combination with other techniques such as microvascular free flaps, cartilage or bone grafts, and mucosal flaps to achieve satisfactory function and appearance. [5, 6]
Select small-to-medium, deeper defects on the nasal ala and nasal tip can be repaired by using the cheek interpolation flap.
The postauricular helical flap provides good coverage and cosmesis in medium-to-large defects on the helix and adjacent antihelix, with or without the loss of small amounts of cartilage. [7]
The described interpolation flaps are most commonly used to repair surgical defects resulting from tumor excision, but they can also be used to repair traumatic wounds.
Relevant Anatomy
The paramedian forehead flap is an axial flap based on the supratrochlear artery. Cadaver studies show that the supratrochlear artery exits the orbit 1.7-2.2 cm from the midline, passing deep to the orbicularis oculi muscle and ascending superficial to the corrugator supercilii muscle. It then passes medial to the eyebrow and through the frontalis muscle ascending superiorly in the subcutaneous tissue, 1.5-2 cm from the midline. The angular and supraorbital arteries also contribute to the vascularity of this flap through a rich periorbital plexus of anastomoses. [8]
The cheek interpolation flap is a random flap, but it receives an ample blood supply from the perforating branches of the angular, nasal, and superior labial arteries.
The postauricular scalp has a rich vascular supply from branches of the posterior auricular, superficial temporal, and occipital arteries. Therefore, the postauricular helical flap, which is a random flap, is rarely affected by vascular necrosis.
Also see Anatomy in Cutaneous Surgery.
Contraindications
The use of pedicle flaps is contraindicated in patients who are unwilling or unable to tolerate multiple-staged surgical procedures. Likewise, these procedures should be avoided in patients who cannot leave their surgical sites undisturbed, or special measures must be taken to protect the sites in these patients.
Actively infected skin should never be covered with a flap or used to form a flap. With a forehead with a low vertical height, a variation of the forehead flap or another repair method may be required.
Smoking is a relative contraindication to the use of staged island pedicle flaps because it increases the risk of flap necrosis. However, procedures with these flaps can usually be performed safely if fat is not thinned from the undersurface of the flap. In addition, avoiding the use of previously radiated skin or a previous surgical site is generally best, unless no better repair options are available.
Interpolation flaps should be performed with great care in patients who are receiving anticoagulant therapy or in patients with bleeding disorders. Consultation with the physician who prescribed the medication is prudent before discontinuing any anticoagulant therapy. The author rarely discontinues warfarin prior skin surgery. Similarly, the author only stops aspirin usage initiated by the patient and not when prescribed by a physician. Contacting consulting physicians is appropriate before operating on individuals with bleeding dyscrasias.
-
Nasal defect after Mohs surgery. The boundaries of the nasal tip are outlined for excision to allow replacement of the entire anatomic subunit.
-
Surgical defect.
-
Diagram shows a nasal defect due to tumor removal and the remnants of significantly involved anatomic subunits.
-
Doppler ultrasonography is used to identify the course of the supratrochlear artery prior to flap surgery.
-
The course of the supratrochlear artery is identified by using Doppler ultrasonography and marked on the skin.
-
Gauze or other flexible material is used to measure the necessary length of the flap, and a mark is made at the most distal portion.
-
The gauze is rotated and placed over the course of the supratrochlear artery, and the distal end of the planned flap is marked on the forehead skin.
-
A foil template of the surgical defect is placed with its most distal aspect touching the mark representing the distal end of the flap. The template is outlined with a surgical marker.
-
Template of nasal tip subunit is drawn on the forehead after the length of tissue flap needed to reach the defect is carefully measured.
-
A 1- to 1.5-cm-wide pedicle is drawn over the course of the supratrochlear artery from its origin to the outline of the template.
-
Planned nasal subunit excision and flap incisions are drawn with a surgical marker.
-
Forehead flap is elevated and ready for placement.
-
Flap affixed to nasal wound with planned closure of forehead donor defect.
-
Paramedian forehead flap in place. Although a full-thickness skin graft was later placed in this patient, the widest portion of the forehead donor site is usually allowed to granulate.
-
The forehead flap is incised, elevated, and sutured into the nasal defect. The forehead defect is repaired as completely as possible, and any remaining defect on the forehead is allowed to heal secondarily.
-
Appearance 2 weeks after flap surgery, immediately after division and inset of the pedicle flap. A delayed full-thickness skin graft has been placed in the donor defect on the forehead.
-
The pedicle is severed in 2-3 weeks, and the flap is inset in the proximal portion of the wound. The proximal stalk can be excised and inset in an inverted V shape, as shown in the diagram.
-
The proximal pedicle can be excised in a fusiform fashion, and the defect can be closed primarily. This is the preferred method in the author's experience.
-
Forehead flap at 3 weeks, at the time of suture removal.
-
Nasal defect prior to cheek interpolation flap repair.
-
Nasal defect.
-
Template of nasal defect. This may be expanded to include entire anatomic subunit.
-
Template is rotated and placed on medial cheek.
-
Nasal defect with planned cheek interpolation flap. The needed flap length was previously measured with a rolled gauze, and a template of the defect is used to mark the necessary width of the flap.
-
Cheek flap sutured in place.
-
Cheek interpolation flap is elevated and trimmed to fit into the nasal defect after the cheek donor defect is closed.
-
Appearance after division and inset of cheek interpolation flap. The proximal pedicle will be excised and the resulting defect will be closed primarily.
-
Appearance of the cheek interpolation flap after division and inset. The proximal stump of the pedicle has been excised as an ellipse, and the cheek defect has been closed primarily.
-
Cheek interpolation flap after division and inset.
-
Postoperative result of cheek interpolation flap before dermabrasion.
-
Alternately, skin can be incised and a subcutaneous pedicle may be used.
-
Subcutaneous pedicle flap in place.
-
Finished repair.
-
Helical rim defect after Mohs surgery.
-
Surgical defect on the helix of the ear.
-
Planned incision for a postauricular flap.
-
Planned postauricular flap is marked on the skin. The flap should be of sufficient size to cover the defect without significant tension in any direction. Burow triangles are planned to allow advancement of the skin.
-
Postauricular flap sutured in place.
-
A postauricular flap is sutured in place. One or 2 temporary retention sutures can be placed between the ear and the postauricular skin to decrease tension, if necessary.
-
Mohs surgery defect anterior to the helix.
-
Postauricular flap in place.
-
Postauricular flap after division and inset.