An interpolated flap is a two-stage technique in which the base of the flap is not directly adjacent to the recipient defect. These flaps are used when insufficient tissue or mobility in nearby skin prevents the coverage of a surgical defect with primary closure or an adjacent flap. The use of an interpolated flap results in a bridge of tissue, or pedicle, between the flap base and the surgical defect. It must be removed in a second stage after establishing vascularity between the wound and the flap.
Examples of interpolated flaps include:
Interpolated flaps are often based on a named vascular supply, but frequently include more random blood supply at the distal edges. The paramedian forehead flap is an axial flap based on the supratrochlear arterial blood supply, although some authors have reported that with the abundant anastomoses in the forehead, it can be performed as a random flap. This flap can also be based on the supraorbital vessels, though this is uncommon. The melolabial (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 interpolation flap is also a random flap with a broad pedicle supplied by branches of the posterior auricular, superficial temporal, and occipital arteries. The deltopectoral flap is an axial flap based on dominant perforators from the first three intercostal vessels, though becomes a random flap if it is elevated past the deltopectoral groove. Waltzing flaps can be either axial or random, depending on the location. In facilities with microsurgical capabilities, these last two flaps are rarely called for.
After the interpolated flap is raised and inset in the first surgery, the bridging pedicle is left in place to allow neo-vascularization between the flap and recipient site. For most paramedian, melolabial, and postauricular flaps this connection is maintained for three weeks, then the pedicle is divided. For deltopectoral flaps and waltzing flaps, four to six weeks is often required before the pedicle can be divided safely.
Interpolated flaps are used when insufficient tissue or mobility in nearby skin or soft tissue prevents the coverage of a surgical defect with primary closure or an adjacent flap. The forehead flap is especially useful on larger defects that are deep or full-thickness and located on the distal nose. Cheek interpolation flaps are useful on the distal third of the nose, especially laterally, in situations in which adjacent tissue transfer or full-thickness grafts are not practical. The postauricular interpolation flap is utilized in medium-to-large defects on the helix and adjacent antihelix, with or without the loss of small amounts of cartilage, in situations in which single-stage flaps are not adequate for coverage. Deltopectoral flaps are used for large wounds of the face, head, or neck where no other options are technically feasible. Waltzing flaps can be used anywhere in the body, though they are historically more common in the head, neck and upper extremities where microsurgical techniques are unavailable. 
The use of interpolated 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 not be covered with a flap or used to form a flap. When performing the paramedian forehead flap (PFF) on a patient with a forehead of low vertical height, a variation of the forehead flap or another repair method may be required to avoid transferring hair-bearing skin to the nose, or the patient must be counseled that subsequent hair removal will be required via laser or electrolysis.
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 excessively 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. Interpolated 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. Contacting consulting physicians is appropriate before operating on individuals with bleeding dyscrasias.
Equipment required for interpolation flaps is generally the same for other local or regional flap surgery, with a few possible additions.
Interpolation flaps can generally be performed with one surgical assistant, primarily to help manage bleeding and cut suture.
We find that it is very helpful to show patients (and their families) illustrations when discussing interpolation flaps prior to surgery. Otherwise, it can be difficult for patients to understand what is about to happen in the surgery and in its aftermath. Serial postoperative photographs can help allay concerns and help patients understand that the final result will take time. It is also essential to explain that minor revisions or "touch-up" procedures may be indicated in the weeks or months after the initial procedure to obtain optimal results.
Forehead Flap (Paramedian Forehead Flap, PFF)
The PFF technique first was used in India as early as 700 BC. For many years, a broad midline flap was popular. In the 1960s Menick introduced the PFF, which had a much more narrow and mobile pedicle based on the supratrochlear artery. The PFF uses tissue from the forehead to repair larger, deeper defects on the distal nose (fig. 1a), and sometimes provide nasal lining. In more extensive defects, the forehead flap can be used in combination with other techniques such as microvascular flaps, cartilage or bone grafts, and mucosal flaps. The PFF is an axial flap based on the supratrochlear artery (fig. 1b). The supratrochlear artery exits the orbit 1.7-2.2 cm from the midline, passing deep to the orbicularis oculi muscle and ascending superficially to the corrugator supercilii muscle. It then passes medial to the eyebrow and through the frontalis muscle ascending superiorly in the subcutaneous tissue and 1.5 to 2 cm from the midline. A similar flap can be based on the supraorbital vessels, but the course of the resultant bridging pedicle typically obscures vision in the ipsilateral eye until it is divided, so this remains an option of last resort.
The distal nasal defect is examined prior to designing the PFF. A template of the final defect is made, and the location and course of the supratrochlear artery can be identified by using Doppler ultrasonography or anatomic landmarks. The supratrochlear artery runs toward the scalp within 3 mm of a line drawn up from the medial canthus. Other authors have demonstrated the safety of simply taking a pedicle from the glabellar midline to 1.2 cm lateral to the midline. If more than 50% of an anatomic subunit is involved in the surgical defect, it is often preferable to remove the remainder of the subunit to obtain a better aesthetic result. A template of the defect is made, and then tubed gauze or another flexible material is used to measure the needed length for the flap to rotate and reach the defect from the pedicle base. The tube gauze is rotated to the forehead and the inverted template pattern is marked at the uppermost aspect of the pedicle. From that area, a 1 to 1.5 cm pedicle is drawn down to the planned pedicle base. The flap is then mobilized with its base situated at the inferior aspect of the forehead and often around the orbital rim (fig.1c). The forehead donor site is closed primarily and if the wider portion of that defect will not close completely, it is preferable to allow it to heal secondarily rather than to apply a skin graft (fig.1d). The flap is then thinned distally and secured in the nasal defect with simple interrupted sutures. At three weeks postoperatively the pedicle trunk is excised, and its base defect is best closed primarily. If there is any question of the viability of the flap at the planned division, the pedicle can be pinched to observe the distal flap tip. If it blanches with occlusion of the pedicle, additional time for neo-vascularization should be allowed prior to division and inset. The incised portion of the nasal flap is then thinned and inset into the defect. Minor revision procedures may be indicated during the coming weeks, and it is best to discuss this with the patient prior to starting this flap.
First used in India in about 600 BC, the medial cheek skin is an excellent color and texture match for defects on the caudal third of the nose (fig. 2a). Based superiorly, the cheek interpolation flap can be based on a cutaneous (fig. 2b) or a subcutaneous pedicle (fig. 2c). The subcutaneous pedicle has greater mobility and vascular supply than the cutaneous pedicle. For small-to-medium alar defects, an inferiorly based flap can also be used to avoid the transfer of facial hair. 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. Small-to-medium, deeper defects on the nasal ala and nasal tip can be repaired by using the cheek interpolation flap. Foil or nonabsorbent surgical dressing is used to make a template of the surgical defect to be repaired. Gauze is rolled into a tube, and one end is held in place in the area of the planned flap base, in and lateral to the melolabial crease. While the proximal end is held in place, the remainder of the gauze tube is turned to overlap the wound without tension. The most distal portion covering the wound is marked, and the gauze is swung back into the melolabial crease to mark where the flap should reach. The template is placed on the cheek with its superior edge placed medially and touching the melolabial crease. The portion of the template representing the lateral wound edge furthest from the flap is placed most inferiorly (or distally) on the cheek, touching the mark previously placed on the cheek. A tapered incision is planned distal to this tissue and parallel to the melolabial crease to allow closure without a dog-ear defect. The flap is mobilized, thinned, trimmed and secured in the recipient wound (fig. 2d). The cheek donor site is sutured and the pedicle is wrapped in non-adherent dressing material. The flap is divided and its remainder is inset in about 3 weeks. The remainder of the donor defect is repaired at that time (fig. 2e).
First described by Lewin in 1950, the postauricular interpolation 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 (fig. 3a). Branches of the posterior auricular, superficial temporal, and occipital arteries supply the broad pedicle of this flap. Although it is a random flap, it is rarely affected by vascular necrosis. This flap uses skin from the posterior ear and retro-auricular sulcus and retro-auricular skin to repair defects of the middle third of the auricular helix and adjacent skin. Scars remain well hidden behind the ear. Reconstruction begins by making a template of the helical defect. The template is placed behind the ear with its leading (anterior) edge over the loose portion of the posterior ear and the planned flap is drawn with a surgical marker (fig. 3b). Lines are drawn toward the scalp, gradually tapering outward as they approach the hairline. Burow's triangles can be drawn lateral to the base of the pedicle, but the actual excision of the triangles is often not necessary. Incisions are made through the skin along the planned lines, and the flap is elevated. The surrounding tissue is undermined for a short distance to allow greater tissue mobility, decrease pincushioning, and allow better placement of subcutaneous sutures. The flap is draped over the defect to ensure that coverage of the anterior portion of the defect does not cause excessive tension, and the Burow's triangles can be excised if necessary. Electrocoagulation is used to obtain meticulous hemostasis before the sutures are placed, making every effort to avoid postoperative bleeding. A few interrupted, subcutaneous, absorbable sutures can be used to securely anchor the flap into place, and superficial sutures are placed for fine approximation (fig. 3c). Particularly on the posterior aspect of the ear, it is preferable to use absorbable sutures to avoid the need to manipulate the ear for suture removal. A few bolster sutures can be placed through the flap into the cartilage to recreate the helical sulcus if desired. Division and inset are performed at about 3 weeks. The postauricular donor defect may be closed or allowed to heal secondarily.
The deltopectoral (DP) flap was first described by Aymard in 1917 and remained a workhorse reconstructive option in the early and mid-20th century. In the era of modern reconstructive surgery, particularly with the widespread availability of microvascular surgery in many centers, this flap is not often used. It is a very valuable technique in centers where microvascular surgery is unavailable. It can recreate massive skin and soft-tissue defects of the head, face, oral cavity, pharynx, neck, and chest. Its blood supply is based on perforators from the first three intercostal spaces. This blood supply is robust and reliable up to the deltopectoral groove. The blood supply is random distal to the deltopectoral groove overlying the deltoid muscle. If a flap of this length is required, it is best to raise the distal tip back to the deltopectoral groove as a first procedure, wait one week for blood supply to mature, then raise the remainder of the DP flap at that time and inset it. The location of the perforators can be identified by palpating the intercostal spaces at the sternum. Doppler can be used if desired but is not necessary. The flap is drawn with tapering borders superiorly and inferiorly towards the acromion, gradually narrowing the width until the desired flap width is achieved. Elevation is performed sharply from distal to proximal, often elevating the fascia of the deltoid and pectoralis major with the flap. Care must be taken not to injure the brachiocephalic veins coursing through the deltopectoral groove. The flap is elevated in this plane up to 2cm from the sternal border to avoid injuring the perforators. The flap is then rotated and inset with 3-0 Vicryl sutures deeply, and appropriate skin or mucosal sutures as warranted for the defect superficially. The donor site can typically only be closed partially, and a skin graft is often required over the deltoid muscle. This can be taken from anywhere convenient, though the thigh and abdomen are common donor sites. The interpolated pedicle is broad, and gently tubing the pedicle with 3-0 Vicryl sutures can minimize oozing. A head-shoulder restraint consisting of adhesive tape used to tilt and secure the head to the ipsilateral shoulder should be work for the first week. The pedicle is divided in six weeks, and the majority of the interpolated pedicle skin can be rotated and replaced into the donor site.
Potential complications common to all skin surgery include infection, scarring, bleeding and disfigurement. In addition, pedicle necrosis is possible but infrequent.
Interpolation flaps provide a method of repairing surgical defects that otherwise would be difficult, if not impossible, to repair with other reconstructive techniques.
The surgical team should pay particular attention to control and prevention of postoperative bleeding, which is most commonly experienced in the first 24-28 hours after surgery. Salient points are outlined below.
The paramedian forehead flap is especially prone to postoperative bleeding, most commonly from the proximal flap pedicle in the glabella/brow area. This is best managed as follows:
Cheek interpolation flaps are not as prone to heavy bleeding, but do tend to ooze in the early postoperative period.
Postauricular transposition flaps, when they bleed, are particularly challenging due to being located in the tight quarters behind the ear, which is draped with a flap. Prevention is key to success.
Deltopectoral flaps and waltzing flaps can bleed from the large, wide exposed pedicles
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