Small- or partial-thickness defects of the floor of mouth can be skin grafted or repaired with a facial artery musculomucosal (FAMM) flap. The FAMM flap is based on the facial artery and includes a portion of the buccinator muscle in addition to the buccal mucosa and is usually useful for small defects (2 to 3 cm) that enable primary closure of the donor site.1 This vascularized flap is useful for the coverage of exposed bone and to prevent tethering of the tongue that may occur as a result of graft contracture.

The pedicled pectoralis major myocutaneous (PMMC) flap or pectoralis major muscle flap covered by a skin graft can be also used for extensive floor of mouth as well as many other oral cavity reconstructions. These flaps are based on the thoracoacromial artery and can reliably reach as high as soft palate. The skin paddle of the PMMC flap is reliable when designed to include adequate cutaneous perforators.2 Limitations of the pedicled pectoralis major flap include limited reach, neck contracture due to fibrosis of the proximal muscle, and the potential for an unsightly bulge in the neck. Despite these drawbacks, the PMMC and pectoralis muscle flaps are still frequently used in patients who are poor free flap candidates, as an additional flap in conjunction with a free flap to reconstruct massive defects, or as a secondary option in the event of a free flap failure. Anatomic studies suggest that a PMMC flap skin paddle centered over the 4th intercostal space is optimal in terms of reliability and reach.

Free flaps are the preferred method of reconstruction of floor of mouth defects in patients who have acceptable medical/ surgical risk factors. In these cases, free flaps typically have a more robust blood supply and a better arc of rotation than pedicled flaps. In addition, free flaps can be harvested from a variety of areas enabling the surgeon to transfer tissues that more closely resemble the resected structures. For example, the radial forearm fasciocutaneous (RFF) free flap is useful for moderate to large floor of mouth defects since it is thin and pliable, thus preventing compromised speech or swallowing due to excess bulk or tethering of the tongue. The RFF is based on the radial artery and is rapidly harvested with a long pedicle, thereby facilitating head and neck reconstruction. Drawbacks of the RFF flap are decreased circulation to the hand, risk of tendon exposure due to incomplete skin graft take, radial nerve injury, and an unfavorable donor site appearance in some patients. A suprafascial harvest, in which the fascia investing the forearm muscles and tendons is spared, may decrease donor site morbidity without compromising flap viability.3

For floor of mouth resections that result in substantial submandibular dead space, slightly bulkier flaps, such as the anterolateral thigh (ALT) free flap, are useful. The ALT free flap is based on skin perforators arising from the descending branch of the lateral circumflex femoral artery and vein and is particularly useful in head and neck reconstruction because
it can be transferred either as a fasciocutaneous flap or as a myocutaneous flap depending on the reconstructive needs. When harvested as a fasciocutaneous free flap, it is usually intermediate in thickness between the RFF flap and the vertical rectus abdominis myocutaneous (VRAM) flap. The VRAM flap is based on the deep inferior epigastric vessels and is too bulky in most patients with isolated floor of mouth defects. Although the bulk of the VRAM can be decreased by harvesting it as a fasciocutaneous flap based on the deep inferior epigastric perforatoring (DIEP) vessels, even without the rectus abdominis muscle the DIEP flap is often thicker than the ALT free flap.

The goal of reconstruction for defects involving the buccal mucosa is to prevent cicatricial trismus. Primary closure can be used for small defects, and split- or full-thickness grafts can be used for moderate ones. For defects involving the majority of the buccal mucosa, a thin, pliable fasciocutaneous free flap such as the RFF flap is indicated to prevent scar contracture from limiting mouth opening. The ALT flap may also be used in thin patients and may have the advantage of decreased donor site morbidity as compared with the RFF. Alternatively, the ALT free flap can be thinned considerably at the time of surgery, taking care not to injure the perforator blood supply and the subdermal vascular plexus of the flap, or can be reduced secondarily. Buccal mucosa resections that result in through-and-through cheek defects often require reconstruction with flaps that can either be folded on themselves, de-epithelializing a portion of the flap to allow wound closure at the flap margin, or allow harvest with dual skin paddles. ALT and VRAM free flaps, and less commonly the RFF, can be designed with more than one skin paddle, allowing separate reconstruction of the buccal mucosa and external cheek skin with a single flap.

Partial tongue defects can be closed primarily or with full-thickness skin grafts to prevent graft contracture. If primary closure or a graft is likely to result in significant tongue tethering or an inability to effectively obliterate the oral cavity space due to the size of the defect, a flap is usually indicated for closure. In practical terms, flaps are commonly required for defects approaching half the tongue and larger. Additionally, a through-and-through defect communicating with the dissected neck is usually best addressed with a flap to decrease the risk of fistula. The goal is to allow the residual tongue to contact the premaxilla and palate for speech articulation, as well as to be able to sweep and clear the oral cavity, and move food and secretions from anterior to posterior.4

For hemiglossectomy defects, a thin, pliable flap is needed to preserve tongue mobility, although a small amount of bulk is needed to obliterate the oral cavity dead space with the mouth closed and not create a funnel for secretions to drain directly into the larynx. Here again, most surgeons prefer the RFF free flap oriented such that the distal end of the flap is used to reconstruct the anterior portion of the tongue (Figure 40.1). Adequate flap width is needed to prevent tethering the tip of the tongue to the floor of mouth and to recreate a sulcus. Bulkier free flaps or the PMMC flap can also be used in more extensive resections; however, these options typically have inferior results in terms of speech and swallowing.

The strategy for reconstruction following near-total and total glossectomy is different. In these cases, a bulkier flap is required to reconstruct the greater volume of resection, and flaps such as the VRAM and ALT are commonly used. Swallowing and speech outcomes are better when the flap can be made convex into the oral cavity.5^,6 To do so, it is helpful to design the flap to be somewhat wider than the oral defect, at least 8 to 9 cm in most cases, anticipating some atrophy of the flap with time, particularly if postoperative radiation will be administered (Figure 40.2). Additionally, many surgeons believe that laryngeal suspension using permanent sutures between the hyoid bone and mandible helps prevent prolapse of the flap and improve functional results. If at all possible, concave reconstructions creating a trough-like area should be avoided since pooling of oral secretions is associated with aspiration. In any case, the patient should be counseled preoperatively about the possibility of unintelligible speech, inability to swallow, and chronic aspiration.