The anterior rectus sheath is one of the firm lateral abdominal aponeuroses of the abdominal external oblique muscle. The efficiency of the sheath in reconstructive surgery has been demonstrated in the repair of full-thickness right ventricular defects after mediastinitis or sternal dehiscence [30], in the treatment of bronchopleural fistulas complicated by empyema [31], in pleural reconstruction of the chest wall [32], dural reconstruction [33], and breast reconstruction after subcutaneous mastectomy [34]. We have utilized this sheath in oromandibular reconstruction with the vascularized free rectus abdominis musculocutaneous flap (RAM). The RAM is effective in the maintenance of the formed bulge of the oral floor, prevention of the sinking of the reconstructed tongue, and prevention of the exposure of reconstruction plates after the resection of the mandibular continuity. Therefore, we consider that RAMs are absolutely indicated for these types of reconstruction (Table 9.2). As is important, the muscle attached to the rectus sheath is harvested with a 3- to 4-cm extension superiorly and inferiorly (Fig. 9.9). Extensive resection of the anterior rectus sheath caused no problems.

In the preparatory phase of swallowing, the tongue margin and the oral floor elevate, retaining the alimentary bolus in the oral cavity with glossopalatal closing function [35] (Fig. 9.10). In reconstructive flaps, however, this function is impaired: the bolus on the reconstructed oral floor cannot be moved to the dorsum of the tongue. When the oral floor is reconstructed with a thin flap, as with a forearm flap to reform it to the pre-resection state, a wide depression results, where saliva and food residues become awkwardly trapped. This makes smooth food transfer difficult, causing a time lag between glossopalatal closure and bolus transfer, as well as mistimed swallowing as a whole resulting in misswallowing [36]. For an efficient swallowing function, it is essential to raise the oral floor to a height similar to that of the tongue margin, thereby forming the preparatory phase of swallowing statically. In other words, the nonfunctioning oral floor should not be depressed. Even when the bulge of the floor is formed with thick and bulky reconstructive materials, like the musculocutaneous flap, the cutaneous and muscular portion, in time, generally sags because of gravity, resulting in the depression of the oral floor. Therefore, we developed a method of forming the mylohyoid muscle-like tissue by fixing the anterior rectus sheath anteriorly and posteriorly to the mandibular areas in a hammock pattern. This protects the muscle from the influence of gravity, allowing the maintenance of the bulge and preventing the sinking of the reconstructed oral floor and tongue. We have termed this method the hammock technique, where a musculocutaneous flap with a firm anterior sheath is indispensable and where RAM is the optimal material. Although the mylohyoid muscle attaches to the hyoid bone, and elevates the oral floor and hyoid bone, in reconstructive surgery, the anterior sheath is not fixed at the hyoid bone because recovering the function by elevating the reconstructed oral floor is not possible even if such fixation is done. Conversely, fixation to the hyoid bone results in flap pulling and, consequently, in hindering the formation of the bulge of the reconstructed oral floor and the raising of the reconstructed tongue by the money-pouch-like reconstruction [37] (Figs. 9.11 and 9.12)

After total resection of the mobile tongue or more extensive resection, it is essential for the purpose of generating swallowing pressure to build the reconstructed tongue with height and roundness, to make the oropharyngeal space narrow, to provide the glossopalatal closing function, to maintain the mobility of the tongue base, and to avoid forming a gap to the posterior pharyngeal wall (Fig. 9.10). To achieve this outcome, the following techniques are essential: (1) the hammock technique (the bulge of the reconstructed oral floor is maintained, and the depression of the reconstructed tongue is prevented), (2) the money-pouch-like reconstruction method [37] (the tongue is reconstructed to give it height and roundness), (3) neuroanastomosis [35] [38] (the reinnervated muscle is used to maintain the bulk of the muscular portion of the RAM), (4) cricopharyngeal myotomy, and (5) resection of the infrahyoid muscles and thyroid cartilage/hyoid bone/mandible fixation. With these serial reconstruction procedures, the anatomical and functional structures of swallowing from the preparatory phase to the pharyngeal phase are statically reconstructed. Therefore, the residual tissues easily assist in the swallowing function.

In reconstruction after the resection of the mandibular continuity with oral defects, vascularized free osteocutaneous flaps are usually the first choice. When bone reconstruction is not possible because of insufficient conditions, however, mandibular continuity is restored with a reconstruction plate. The muscular portion and the anterior sheath are wrapped around the plate, whereby the anterior rectus sheath firmly reinforces the muscular portion. The flap margin is deepithelialized and submucosally inserted into the oral cavity; consequently the sheath on the muscular portion is further reinforced by the dermis. We term this method the wrap-around technique for mandibular reconstruction. To date, plate exposure has not been observed in any of the patients who underwent the procedures of this technique with the anterior rectus sheath (Fig. 9.13). After primary reconstructive surgery, usually 6 months thereafter, secondary generative mandibular reconstruction was carried out by implanting titanium mesh and particulate cancellous bone and marrow (PCBM) in the mandibular defect. A 3D model was prepared from CT images, and the mandibular morphology on the healthy side was reproduced in the defective side using the titanium mesh as a scaffold. PCBM collected from the posterior iliac crest was then buried in the rectus abdominis muscle. New bone formation was usually confirmed 3 months after the surgery, and regenerative mandibular reconstruction was completed in the next 6 months (Fig. 9.14).

Alternative to the muscle sheath alone, the tensor fascia lata flap may also serve as material for these reconstructions [39]; however, RAM appears to be the most efficacious in terms of the facility of flap elevation, the wide caliber and long length of the pedicle, the flexibility of the cutaneous portion (especially, the application to three-dimensional reconstruction), and the maintenance of the bulk of the muscular portion by reinnervation.

Although free tissue transfer is the preferred reconstruction option in most major oral and maxillofacial reconstructions, the pectoralis major musculocutaneous (PMMC) flap is commonly used in the salvage of necrotic free flaps and is the first choice for patients who are not candidates for free flaps. The PMMC flap has a high incidence of distal skin necrosis, however, because of vascular insufficiency resulting in partial to total flap loss and fistula formation [40]. The pectoral branch of the thoracoacromial artery is the main blood supply to the skin island overlaying the upper part of the pectoralis major muscle. The lateral thoracic artery and the anterior intercostals branches of the internal mammary artery supply the skin region overlaying the lower part of the pectoralis major muscle [41–43]. The skin island must be designed in the lower chest to attain a pedicle length sufficient for oral and maxillofacial reconstruction. In the conventional harvesting method for oral and maxillofacial reconstruction, the lateral thoracic artery and all intercostal branches from the internal mammary vessel are cut to avoid compromise of arc of rotation of the flap. The dissections of these two dominant sources of blood supply to the skin island overlaying the lower PMMC flap poses a high risk of distal flap necrosis. The PMMC flap preserves the lateral thoracic vessels in addition to the pectoral branches of the thoracoacromial artery and is, therefore, a very valid choice from the viewpoint of blood supply [41, 44] (Fig. 9.15). Cadaver dissection has also shown that the lateral thoracic artery is a more dominant pedicle of the PMMC flap than the pectoral branch of the thoracoacromial artery in approximately 6 % of all cases studied. This percentage was very close to the total rate of skin necrosis of PMMC flaps [45]. Dissecting the lateral thoracic artery as a routine harvesting technique in such cases could result in total loss of the pectoralis major skin flap.

A skin island designed in the lower chest to reach the oral and maxillofacial defect includes the fourth intercostal perforating branches [43]. The muscle is elevated from the chest wall inferiorly to superiorly. The pectoral branch of the thoracoacromial artery is included in the flap as in the conventional harvesting method of the PMMC flap. The lateral thoracic artery, identified underneath the lateral border of the pectoralis muscle in the region of the maxilla, comes out underneath the lateral border of the pectoralis minor muscle and enters the lateral part of the pectoralis major muscle [46]. The pectoralis minor muscle overlying the lateral thoracic artery is dissected completely to release the lateral thoracic artery up to the clavicle [42]. The lateral thoracic vessels are kept pedicled, not cut, if the length of the pedicle is not compromised. This is called “double pedicled pectoralis major musculocutaneous flap” or “DOP-PMMC flap.” Lateral thoracic vessels should be preserved with the pedicle, not dissected, when the length of the pedicle is not compromised in oral and maxillofacial reconstruction; the flap could reach the oral cavity without limitation, when the pectoralis minor muscle is completely dissected. Compromise of pedicle length is often experienced, especially when wrapping the muscle of the PMMC flap around the titanium reconstruction plate used in segmental mandibulectomy (wrap-around procedure), even when the pectoralis minor muscle is completely dissected. The compromise may be due to the long distance between the thoracoacromial artery and the lateral thoracic at the bifurcation of the subclavian artery, to the short length of the lateral thoracic artery from the bifurcation of the subclavian artery to the point of entry into the pectoralis major muscle, or to the constitution of the patient—a long neck compared with the chest. In such cases, the lateral thoracic vessels are cut at the bifurcation of subclavian vessels, and then microvascular anastomosis is carried out between lateral thoracic vessels and the transverse cervical artery and external jugular vein. We named our new procedure “supercharged pectoralis major musculocutaneous flap (SUP-PMMC flap).” Thus, the lateral thoracic artery is preserved without any compromise of pedicle length, which takes into consideration the blood supply of the lower part of PMMC flaps. Lateral thoracic vessels are suitable for microvascular anastomosis as described for the free lateral thoracic flap and for the lateral thoracic perforator flap [47, 48]. It should be noted that a deficit of the lateral thoracic artery has been reported in approximately 15 % of cases [47, 49]. Although we have not been able to fully resolve the issue of compromised distal skin blood supply because of the necessity of dissecting the branches of the internal mammary artery, it is worthwhile to preserve the lateral thoracic vessel that is the major contribution to the lateral and distal PMMC flap (Fig. 9.16).

The application of a cervical skin flap to oral and cervical defects, subject of many reports, was initially described as “the apron flap” by Ward et al. in 1950 [50]. In 1969, Farr et al. [51] have described a similar flap as a cervical island skin flap. In both studies, blood circulation is described as being of a random pattern. In 1978, Futrell et al. [52] have described an axial-pattern flap by using the submental branch of the facial artery, the dominant pedicle of the platysma, for feeding the platysma musculocutaneous flap and have used it in oral reconstruction. Although the platysma flap and cervical island flaps are very similar, their circulation systems are totally different and should be clearly differentiated, yet they are still being confused in many studies [53]. By taking the circulation systems into consideration, a platysma flap can be elevated safely.

Since the platysma flap is of an axial pattern that uses the submental branch of the facial artery as the dominant pedicle, the skin flap is a complete island. The suprasternal branch of the suprascapular artery and the platysma branch of the suprathyroid artery are minor pedicles; therefore, their circulation system is Mathes’s type II [54, 55]. When a skin flap is used for oral reconstruction, cutting the minor pedicle is requisite, and the skin flap is fed only by the dominant pedicle present in the upper region. Thus, the arc of rotation is determined by this artery (Fig. 9.17). The anterior region in neck skin receives blood supply from the submental branch of the facial artery, with the anterior margin of the sternocleidomastoid muscle regarded as the boundary [56]. Accordingly, a skin island of the platysma flap should be set in this region or in a region from where subcutaneous (dermal) blood flow is foreseen (Fig. 9.18). The submental branch of the facial artery and its arborization are distributed in the deep adipofascial layer and extend perforators to the platysma and skin. Thus, no axial-pattern circulation is obtainable unless this layer is conserved. Imanishi et al. [57] have shown that the dominant pedicle extends a long branch to the deep adipofascial layer and forms a vascular plexus, but it extends only a small vessel to the platysma, and no vascular plexus is formed between the platysma and skin. Thus, elevating a platysma flap as a musculocutaneous flap is risky; it should be elevated as an adipofasciomusculocutaneous flap. This anatomical fact is very important when elevating a platysma flap (Fig. 9.19). Venous circulation in the platysma flap is retrogradely drained by including the external jugular vein [56]. The deep adipofascial layer into which the jugular vein distributes is important for venous circulation. Skin loss has been reported in 20–70 % of platysma flaps [58], but has occurred in only 3 % with the use of our method of elevation. From the viewpoint of cervical lymph flow based on Harnsberger’s fascia classification [59], a platysma flap destroys the structure of the cervical fascia. Moreover, since the deep adipofascial layer is present in the superficial space [59], the platysma flap includes the superficial cervical lymph node. Taken together, these conditions may induce a late neck lymph node metastasis-like abnormality. Nonetheless, we have not encountered any late metastatic case assumed to have induced an abnormality in cervical lymph flow (Fig. 9.20).