Mandibular Reconstruction

Since the late nineteenth century, many reconstructive techniques have been used for mandibular restoration after extirpation of oral cavity malignancies or traumatic injury. The challenge of achieving oromandibular rehabilitation is a formidable task involving soft tissue restoration as well as bone in most cases. Ideally, the aim of the reconstruction is to achieve both a functional and aesthetic restoration, addressing specific functions related to the oral cavity, including salivary continence, aspiration, mastication, deglutition, and speech. Prior exposure to irradiation and chemotherapy may further complicate the success of a restoration.

The complex issues related to restoration of the oro-mandibular defect are best highlighted by work done during World War II, when traumatic mandibular injuries were treated with static splints. Patients were often left with severe contractures and, as oral cripples, were unable to maintain oral compe-tency.24 The sequelae related to delayed mandibular reconstruction were observed quite early in history. In an effort to prevent these sequelae, nonvascularized rib, tibia, clavicle, and iliac bone were all used to primarily reconstruct the mandible during the early 1900s.24'25 Progressive resorption and the inability of the bone to withstand the axial stress associated with mastication led to poor results.26 To address this problem, Snyder et al.27 and Conley28 reported on the use of pedicled osteocutaneous flaps for mandibular reconstruction. A decade later, Barnes et al.29 pedicled clavicle on sternocleidomastoid muscle and Biller et al.5 reported on the use of rib pedicled on pec-toralis major muscle. The success rate of these techniques, however, was quite poor, largely because the bone stock and vascular supply were inadequate.30 The introduction of bone plating systems during the mid-1970s seemed to fulfill many of the requirements for successful mandibular reconstruction. Early results reported by Klotch and Prein31 appeared promising; however, complications, including plate extrusion, fistula formation, delayed plate fractures, and poor functional results, limited the success of reconstruction plates.61 The complications associated with reconstruction plates were exacerbated by the use of adjuvant external beam irradiation, which had been used more frequently since the early 1980s. Although other concerns such as radiation scatter associated with the presence of metal plates were poorly defined at this time, the most significant drawback to this system was the inability to achieve lasting functional oral rehabilitation in these patients. Because the insertion of osseointegrated dental implants was not possible with metal plate reconstruction, the retention and stability of functional dentures could not be achieved.32

Free tissue transfer for mandibular reconstruction was first introduced in 1974 by Ostrup and Fredrickson,33 who used revascularized rib in the canine model. Shortly thereafter, McKee34 and Daniel35 applied this technology in humans and, although revascularized rib is no longer used clinically, this pioneering work revolutionized mandibular reconstruction. Composite defects involving the mandible and its adjacent soft tissue could now be reliably reconstructed with vascularized bone as well as adjacent vascular-ized soft tissue, obviating the need for a second soft tissue flap. Using fluorochrome markers, Ariyan36 demonstrated the role of the periosteal blood supply and the ability to safely perform contouring osteotomies. Baker and Sullivan37 demonstrated that transferred bone formed a strong union with the adjacent native mandible after 6 to 8 weeks, even in irradiated patients.

As the advantages of vascularized bone became evident, a number of new donor sites for composite flaps were described. The fibula,38 iliac crest,39 and scapula40 donor sites have become the most popular sources of vascularized bone. Inherent differences in each donor site, with regard to bone stock, soft tissue quality, potential for sensory reinnervation, and pedicle geometry, dictate the best choice for reconstruction. The fibula, iliac, and scapula donor sites all provide bone stock sufficient for dental implants in most patients,41 which Urken et al.42 have demonstrated, is an essential factor for optimal oral rehabilitation. Successful reconstruction of the oral complex requires control of salivary continence, prevention of aspiration, functional mastication, and speech. Vascularized bone flaps permit primary reconstruction of the oromandibular complex, avoiding contractures and scarring which often complicate secondary reconstruction.42,43 Although the recipient bed is often compromised by salivary contamination and prior irradiation, vascularized bone grafts remain capable of healing to the adjacent native mandible such that they may withstand the loading forces associated with mastication.44,45 Furthermore, the soft tissue components harvested with each of these three composite flap donor sites serve as useful sources of tissue for either intraoral lining or extraoral coverage.46

It has become clear that mandibular reconstruction can now be achieved in the primary setting in a safe and reliable manner with minimal donor site morbidity.47,48 It remains a complex challenge, the results ofwhich greatly influence the patient's postoperative quality of life.49 In addition, primary oromandibular reconstruction has had a significant impact on disease management. This procedure has eliminated some of the guesswork for the surgeon in deciding whether a marginal mandibulectomy was a safe oncologic procedure. Because of reduced concern for the impact of a larger bony defect in the mandible, it has enhanced our ability to obtain clear margins at the time of resection.48 Finally, it has greatly affected the management of osteoradionecrosis of the mandible and maxilla, where the resection of the diseased bone can be followed by immediate replacement. The use of vascularized bone in this hostile recipient bed is a critical factor in achieving a successful result.

Skull Base Reconstruction

Advances in imaging for tumor mapping as well as the introduction of new techniques for safe surgical access during the last decade have had a significant impact on skull base surgery. The reconstruction of most anterior and lateral skull base defects was dependent on vascularized pedicled tissue such as local pericranial flaps, temporalis muscle, or nonvascularized fat. Although pedicled myocutaneous flaps have also been used, an inherent restriction in reach limited their applicability. Surgical extirpation of lesions located in the central skull base or those resulting in an extensive defect were often associated with a high morbidity, and hence, were considered surgically unresectable. Partitioning the contaminated sinonasal compartment from the brain remained a reconstructive problem that limited the use of surgical extirpation as a treatment for extensive tumors involving the cranial base. With the institution of free tissue transfer, vas-cularized tissue could, for the first time, be reliably transferred to the central skull base for the closure of complex defects.

A number of different free flap donor sites50 have been used for the closure of skull base defects, with the rectus abdominis probably the most frequently used. Urken et al.51 demonstrated its reliability while others have reported on its versatility for complex cranial base defects.52 The bulk associated with this myocutaneous flap is ideal for large central defects with extensive "dead space." In contrast, smaller, centrally located basi-cranial defects may be addressed with a deepithelialized radial forearm free flap. The thin, more pliable tissue characteristic of the forearm free flap provides an excellent source of vascularized soft tissue to repair dural defects, and its long vascular pedicle facilitates central skull base reconstruction requiring a distant vascular anastomosis. Irrespective of the donor site, the main objective of cranial base reconstruction is to separate the central nervous system (CNS) from the sinonasal cavity. When compared with local and pedicled flaps, free flap reconstruction has been demonstrated to be the safest and most economical method for skull base reconstruction,53 offering the best outcomes after extensive surgical resections.54

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