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Current Practice and Future Trends in Craniomaxillofacial Reconstructive and Corrective Microvascular Bone Surgery
Hubert Weinberg, Lester Silver, and Jin K. Chun
The introduction of vascularized bone grafting has dramatically improved the potential for reconstruction of complex defects of the mandible, and it has improved the results of surgical restoration of the midface and cranial regions following tumor ablation or severe trauma. The reconstruction of the mandible in particular had been fraught with many difficulties, especially by the unfavorable milieu caused by oral contamination. The requirements of the reconstructed mandible include the maintenance of structural integrity for mastication, the successful union of adjacent bone segments, and the continued mobility of the jaw.1 Reconstruction of the midface and cranium, on the other hand, has different requirements for accurate three-dimensional stable bony replacement. The replacement bone in this region must often be thin and pliable to provide the proper shape and size.2
The first vascularized bone grafts (VBGs) were described for lower-extremity reconstruction by Taylor et al.3 and Buncke et al.4 Shortly thereafter, McKee5 described the microvascular rib transposition for mandibular reconstruction. Since then, there have been numerous studies both of the head and neck and of the extremities, which have examined the relative merits of vascularized and nonvascularized bone grafts. While nonvascularized bone heals by resorption and creeping substitution, vascularized bone maintains live cells that are capable of regeneration and provides immediate structural support.6-8 In addition, vascularized bone has been shown to continue to survive in a radiated bed with evidence of callus formation and a fully viable bone marrow with new bone formation in the subperiosteal and endosteal layers.9
Mandibular Reconstruction
Absolute indications for reconstructing the mandible with VBGs were given by Chen et al.10 and include: (1) osteoradionecrosis of the mandible or an irradiated tissue bed; (2) hemimandibular reconstruction with a free and facing glenoid fossa; (3) long segment mandibular defect, especially across the symphysis; (4) inadequate skin or mucosal lining; (5) defects demanding sandwich reconstruction; (6) inability to ob-
tain secure immobilization on the reconstructed unit; (7) failure of reconstruction by other methods; and (8) near-total mandibular reconstruction. The advantages of VBGs in these settings have been clearly demonstrated in extensive clinical studies. The early success rate in these studies has exceeded 90%, further demonstrating the safety and reliability of mandibular reconstruction with vascularized bone.11,12
The ideal qualities of the vascularized bone graft for mandibular reconstruction have been described by Urken.13 It should be well vascularized; of sufficient length, width, and height; easily shaped without compromise to its vascularity; accessible for a simultaneous two-team approach; and have minimum donor site morbidity. Particularly for the mandible, the ideal qualities of the composite soft tissue requirements also need to be considered. The soft tissue component should be again well vascularized, thin, pliable, abundant, sensate if possible, and well lubricated. Often it is the soft tissue component and not solely the restoration of bony continuity that will determine the ultimate success of the mandibular reconstruction. The soft tissue may be needed to restore external neck or facial skin, and it may be required for mucosal replacement of the mandible, tongue, or pharynx. Soft tissue reconstruction should maintain tongue mobility and allow unimpeded swallowing and articulation.
The choice of donor sites available for mandibular reconstruction includes the iliac crest, fibula, scapula, metatarsus, cranium, rib, radius, ulna, and humerus. At present, in the vast majority of mandibular reconstructions, the iliac crest, fibula, or scapula is used. The iliac crest has proven to provide the best bone stock, especially for primary placement of endosseous dental implants (Figure 26.1).14 A modification of the iliac crest osteomyocutaneous free flap including the internal oblique muscle has been described.15–17 This latter muscle provides thin, well-vascularized soft tissue that upon denervation atrophy approximates the appearance of mucosa. The fibula provides the greatest bone length of all the VBGs and can be contoured to that of a mandible with numerous osteotomies (Figure 26.2).18 The height of the fibula is, however, somewhat restrictive in its capacity to accept an endosseous implant, although it can be sectioned and double-
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FIGURE 26.1 Deep circumflex iliac artery osteocutaneous flap. (a) Flap design. (b) Harvested flap in situ. (c) Flap inset with rigid fixation.
(d) Postoperative result.
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FIGURE 26.2 Fibula osteocutaneous flap. (a) Flap design. (b) Har- (e) Postoperative result. vested flap with osteotomized segments and miniplate fixation
in situ. (c) Postoperative posterior-anterior radiograph. (d) Postoperative technetium-99 bone scan demonstrating vascular uptake.
26. Current Practice and Future Trends in Craniomaxillofacial Reconstructive and Corrective Microvascular Bone Surgery |
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layered to increase its height, as in the double-barrel technique.19,20 The cutaneous segment of the fibula flap may also at times prove to be unreliable. The scapula flap has an excellent soft tissue component that makes it ideal for soft tissue restoration in the mandibular region.21 However, the bone stock available is again fairly limited as is bone length. Furthermore, because of patient positioning, a two-team approach is often needed, thereby increasing the difficulty of this procedure.
Craniofacial Reconstruction
The indications for use of vascularized bone grafts for craniofacial reconstruction are less well defined than in the mandible.26 The soft tissue bed in this region is well vascularized, and often autogenous, nonvascularized bone grafts and alloplastic substitutes do quite well. Furthermore, welldescribed pedicled bone flaps based on the temporoparietal fascia can be rotated into adjacent regions with little difficulty (Figure 26.3).22,23 Should the recipient bed, however, be scarred with poor vascularization and the required bony reconstruction quite large, then certainly VBGs are indicated and have been used successfully.24 Vascularized bone grafts in these circumstances have been noted to maintain contour and size very well when followed for periods ranging from 3 to 8 years.25
The choice of bone graft donor sites will depend on careful analysis of the characteristics of the defect and the corresponding characteristics of the flap. An analysis must therefore be made of the extent of bone loss, the soft tissue deficit, whether skin, mucosa, or both, and the nature of the functional derangement. Computer-generated templates have also been used to accurately predict size, contour, and orientation of the VBG.27 The choice of flap in turn must address the length of the vascular pedicle, the thickness of the soft tissue component, the mobility of the soft tissue, the dimensions and configuration of the bone in relation to the defect, and finally the associated donor site morbidity.2 Unlike the mandible, with a number of recipient blood vessels from which to choose, in the craniofacial region strong consideration must be given to the selection and location of a recipient pedicle. The facial artery and vein are often the best suited for vascular anastomoses in reconstruction of the midface, but they will probably not be of sufficient length for reconstructions of the nose and orbit. The superficial temporal vessels, while at times suitable as recipient vessels, will often be of small caliber and prove to be inadequate for microvascular anastomoses. Vein grafts may be required to achieve a sufficiently long pedicle, but this will certainly add to the time and complexity of the surgical endeavor.
Probably the most versatile VBG for reconstruction of the craniomaxillofacial region has been the scapula flap.19 The circumflex scapular artery, a branch of the subscapular supplies either a horizontal, vertical, or a combination skin pad-
dle, and also supplies the lateral border of the scapula (Figure 26.4). An angular artery, a branch of the thoracodorsal artery, can also be included in the design of the scapular flap to allow two separate vascularized bone grafts to be harvested using a single vascular pedicle.26
The iliac crest and the fibula, while useful under certain circumstances, rarely are ideal for reconstruction where thin bone and skin of good quality and color match are essential for an optimal result. Recently, reconstruction of small, thin defects of the orbital region has been accomplished with vascularized cortex taken from the medial supracondylar region of the femur.28
Current Research
To reduce the very substantial donor site morbidity inherent in most vascularized bone graft transfers, attention has recently focused on the prefabrication of vascularized bone flaps. Based on the preliminary studies of Hirase,29,30 most of these studies use a principle of staged flap reconstruction. In the initial phase of this reconstruction vascularized tissue with a large identifiable pedicle is induced to perfuse the selected bone graft donor site. The bone remains in situ until sufficient vascularization has occurred from its new pedicle that a successful transfer can be accomplished. The great advantage of this technique is that bone can be harvested from almost any site in exactly the dimensions that are required without regard to its native blood supply. The disadvantage is the necessity for two stages and the possibility that despite staging, the bone donor will still be inadequately vascularized by its new vascular pedicle.31
Another intriguing possibility was initially suggested by Nettelblad et al.32 and then more recently revised by Mitsumoto et al.33 A vascularized bone graft was formed by placing bone marrow into cylindrical hydroxyapatite chambers to which allograft demineralized bone matrix powder had been added. Those chambers that were implanted subcutaneously with implantation of a vascular bundle showed accelerated neovascularization and early bone formation. The possibility that such prefabricated and preshaped vascularized bone grafts could be used clinically for elective craniofacial reconstruction is certainly worth contemplating.
Summary
Microvascular surgery has opened numerous possibilities for single-stage reconstruction of complex deformities of the craniomaxillofacial region. Newer techniques will undoubtedly further advance the reconstructive options of the surgeon, perhaps simplifying the sometimes difficult procedures or allowing more refinement in the everlasting pursuit of perfect form and function. Surgery and creativity must continue to form a close alliance to further refine the
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FIGURE 26.3 Temporoparietal osteofascial flap-superficial temporal artery. (a) Preoperative mandibular contour defect. (b) Harvested flap in situ. (c) Transposition of flap prior to inset and rigid fixation.
