Master Techniques in Otolaryngology - Head and Neck Surgery: Reconstructive Surgery, 1ed.

17. Management of the Total Mandibular Defect

Peter C. Neligan

INTRODUCTION

The indications for total mandibular reconstruction are relatively rare. However, it is important to understand the principles involved so that the various segments of the mandible can be reconstructed optimally. In addition, it is relatively rare that the mandible needs to be reconstructed in isolation. Far more common is the setting in which bone reconstruction is required in combination with replacement of intraoral lining, reconstruction of the external skin envelope, or both. The most common requirement for reconstruction is that of the segmental defect, and there are principles that apply depending on which segment is involved. Boyd classified mandibular defects based on the segment of mandible involved together with the soft tissue requirement, either mucosa (m) or skin (s). This is helpful when planning reconstructions.

Mandibular reconstruction has evolved over the past three decades from a complex and often not very successful venture to a very reliable, if still complex, technique. The main reason for this advance has been the incorporation of microsurgical techniques and the development of reliable flaps for reconstruction. Of these developments, the most significant has probably been the description of the fibula as a suitable bone to achieve mandibular reconstruction. For while there are other flaps that can be used, and there are specific indications where some of these may be better, the fibula has emerged as the gold standard for mandibular reconstruction. The concept of maintaining quality of life has become particularly important in the overall care and treatment of cancer patients. Thus, even patients with a very limited life expectancy are routinely reconstructed if it is expected that their quality of remaining life would be significantly enhanced. The high success rate of head and neck reconstructive procedures has allowed for significant improvement in both functional and aesthetic results and has completely changed the conceptual approach to mandibular reconstruction. Only patients who are medically unfit to tolerate a long operation or have a grave prognosis are excluded as candidates for resection and immediate reconstruction.

Because the fibular free flap donor site is the most common donor site used for total mandibular reconstruction, the history is centered around factors that may limit the use of this donor site. Prior injury to the lower leg, peripheral vascular disease, or disturbance in gait are all issues that need to be considered in taking history from a patient who requires a total mandibular reconstruction. Prior injury to the lower leg may limit the use of the fibula bone or may have left the patient with significant gait disturbance that could become functionally devastating following a fibula harvest. Significant peripheral vascular disease commonly afflicts the lower extremities. Patients with a history of lower extremity claudication, vascular insufficiency, or poor lower extremity circulation should be carefully evaluated using lower extremity vascular imaging. Because the fibular donor site is the only bony donor site that provides the length of bone necessary for complete mandibular reconstruction, there are few alternative choices.

Reconstruction of the total mandibular defect can be performed primarily or secondarily. Arguably, the latter represents a more significant challenge than does the former because one needs to contend with the scar contractures and limited soft tissue envelope. In both cases, a careful physical examination will determine if there are remaining condyles, dentition, and an appropriate soft tissue to accommodate the vascularized bone reconstruction. In cases where the condyles are present, the design of the flap can be altered to use the remaining bone. In contrast, if the examination reveals that the condyles are not present, the distal aspects of the fibula will need to be designed to recreate the joint. The examination of the dentition is important to determine if the patient will require dental occlusal management during surgery to maintain the appropriate dental occlusion following surgery. Finally, a careful assessment of the soft tissue is important in determining if a skin paddle should be included in the design of the flap. All aspects of the examination are important; however, these issues are the most important when considering total mandibular reconstruction.

While it is true that some defects do not necessarily require reconstruction with bone, my personal bias is to reconstruct all mandibular defects with a bone flap unless there are specific patient factors that preclude that. Fortunately, this situation is rare.

The lateral mandibular defect can be reconstructed with a plate and soft tissue flap. However, if the plate fractures (and, over time, this is more likely to happen), the patient will require a further reconstruction, probably with bone. So from my perspective, it is easier to use a bone flap in the first place and avoid this problem altogether. Central mandibular defects, however, require reconstruction with bone. Use of a plate and soft tissue flap invariably results in exposure of the plate over time. This is totally avoidable if a bone flap is used and is the one situation in which use of a bone flap is mandatory.

The third area to be considered when thinking about total mandibular reconstruction is the condyle and the temporomandibular joint. Various techniques have been proposed to reconstruct the condyle. These include use of a reconstruction plate incorporating a condylar head, grafting of the existing condyle onto the bone flap used for the reconstruction, use of a costochondral graft to replace the mandibular neck and condyle, or the use of soft tissue interposition between the bony construct and the condylar fossa. My personal preference is to use interposition of soft tissue. I have used periosteum for this purpose with good results.

While there are several bone flap options for mandibular reconstruction, there is general consensus that the fibular flap is the gold standard. It combines good bone stock, adequate length, as well as soft tissue that is very suitable for most applications within the oral cavity. The length of fibula that can be harvested approaches 25 cm, sufficient length to reconstruct almost all defects. The bone stock is such that it accommodates osseoin-tegrated dental rehabilitation. One criticism, however, is that the bone height is less than that of the mandible. This can be important for fitting osseointegrated teeth. There are a number of potential solutions to this. One is to fudge the inset of the fibula so that, instead of matching the fibula with the inferior border of the mandible, the bone is inset a little higher to minimize the discrepancy between the alveolar border of the mandible and the fibula. Harvesting a cuff of flexor hallucis longus (FHL) with the bone helps to soften the interface between the mandibular border and the fibula and hides the potential step between the inferior border of the mandible and the inferior border of the fibula. Another strategy is to double barrel the fibula, stacking one segment on top of the other. This technique can be used for shorter mandibular defects, but for larger defects, it is less applicable as it uses up too much bone length. A final strategy is to vertically distract the fibula.

The mandible is an arch, while the fibula is a straight bone. In order to make an arch, multiple osteotomies may be required. The blood supply of the fibula is both endosteal and periosteal, a fact that renders it most amenable to multisegmental osteotomies and precise shaping. However, it has been shown that the more bone segments in the construct, the greater the risk of devascularization. Finally, the donor defect following fibular harvest is very acceptable despite the fact that it has been shown that there is a significant deleterious effect on foot and ankle function.

If the preoperative evaluation does not demonstrate three-vessel perfusion, the fibula is contraindicated.

The reliability of the fibular skin paddle has been controversial. Initially, there was a sense that the skin paddle was not universally reliable though there is excellent evidence that this is not the case. In the early days, it was common practice to get an angiogram of the lower limb to determine the patency of the peroneal vessels, a practice that most people abandoned. However, more recently, as our knowledge of the perfusion of the integument has improved, interest in mapping the blood supply of our flaps has undergone a renewal. The use of CT angiography has become popular in determining the blood supply of flaps. This has come from the development of perforator flaps and is a very useful tool. While it is most widely used in autologous breast reconstruction, it is equally applicable to all flaps. The CT angiogram not only can depict where the vessels are but also maps their course, their relationship to the musculature, and so on. It shows anatomic variability where, in the past, it was discovered during the dissection and while it is not necessary to have a CT angiogram in order to raise a fibular flap, it takes the guesswork out of the dissection and makes it more predictable, quicker, and probably safer. It is particularly relevant to the placement and dissection of the skin paddle. Another very useful tool in determining flap perfusion is the use of indocyanine green dye. This is a fluorescent dye that when injected intravenously can be detected using a laser light source that excites the fluorescence and near-infrared fluoroscopy that detects it. This technology is widely available. In the United States, the system is called SPY and is marketed by LifeCell Corporation (Branchburg, NJ). While this is not necessary in order to safely raise a fibular osseocutaneous flap, it is a useful tool in predicting flap viability and avoiding problems. This is particularly the case if there is any doubt as to the viability of the skin paddle.

One of the first things surgeons are concerned about is whether it matters which fibula to take for a given defect. The short answer is that for most defects it does not matter. However, there are some important things to remember. The orientations of the skin paddle and of the pedicle are the two major determining factors. The optimal relationship of the skin paddle to the bone is as it appears in the leg. So if a right-sided mandibular defect with a need for intraoral lining is being reconstructed, an ipsilateral fibula will work well and the pedicle will be at the angle of the mandible. If it is better for the pedicle to come out anterior, then a contralateral flap would work better.

It is important to mark the fibular head and the lateral malleolus and to measure back from these two points. A length of about 6 cm at either end will protect the ankle mortice distally and the peroneal nerve proximally. While it is not necessary to harvest all the intervening bone, it is easiest to do so, even if all the bone is not required. The unwanted bone can be discarded making dissection of the pedicle easier. As long as the distal and proximal 6 cm of bone are preserved, morbidity will not be a major issue.

It is important to realize that the blood supply to the skin passes in the posterior crural septum, and this structure is approximately 2 cm behind the axis of the fibula. In a thin individual, it can be appreciated on the surface of the limb. It is also important to realize that the blood supply of the peroneal skin compartment is musculocutaneous proximally and septocutaneous distally. For that reason, a skin paddle more distally placed will be more likely to have a septocutaneous blood supply. Consequently, I plan the skin paddle in the distal third (Fig. 17.1). If a second skin paddle is required, it can be dissected based on one of the more proximal musculocutaneous perforators. This is a situation where a preoperative CT angiogram is particularly useful. These vessels can also be detected with a handheld Doppler prior to beginning the dissection. However, while the Doppler will give good information on the position of the perforator, the CT angiogram gives additional information on the course of the perforator, its relationship to the musculature, and its relationship to the peroneal vessels.

FIGURE 17.1 The skin paddle is placed in the distal third to take advantage of the septocutaneous perforators. More proximal perforators are musculocutaneous. Note that this skin paddle has a dual sensory nerve supply, from a recurrent branch of the superficial peroneal nerve (SPN), and from the lateral sural cutaneous nerve (LSCN).

Regardless of the type of fibular flap being harvested, osseocutaneous or bone-only flap, my preference is to harvest the fibula through a lateral approach. Figure 17.2 demonstrates the incision lines and their relationship to the various structures in the leg. The anterior incision of the skin flap is made, and the incision is carried through the subcutaneous tissue down to the fascia. The superficial peroneal nerve (SPN) can be seen deep to the fascia and is preserved by incising the fascia just posterior to it. The fascia can then be swept off the underlying muscle with a finger, and this reveals the anterior leaf of the posterior crural septum. I generally keep all of my dissection anterior, only making the posterior skin flap incision when most of the dissection is complete. The proximal skin incision is also made at this time in continuity with the incision already described. The fibula is now approached from the lateral aspect, along the anterior leaf of the posterior crural septum, leaving some muscle fibers on the bone in order to protect the periosteum, since the fibula, aside from its endosteal supply, also has a robust periosteal blood supply. It is this periosteal supply that I mostly rely upon in maintaining viability of the bone. As soon as the lateral border of the fibula is reached, dissection then proceeds anteriorly, hugging the bone and taking care not to breach the periosteum. The next structure encountered is the anterior crural septum, and this is divided along the length of the fibula. This gives access to the anterior compartment. It is important to be aware of the fact that the anterior tibial vessels are in relatively close proximity to the dissection at this point and can potentially be damaged if care is not taken. The easiest way to avoid this is to hug the bone during the dissection. Retracting the muscles of the anterior compartment, dissection now proceeds around the fibula. The next structure encountered is the interosseous membrane, which is a very strong structure. Prior to dividing it, I like to carry out the osteotomies on the fibula. Care must be taken to preserve at least 6 cm of fibula at either end in order to protect the ankle mortice distally and the peroneal nerve proximally. Bone levers are placed behind the bone, once again, hugging the bone. I use Hohmann bone levers. The narrow end of the lever is convex, and this facilitates placing it around the bone and in close proximity to it. Then, using an oscillating saw, the osteotomies are done proximally and distally, cutting down on the bone lever in order to avoid injury to the underlying structures, and, most particularly, avoiding injury to the pedicle. Bone clamps are then applied to the fibula, and the bone is rotated laterally. This allows visualization of the interosseous membrane. This is now divided, and as it is incised, the surgeon can feel the fibula move laterally and the space between tibia and fibula open up. Next, the peroneal vessels are identified distally and are divided. The vessels lie behind the tibialis posterior muscle, and this is now split over the pedicle so that the pedicle comes into direct view, lying on the flexor hallucis longus muscle. Various muscular branches are divided as the dissection proceeds. The pedicle runs along the length of the bone, but proximally, it can be seen to deviate medially toward the tibia. Further dissection will reveal its origin, branching from the posterior tibial artery. This completes the pedicle dissection.

FIGURE 17.2 This schematic diagram of the cross-sectional anatomy of the lower limb shows the relationship of the various structures and incorporating the peroneal artery with the skin perforators traversing the posterior crural septum. The standard incisions are marked in yellow showing the structures harvested with the flap. Dotted yellow line indicates that Flexor Hallucis Longus (FHL) can be harvested with the flap if desired. (FDL, flexor digitorum longus.)

The length of bone that is required is now determined. The mandibular defect is carefully measured. It is important when translating this measurement to the fibula to remember that the mandible is curved bone and the fibula is a straight one. Osteotomies will need to be made in order to convert it to a curved bone. In general, these osteotomies are closing osteotomies. This implies that a wedge of bone has to be excised in order to create the curve, and, if a significant length of mandible needs to be replaced, multiple osteotomies may be required. To add greater complexity to total mandibular defects, these osteotomies are multiplanar and threedimensional. Not only must the curve of the mandible be reproduced but the angle of the mandible also needs to be replicated.

There are many ways to plan the osteotomies that need to be performed in order to accurately replicate the shape of the mandible. These range from free-hand guesswork (not recommended) to stereolithographic modeling and plate prebending. My personal preference is to use the native mandible as a template. The ablative team bends a reconstruction plate to the mandible prior to mandibular resection. This plate is also predrilled to the mandibular remnants. In this way, when the plate is replaced on the mandible after resection, the lateral elements of the mandible will maintain their relationship to the maxilla. Maintenance of this biarched relationship is key to successful mandibular reconstruction. In total mandibular reconstruction, simply prebending the plate will not work. In these cases, some sort of preoperative modeling is required. Stereolithographic modeling is expensive but very accurate. A model is made of the mandible from a three-dimensional CT scan. A plate is bent to this model to ensure maximal accuracy. Alternatively, a different version can be created with methyl methacrylate based on a CT scan (Fig. 17.3). This is probably less accurate, but, nevertheless, it is arguable whether these reconstructions are so unforgiving as to demand absolute precision. My personal opinion is that absolute precision is not completely necessary. This is because of the improved technology of locking plates that do not demand absolute apposition of plate to bone along the entire length of the plate, unlike nonlocking plates. What is necessary is that the arch be reasonably accurately reproduced and, probably more importantly, that the relationship of the reconstructed mandible to the maxilla replicates the relationship that existed before the resection.

FIGURE 17.3 This is a methyl methacrylate template made from patient CT scans. The plate can be prebent to this template. Stereolithographic representations can also be manufactured from CT images.

My personal technique involves determining the osteotomies based on the dimensions of the prebent plate, that is, the plate that has been bent to the existing mandible prior to resection. I try to keep my osteotomies to a minimum, reducing the number required by “rounding off’ the ends of each osteotomy segment (Fig. 17.4). Once the osteotomies have been completed and assuming there is some remnant of mandible to which I am attaching my construct, I leave the bone ends on the fibula a little longer than measured so that I can make the final adjustments as I inset the fibula to the mandible. This allows for a press fit and ensures maximal apposition of the bone.

FIGURE 17.4 A closing wedge osteotomy is designed to create a curve in the fibula. Two wedge osteotomies are shown. This curve can be further enhanced by resecting the apices of the bone cuts as shown.

From a practical point of view, I like to inset the soft tissues first, assuming that I am replacing intraoral lining. This allows easier access for once the bone is inset, access to the oral cavity is reduced. Once the soft tissue is inset, the bone fit is performed following which the microvascular anastomosis is carried out. If the flap is providing external skin cover, then this part of the inset is done last, after intraoral reconstruction and bony fit.

The patient is required to wear a lower leg donor side split for 7 days. The patient is restricted to a soft diet for 6 weeks to allow the fibular bone flap to heal.

There are many potential complications that include malunion of the bone graft, necrosis of the fibular skin paddle, and donor site morbidity including skin sloughing, foot drop, and instability of the ankle.

Mandibular reconstruction has reached a level of reliability, reproducibility, and aesthetic and functional acceptability that could not have been imagined 30 years ago. Nevertheless, it remains a complex procedure that demands attention to detail and meticulousness in its execution.

• Determine what is being resected and plan accordingly.

• Determine which fibula is most advantageous to use.

• Position skin paddle distally.

• If in doubt, do a preoperative CT angiogram.

• “Round off” osteotomies.

• When determining bone length, do not forget to take into account that the wedge osteotomies will be discarded so a greater length of bone is required.

• Determine beforehand the optimal positioning of the skin paddle relative to the bone. Remember the best relationship is what is in the leg.

• Standard head and neck surgical set

• Reciprocating saw

SUGGESTED READING

Hidalgo DA. Fibula free flap: a new method of mandible reconstruction. Plast Reconstr Surg 1989;84(1):71–79.

Boyd JB, Gullane PJ, Rotstein LE, et al. Classification of mandibular defects. Plast Reconstr Surg 1993;92(7):1266–1275.

Boyd JB, Morris S, Rosen IB, et al. The through-and-through oromandibular defect: rationale for aggressive reconstruction. Plast Reconstr Surg 1994;93(1):44–53.

Schliephake H, Neukam FW, Schmelzeisen R, et al. Long-term quality of life after ablative intraoral tumour surgery. J Craniomaxillofac Surg 1995;23(4):243–249.

Wilson KM, Rizk NM, Armstrong SL, et al. Effects of hemimandibulectomy on quality of life. Laryngoscope 1998;108(10):1574–1577.

Ko EW, Huang CS, Chen YR. Temporomandibular joint reconstruction in children using costochondral grafts. J Oral Maxillofac Surg 1999;57(7):789–798; discussion 99–800.