Lateral Segmental Mandibular Defects

Lateral segmental mandibular defects (posterior to the mental foramen) tend to be less morbid than anterior arch defects in terms of both aesthetics and function. Failure to reconstruct this part of the mandible results in a mild to moderate contour deficiency, mandibular drift toward the side of the defect, and malocclusion. The functional deficits with regard to speech and swallowing are often related more to associated soft tissue deficits and radiation therapy (7).

The best method to reconstruct lateral segmental defects is controversial. Based on past clinical experience with lateral composite resections, a regional flap (e.g., the pectoralis flap) can function as a mandibular spacer, preventing significant mandibular drift and contour deformities. However, a regional flap may not be ideal for the intraoral soft tissue component of the defect. The remaining choices for primary reconstruction of lateral segmental defects include pedicled vascularized bone, MRPs, and microvascular bone transfers. Pedicled vascularized bone tends to undergo avascular necrosis as previously mentioned. An MRP covered with a regional flap (e.g., pectoralis major) has been shown to have high plate exposure and extrusion rates. This problem was improved by using microvascular free tissue (e.g., radial forearm, parascapular, or rectus abdominis) (Fig. 8), however, problems of plate exposure persist if the associated soft tissue defect is large. Vascularized bone under an MRP or other means of rigid fixation (mandibular plates or wires) demonstrates long-term implant retention and avoids soft tissue contour deformities and plate exposure or breakage (8) (Fig. 9). The iliac crest composite flap is useful for lateral mandibular defects. The height of the bone nearly matches that of native mandible and the internal oblique muscle can be draped over the neoalveolus to provide a very thin gingivalike covering. The ipsilateral hip can be used to reconstruct a lateral mandibular defect to orient the vessels into the posterior neck (Fig. 10). As an alternative, a scapular composite flap is used and the attached skin paddle draped over the neoalveolus and lateral floor of mouth (Fig. 11). An MRP alone may be appropriate in patients who do not desire the potential for full dental restoration, have a very poor prognosis, or are unsuitable candidates for microvascular bone transfer (Fig. 12). If an MRP is used alone, a locking screw-type plate is preferred with a minimum of three screws placed at the proximal and distal ends. This type of plate has several advantages over the older AO stainless steel plates, including less breakage, loosening of screws, and absorption of bone under the plate. However, the problem of plate exposure persists and is the most common complication associated with locking screw-type plates.

Lateral resections that include the condyle represent a special problem since no proximal segment of mandible is available for rigid fixation of plates or grafts. Failure to bring the reconstruction up to the glenoid fossa may result in lateral mandibular instability, drift, and malocclusion. Condylar prostheses connected to plates or

Figure 9 A reconstructed lateral mandibular defect using a composite fibular flap. Note the bone in place with the attached skin island that will be rotated into the oral cavity over the neoalveolus.
Figure 10 Ipsilateral iliac crest harvest to orient the donor vessels into the ipsilateral neck. The muscle is used to cover the neoalveolus and the skin paddle is used to resurface external chin and neck defects.

grafts have been associated with extrusion and erosion into the middle cranial fossa. -g

A free microvascular graft can be placed near the glenoid fossa with stacked cartilage |

or fascia; however, the results of this reconstruction are uncertain and joint ankylosis ยป

may occur. A viable option is to remove the condyle from the specimen (since it is c rarely involved in the malignant process) and rigidly fixate it to the proximal end ^

of free vascularized bone (condylar autotransplantation) (9). This assumes that the >3 malignant process and mandibular resection has extended up the ramus to preclude leaving an adequate length of condyle for plating. Another alternative is o to harvest a costochondral graft from the sixth or seventh rib and affix it to the proximal end of the vascularized graft. The costochondral graft is molded into the

Figure 11 A scapular composite flap for reconstruction of a lateral mandibular defect. The skin component is used to cover the neoalveolus and close the through-and-through defect of the lateral floor of mouth.
Figure 12 An MRP used to reconstruct a lateral mandibular defect in a patient with a very poor prognosis.

shape of a condyle and seated into the glenoid fossa; intermaxillary fixation for 3-4 weeks facilitates capsule formation around the graft (10). If the condyle is not to be reconstructed, the graft should be left well short of the glenoid fossa to prevent impairment of mouth opening and ankylosis.

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