Virtual Surgical Planning in Condyle Reconstruction of Posterior Mandibulectomy Defects

Ameloblastoma is a rare neoplasm originating from proliferating odontogenic epithelium within a fibrous stroma. While these tumors are benign, they are locally aggressive and have a high tendency to recur.¹ Ameloblastoma makes up approximately 1% of all oral tumors and approximately 10% of odontogenic tumors.² These are typically slow growing but can be extremely destructive due to their propensity for local invasion. Involvement of the mandible often results in significant aesthetic concerns including development of facial asymmetry, dental involvement with resultant malocclusion, and the possibility of pathologic fractures.² There are 4 subtypes of ameloblastoma: solid/multicystic, extraosseous/peripheral, desmoplastic, and unicystic.¹

Treatment for ameloblastoma often involves surgical resection because local treatment options such as curettage carry unacceptably high recurrence rates. Curettage for multicystic tumors carries a recurrence rate of 90% to 100%; however, this decreases to 13% to 15% after complete surgical excision with wide margins.³ Because of the high rate of recurrence of this subtype, typical resection margins for solid/multicystic ameloblastoma masses extend 1.5 to 2 cm beyond the radiologic tumor border. Resection is commonly followed by immediate reconstruction and dental rehabilitation. 

Because approximately 80% of ameloblastoma tumors occur in the mandible, segmental or hemimandibulectomy followed by free flap reconstruction has become commonplace in the definitive treatment of these tumors.^4-7 Due to its long pedicle, ability to include skin and muscle, and the considerable length of bicortical bone available; the fibula free flap is the initial choice for most surgeons performing mandibular reconstruction.^8-9 However, mandibular reconstruction remains challenging due to the significant mobility of the lower jaw and the necessary precision of contour and shape of the reconstruction to restore facial aesthetics. Historically, positioning and structure of the free fibula reconstruction was based solely on the surgeon’s experience and visual spatial skills. However these operations can vary in difficulty of precision, and inaccuracies can result in malocclusion and unfavorable postoperative patient appearance.¹⁰ The advent of virtual surgical planning (VSP) using computed tomographic (CT) data to create models via 3-dimensional (3D) printing has allowed for increased accuracy of reconstruction.¹¹ This technique involves preoperative CT scans of the patient with simulation of the proposed surgical resection, and computer-assisted design of reconstructive plates needed to fashion the fibula free flap into a reconstructed mandible. 

Tumor involvement of the temporomandibular joint (TMJ) adds an additional layer of complexity to the proposed mandibular reconstruction due to the need for a stable and functional joint while avoiding restricted jaw opening. Multiple surgical options for TMJ reconstruction have been described including alloplastic prostheses, metallic condylar head attachments to reconstructive plates, distraction osteogenesis, and use of both vascularized and nonvascularized bone grafts.^12,13 Another consideration in these cases is the restoration of sensation to the overlying skin of the lower lip and jaw when tumor resection involves excision of the inferior alveolar nerve. Direct nerve repair or reconstruction with nerve allograft is often used to restore sensation postoperatively.¹² The goal of this study was to examine postoperative results in patients undergoing segmental mandibulectomy inclusive of the mandibular condyle that were reconstructed with VSP-guided free fibula flaps and inferior alveolar nerve reconstruction.

A retrospective review of patients surgically treated for giant ameloblastoma (tumor >4 cm) at the University of Mississippi Medical Center was examined for patients with posterior tumors involving the ramus and condyle. Three patients who underwent tumor resection including the mandibular condyle followed by free flap reconstruction were included. Reconstruction in all patients was performed using fibula free flap and VSP custom-made mandibular reconstruction plates. In these patients, the fibula segment that would become the reconstructed ramus was shortened and precise contouring was performed with a burr to recreate the native condylar surface. Intermaxillary fixation (IMF) using elastics was utilized to maintain dental occlusion for 1 month postoperatively. Inferior alveolar nerve repair with allograft and nerve connectors was performed for all 3 patients (Figure 1).

A healthy 16-year-old male was referred for a large primary neoplasm affecting the entire right hemimandible, with extension up to the condyle and down to the right parasymphysis. He was initially seen by an oral surgeon 4 years prior with a large right posterior mandibular mass which was biopsied and returned as unicystic ameloblastoma. He was subsequently lost to follow-up and returned to clinic 4 years later with significant right facial swelling and palpable bony expansion along the buccal and lingual surface of the right posterior mandible. Panoramic tomography was performed showing a large radiolucent lesion within the right mandibular angle and body. CT of the mass showed a large, expansile multiloculated heterogeneous mass extending from the neck of the mandibular condyle to tooth 29 with a radiographic appearance compatible with ameloblastoma. Written consent was obtained from patient when he reached age 18 for inclusion of patient photographs in this report (Figure 2).

Biopsy of the mass showed plexiform ameloblastoma, granular cell variant. After computed tomography angiography (CTA) of the bilateral lower extremities was obtained showing normal vascular anatomy bilaterally, the decision was made to proceed with segmental mandibulectomy and right free fibula mandibular reconstruction using VSP. Three-dimensional CT imaging and computer-assisted design (3D Systems) were used to plan the resection and subsequent reconstruction. The customized mandible reconstruction plate was manufactured by Stryker (Figure 3).

The ablative team performed a tracheostomy followed by segmental mandibular resection utilizing a submental visor incision. Resected area included the entire right hemimandible extending up to the condyle. Resection of the floor of mouth and gingival mucosa was performed to allow for complete tumor extirpation. Frozen section analysis was performed, and margins were negative for residual neoplasm. The right mental nerve was then reconstructed using cadaveric allograft nerve surrounded by nerve connector (Axogen) and coapted to the inferior alveolar nerve on the right. 

The right fibula was simultaneously harvested by the reconstructive team under tourniquet control. A skin paddle was designed to correspond with the resultant intraoral defect. Prior to division of the peroneal vascular pedicle, the fibula was contoured and secured to the reconstruction plate. The mandibular reconstruction plate was a 2.7-mm locking plate designed using VSP to secure a 3-segment fibula flap with closing osteotomies that were fixated into position using unicortical locking screws. The proximal aspect of the fibula that would assume the form of the reconstructed mandibular condyle was precisely contoured using a burr to create a smooth surface resembling the native condyle; this would rest within the glenoid fossa after flap inset (Figure 4). 

Microvascular anastomosis was performed between the fibula flap vessels and the facial artery and 2 venous anastamoses. The flap was then secured to the mandible with locking screws and an implantable Doppler was placed on the artery. Finally, the flap skin paddle was inset to cover the intraoral defect and occlusion was established with IMF (Figure 5). 

The patient’s postoperative course was uneventful. He had excellent facial symmetry postoperatively with maximum interincisal opening greater than 35 mm and no deviation of the mandible on mouth opening. By 9 months after surgery, sensory function to the lower lip and chin in the mandibular division of the trigeminal nerve (V3) distribution bilaterally had returned to normal (Figure 6). 

Patients B and C underwent similar mandibular reconstruction using fibula free flap with contouring of the neocondylar surface and reconstruction of the affected inferior alveolar nerve to restore mastication, appearance, and sensation after giant ameloblastoma resection. VSP was used to guide resection, flap osteotomy sites, and nerve reconstruction in these patients. Patient C had a double-barrel reconstruction of an ameloblastoma involving the right mandibular condyle with placement of immediate dental implants (Figure 7). 

All 3 patients underwent successful mandibular reconstruction with preservation of function and improved occlusion postoperatively. Each patient presented with giant ameloblastoma involving the posterior mandible and affecting the TMJ through direct involvement of the mandibular condyle. Mean patient age was 15.7 years (range 13-18). None of the patients had medical comorbidities and all denied tobacco use preoperatively (Table 1). 

All 3 patients underwent uncomplicated free fibula flap reconstruction of the mandible after ameloblastoma resection. The mean length of hospital stay postoperatively was 9.7 days (range 8-12 days). Average follow-up duration was 379.3 days (range 141-501 days). Inferior alveolar nerve repair using nerve allograft allowed for neurosensory recovery in the mandibular division of trigeminal nerve distribution for all 3 patients. There were no flap failures or partial flap losses. One patient developed hypertrophic bone formation at the mandible reconstruction requiring operative debridement. A second patient developed pneumonia immediately postoperatively requiring antibiotics, and subsequently developed a surgical site infection at an IMF screw requiring debridement in clinic. All patients had adequate mouth opening postoperatively with maximum interincisal opening greater than 35 mm and no TMJ pain after surgery.

Reconstruction of the mandible after giant ameloblastoma extirpation requires restoration of both the osseous components and soft tissue elements to restore facial aesthetics and functional mastication. The fibula free flap is an excellent choice for reconstruction of these defects due to its large availability of cortical bone as well as the ability to include a skin paddle for intraoral lining. When neoplasms involve the mandibular condyle, the reconstruction becomes more complicated. Restoration of normal condylar anatomy is necessary in order to align with the glenoid fossa within the temporomandibular joint. There is no accepted gold standard for condyle reconstruction, however multiple approaches have been used including costochondral grafts, alloplastic prostheses, bone grafts, and free flaps.^12,13 

While costochondral grafts remain the most common autogenous graft used in reconstruction of the TMJ due to their anatomic similarities to the native mandibular condyle, this approach requires a secondary donor site in the setting of fibula free flap mandibular reconstruction.^14,15 Additionally, the risks of TMJ ankylosis, graft resorption, and irregular cartilage growth including undergrowth or overgrowth are limitations to the use of this technique.¹⁵ Similarly, alloplastic devices involving metallic condylar implants articulating with a polyethylene fossa, or metallic condylar heads articulating directly with the native glenoid fossa are commonly used. However, these carry their own risks, including exposure, infection, and erosion into the temporal or middle cranial fossa.¹⁶ Additionally, unlike the fibula free flap, which continues to grow with the patient, these alloplastic devices have a fixed size, which may result in long-term complications in pediatric patients with continued skeletal growth postoperatively.¹⁷ 

While the use of fibula free flaps for condylar reconstruction does involve potential donor site morbidity, it as an ideal flap to provide a long segment of bicortical bone for reconstruction of mandibular defects extending to the condyle. The end of the fibula flap can be easily rounded with a burr and adapted to align with the glenoid fossa to create a functional TMJ.¹⁸ Use of intermaxillary fixation allows the flap to be seated and maintained within the glenoid fossa with low rates of reported postoperative ankylosis.¹⁸ 

Another consideration in surgical planning of mandibular neoplasms is postoperative sensory disturbances. The inferior alveolar nerve (IAN), a branch of the marginal mandibular division of the trigeminal nerve, provides sensation to the mandibular gingiva prior to exiting the mental foramen to become the mental nerve and provide sensation to the ipsilateral lower lip and chin.¹⁹ Due to the location of the IAN and mental nerve, these are commonly resected with the mandibular neoplasm, resulting in anesthesia of the overlying skin and lip. Reconstruction of these nerve gaps utilizing VSP planning followed by allograft and nerve protectors has shown excellent results in neurosensory recovery after IAN resection.^20,21 Our patients showed comparable results with recovery of protective sensation in all 3 patients. 

Giant ameloblastoma involving the mandibular condyle poses a challenging problem to the reconstructive surgeon. After extirpation, these defects often require restoration of a large length of cortical bone, recreation of the bicondylar articulation of the temporomandibular ginglymoarthrodial joint, and recovery of protective sensation in cases of inferior alveolar nerve resection.^22,23 This complex problem can be successfully treated with the fibula free flap utilizing mandibular reconstruction plates, VSP, and shaping of the fibula flap to recreate the dimensions of the native mandibular condyle. This technique allows for excellent restoration of occlusion and neurosensory recovery when paired with reconstruction of the inferior alveolar nerve at time of reconstruction using a combination of nerve allograft and nerve protectors. This case series highlights the use of virtual surgical planning, neocondyle creation by fibula flap burring to articulate with the glenoid fossa, and use of nerve allograft and nerve protectors to restore sensation in the mental nerve distribution. Overall, all patients included in this study had improved facial aesthetics, appropriate dental occlusion, and retained protective sensation postoperatively.