Precision Analysis of the Temporomandibular Joint in Mandibular Reconstruction Using Virtual Surgical Planning

Purpose:  Virtual surgical planning (VSP) using Computer-Aided Design and Manufacturing (CAD-CAM) have been reported to demonstrate significant improvements in craniofacial reconstruction. Complex mandibular defects requiring the free fibula osteocutaneous flap have been a point of focus in these studies. The reported improvements have been mainly related to operative performance, with limited evaluations of the functional aspect of reconstruction at the temporomandibular joint (TMJ). The purpose of this study was to review our series free fibula mandibular reconstructions using these adjunctive technologies in order to evaluate the postoperative outcomes related to the TMJ.

Methods:  This study is a retrospective comparison of patients who underwent mandibular reconstruction using a free fibula osteomyocutaneous flap with and without VSP. All patients underwent preoperative computed tomography (CT) of their mandible. The CAD-CAM group had their CT DICOM data sent to a medical modeling company in order to map the mandibular resection, virtually place the mandibular reconstruction plate, and create surgical guides. Postoperative CT’s were attained and used to evaluate the TMJ.  CT images were digitized for two- and three-dimensional analysis using surgical planning software (Materialise, Leuven, Belgium). The TMJ in patients with and without VSP were analyzed using a multiple anatomical landmarks and cephalometric relationships.

Results: A total of 16 patients who what either traditional or VSP for mandibular reconstruction were compared.  The average age was 61.6yo, with 75% male population.  81% of patients were current or former smokers.  Two groups (n=8 each) were compared for positioning of the mandibular condyle in the glenoid fossa.  Pre and post-operative position and displacement of cephalometric landmarks were compared.  Measurements of superior, anterior and lateral movements were comparable in the pre- and post-operative groups for both the traditional and VSP groups (ANOVA p<0.001). Sub-group analysis evaluating ipsilateral changes in the mandibular condyle position for traditional vs VSP noted decreased percentage of change in superior (22% vs 10%, p<0.1), anterior (32% vs 15%, p<0.1) and lateral shift (7% vs 1%, NS) of the condyle for left mandibular reconstructions (n=8).  Ipsilateral right mandible reconstruction (n=6) demonstrated changes in superior (62% vs 15%, p<0.1) and anterior shift (5% vs 9%, NS).

Conclusion:  Our data demonstrate adequate pre and postoperative positions of TMJ landmarks for traditional mandibular reconstruction and virtual surgical planned reconstructions.  Evaluation of condyle movements showed differences in ipsilateral position in pre and postoperative groups.  VSP resulted in decreased superior and lateral shift of the ipsilateral condyle, and a decreased change in the condylar and condylar neck angles.  This work demonstrates that virtual surgical planning can lead to increased precision in reconstruction leading to preserved normative anatomical relationships. 

Hirsch, D. L. et al. Use of computer-aided design and computer-aided manufacturing to produce orthognathically ideal surgical outcomes: a paradigm shift in head and neck reconstruction. Journal of oral and maxillofacial surgery : official journal of the American Association of Oral and Maxillofacial Surgeons 67, 2115-2122, doi:10.1016/j.joms.2009.02.007 (2009).

Metzler, P., Geiger, E. J., Alcon, A., Ma, X. & Steinbacher, D. M. Three-dimensional virtual surgery accuracy for free fibula mandibular reconstruction: planned versus actual results. Journal of oral and maxillofacial surgery : official journal of the American Association of Oral and Maxillofacial Surgeons 72, 2601-2612, doi:10.1016/j.joms.2014.07.024 (2014).