Virtual surgical planning for custom TMJ prosthetic joint replacement with simultaneous orthognathic surgery
Problem
Virtual surgical planning (VSP) has been shown to be an accurate, time-saving alternative to model surgery and splint fabrication for orthognathic surgery.1 Occasionally, total temporomandibular joint replacement is necessary to restore vertical dimension to the condyle-ramus unit in patients undergoing bimaxillary surgery.2
Traditionally, a custom TMJ prosthesis is designed and fabricated based on a stereolithographic model obtained from the patient's CT scan. Unfortunately, there is gross inaccuracy of the teeth and occlusion, which is a result of the spacing of the CT slices, dental restorations causing scatter, and patients having their teeth closed during the scan. Furthermore, if other osteotomies are required, then model surgery must be performed on the stereolithograhic model. This process is time consuming, cumbersome and can only be performed once.
VSP can be used during the design process for planning of osteotomies and splint construction, facilitating custom TMJ replacement with simultaneous orthognathic surgery.
Material & Methods
This is a retrospective chart review to evaluate the results of a cohort of subjects who underwent computer aided surgical simulation for custom total TMJ replacement with and without orthognathic surgery in 2 centers between 2009 and 2013. A process of data collection for virtual surgical planning in orthognathic surgery was utilized as previously described.1 The surgery is simulated on a computer model during a web meeting between the surgeon and software engineer. After condylectomy and other osteotomies are virtually performed, a stereolithographic model is created with the maxilla, mandible and teeth in their final virtual position. After surgeon approval, this model is transferred directly to the TMJ prosthesis manufacturer and it is used for fabrication of the custom prosthesis. The accurate placement of the condyle/ramus osteotomy is assisted either by a custom cutting guide or with an intraoperative navigation system. The virtual plan is transferred to the patient via the intermediate splint after mandibular osteotomies are performed. The custom joints are placed into position, and the maxillary osteotomies are then completed and final occlusion established. The accuracy of this method was analyzed with 3-D superimposition of the planned computer model and actual result from the post-operative CBCT. Microsoft Excel was used to ascertain descriptive statistics.
Results
Five consecutive subjects with complex craniofacial/dentofacial deformity were identified who underwent computer aided orthognathic surgical simulation combined with custom TMJ prosthetic replacement. Three patients had loss of vertical dimension secondary to trauma or end-stage internal derangement, and two patients had craniofacial microsomia with Kaban type 2 mandibular deformity. Four of the subjects underwent unilateral TMJ replacement with simultaneous bimaxillary orthognathic surgery and one patient had unilateral TMJ replacement alone. All subjects were successfully treated in one stage, with favorable changes in facial balance and functional occlusion. Postoperative CT images were compared to the virtual plan, which demonstrated a high degree of accuracy (figure 1).
A 
B 
Figure 1. Superimposition of planned and actual outcomes for patient undergoing left TMJ prosthetic replacement alone (A) and left TMJ prosthetic replacement with right BSSO and Lefort 1 (B).
Conclusion
Virtual surgical planning has allowed for an accurate and time-saving method for planning custom TMJ prosthetic reconstruction with or without simultaneous orthognathic surgery.
References
1. Hsu SSP, Gateno J, Bell RB, Hirsch DL, Markiewicz MR, Teichgraeber JF, Zhou X, Xia JJ. Accuracy of computer-aided surgical simulation protocol for orthognathic surgery: a prospective multicenter study. J Oral Maxillofac Surg 71: 128-142, 2013.
2. Dela Coleta KE, Wolford LM, Goncalves JR, dos Santos Pintos A, Pinto LP, Cassano DS. Maxillo-mandibular counterclockwise rotation and mandibular advancement with TMJ concepts total joint prosthesis. Part 1 – skeletal and dental stability. Int J Oral Maxillofac Surg 2009; 38: 126-138.