Clinical feasibility of computer-aided surgical simulation (CASS) in the treatment of complex cranio-maxillofacial deformities.

PURPOSE: The purpose of this study was to establish clinical feasibility of our 3-dimensional computer-aided surgical simulation (CASS) for complex craniomaxillofacial surgery. MATERIALS AND METHODS: Five consecutive patients with complex craniomaxillofacial deformities, including hemifacial microsomia, defects after tumor ablation, and deformity after TMJ reconstruction, were used. The patients' surgical interventions were planned by using the authors' CASS planning method. Computed tomography (CT) was initially obtained. The first step of the planning process was to create a composite skull model, which reproduces both the bony structures and the dentition with a high degree of accuracy. The second step was to quantify the deformity. The third step was to simulate the entire surgery in the computer. The maxillary osteotomy was usually completed first, followed by mandibular and chin surgeries. The shape and size of the bone graft, if needed, was also simulated. If the simulated outcomes were not satisfactory, the surgical plan could be modified and simulation could be started over. The final step was to create surgical splints. Using the authors' computer-aided designing/manufacturing techniques, the surgical splints and templates were designed in the computer and fabricated by a stereolithographic apparatus. To minimize the potential risks to the patients, the surgeries were also planned following the current planning methods, and acrylic surgical splints were created as a backup plan. RESULTS: All 5 patients were successfully planned using our CASS planning method. The computer-generated surgical splints were successfully used on all patients at the time of the surgery. The backup acrylic surgical splints and plans were never used. Six-week postoperative CT scans showed the surgical plans were precisely reproduced in the operating room and the deformities were corrected as planned. CONCLUSION: The results of this study have shown the clinical feasibility of our CASS planning method. Using our CASS method, we were able to treat patients with significant asymmetries in a single operation that in the past was usually completed in 2 stages. We were also able to simulate different surgical procedures to create the appropriate plan. The computerized surgical plan was then transferred to the patient in the operating room using computer-generated surgical splints.

Cost-effectiveness analysis for computer-aided surgical simulation in complex cranio-maxillofacial surgery.

PURPOSE: The purpose of this study is to assess the costs and benefits of computer-aided surgical simulation (CASS) and to compare it with the current surgical planning methods for complex cranio-maxillofacial (CMF) surgery. MATERIALS AND METHODS: The comparison of methods applies to all CMF surgeries where the patient's condition is severe enough to undergo a computed tomography scan and a stereolithographic model is necessary for the surgical planning process. The costs for each method can be divided into time and other costs. The time was estimated based on the authors' experience as well as on a survey of a small group of 6 experienced CMF surgeons in the United States. The other costs were estimated based on the authors' experience. RESULTS: CASS has lower costs in terms of surgeon time, patient time, and material costs. Specifically, total surgeon hours spent in planning are 5.25 hours compared with 9.75 for current standard methods. Material and scanning costs are Dollars 1,900 for CASS compared with about Dollars 3,510 for standard methods. Patient time for planning is reduced from 4.75 hours to 2.25 hours with CASS. The reduction in both time and other costs remains when the fixed fee costs of CASS are added to the variable costs. Amortized across the 600 patients per year (1,800 for the assumed 3-year life of the training and software), this adds only a few dollars and a fraction of an hour per surgery. Even in the case of a small clinic when the cost is amortized for 6 patients per year (18 patients for the assumed 3-year life of the training and software), the per surgery costs (9.65 hours and Dollars 2,456) will still favor CASS. CONCLUSION: Any great new design should consist of at least 2 of the 3 following features: faster, cheaper, and better outcome. This analysis demonstrates that CASS is faster and less costly than the current standard planning methods for complex CMF surgery. Previous studies have also shown that CASS results in better surgical outcomes. Thus, in all regards, CASS appears to be at least as good as the current methods of surgical planning.

The accuracy of cephalometric tracing superimposition.

PURPOSE: The purpose of this study was to compare the accuracy of 4 methods for cephalometric tracing superimposition. They are the FH@Porion method, S-N@Sella method, least-squared averaged 5 landmarks (LS-5) method, and manual geometric method. MATERIALS AND METHODS: Eight lateral cephalometric radiographs were used. Cephalometric tracing was performed by 2 examiners. One had extensive experience in landmark digitization while the other had minimal experience. The radiographs were scanned and the reference landmarks ANS, Point A, Point B, and Pogonion were digitized, creating 8 master tracings. Then 6 digital copies of each master tracing were made, 3 for each examiner. Subsequently, the examiners were asked to digitize and trace predetermined cranial base landmarks and structures. Tracings occurred at 1-month intervals. As a result, 3 separate tracings of each set were obtained from each examiner. The tracings of each set were superimposed using 4 different methods in the CASSOS software (SoftEnable Technology Ltd, Hong Kong SAR, China). For each method of superimposition, the coordinates of ANS, Point A, Point B, and Pogonion were recorded. Their means and variances were calculated. The variance represents the variability of the superimposition method. A general linear model for repeated measures was computed to test whether there were statistically significant differences among the 4 superimposition methods, 2 examiners, 4 reference landmarks, and 2 directions. Because the distribution of the variances was skewed, they were transformed to log variances. Finally, the errors of the superimposition in millimeters for each given examiner, superimposition method, reference landmark, and direction (X, Y) were calculated. RESULTS: There was a statistically significant difference in measurement variability among the 4 superimposition methods (P < .001). For both examiners, the variability of the different superimposition methods from the highest to the lowest was: Frankfort Plane registered at Porion method, Sella-Nasion registered at Sella method, least-square averaged 5 landmarks method, and the manual geometric method. In addition, there was a statistically significant difference in the magnitude of superimposition errors between the 2 examiners (P < .001). The experienced examiner was consistently more precise than the inexperienced examiner across all methods. Moreover, there was a statistically significant difference among 4 reference landmarks (P < .001). For both examiners, the recorded variability of each given reference landmark from the lowest to the highest was: ANS, Point A, Point B, and Pogonion. Furthermore, the variability differences between horizontal and vertical directions did not reach a conventional level of significance (P = .123). Finally, the recorded errors in millimeters for each superimposition method were summarized. A smaller error in millimeters represented a higher accuracy in superimposition. The error of using manual geometric or LS-5 methods for both examiners was less than 0.50 mm, while the error of using the other 2 methods was up to 0.99 mm for the experienced examiner and 2.88 mm for the inexperienced examiner. CONCLUSION: The error of both manual and LS-5 methods was within 0.5 mm. The LS-5 method had its advantage because it could be automated by the computer.