(15) Cutting guides in mandibular tumor ablation: Are we as accurate as we think?

Abstract: The introduction of computer-assisted surgical planning and computer-aided manufacturing in reconstructive surgery has been proven to have many advantages such as decreased operative and ischemic times and superior accuracy.(1-3) However, even with the introduction of computer-assisted surgical planning one of the main challenges is accurate positioning of the surgical cutting guide due to lack of anatomical landmarks and soft tissue interferences during placement. The purpose of this study is to determine the accuracy of osteotomy lines produced by the virtually planned three-dimensionally printed cutting guides and to assess the overall accuracy of mandibular resection using virtual planning and patient-specific reconstruction plates.
We performed a retrospective evaluation of all patients who had virtual surgical planning using IPS® KLS Martin and fabrication of 3D printed cutting guides for the ablation of mandibular pathology between July 2016 and June 2020. IRB approval was obtained from UIC (IRB #2019-0836).
A total of 23 patients who had a segmental mandibular resection and reconstruction utilizing virtual surgical planning and the Individual Patient solutions (IPS) platform were identified, fourteen patients met all the inclusion criteria. Preoperative 3D virtual models were acquired from existing CAD/CAM protocol used for virtual planning for each patient while the DICOM file from the postoperative CBCT or CT scan were processed via ProPlan CMF ® software to create postoperative 3D models comparable to the preoperative models. The pre and postoperative 3D models were transferred to 3D Slicer for alignment using the automated surface registration feature based on the iterative closest point algorithm. The models were transferred to Meshmixer to measure the deviation in the osteotomy lines. The XYZ orientation was based on the Frankfort plane, midsagittal plane (perpendicular to Frankfort and crossing the nasion-basion), and nasion. Lastly, the models were imported to MeshLab for volumetric analysis.
26 mandibular osteotomies performed utilizing 3D printed cutting guides were evaluated. Of those, 12 were on the small segment and 14 on the large residual segment. The average deviation between virtually planned osteotomy and actual surgical osteotomy of 1.52 +/-1.02mm. The difference in deviation in both small and large segments based on the defect location and classification was not significant (p-value 0.87 and 0.26 respectively). The size and class of mandibular defect was not associated with a significant variation in the deviation measurement. The mean difference between the intercondylar and intergonial distances of the pre- and post-operative models was 0.28 mm +/- 3.58 and -0.35 mm +/- 2.84 mm retrospectively. For the mandibular body length to the horizontal corner, the mean difference was 1.56 +/- 4.3 mm, and the mean difference to the midline was 0.2 +/- 2.84 mm. Additionally, the average difference in the ramus length was 0.99 +/- 2.61 mm, and the mean sagittal angle discrepancy was -0.37 +/- 4.97 degrees. None of the linear and angular measurements showed a statistically significant deviation in the surgical result compared to the virtual plan p-value > 0.05. For volume deviation, the maximum negative deviation of the postoperative mandible ranged from -8.4 to -3.8 mm3 with a mean of -6.0 +/- 1.5 mm3 while the average maximum positive deviation was 5.6 +/- 2.27 mm3 and a range of 1.8 to 9.6 mm3. There was no significant relationship between defect location or classification and volumetric deviation
Virtual surgical planning is an unambiguous paradigm shift in the predictability of the surgical plan and achievement of the reconstruction goals. The 3D printed cutting guides are a very accurate and reliable tool in translating the virtual ablation plan to an actual surgical resection margin.