Conformity of the Actual to Planned Result in Orthognathic Surgery
Kyle Gabrick, MD, MHS, Alexander Wilson, BS, Andrew T. Timberlake, Ph.D., Rajendra Sawh-Martinez, MD, MHS, Sarika Madari, BS, Derek Steinbacher, MD, DMD.
Yale University, New Haven, CT, USA.
PURPOSE: Virtual surgical planning (VSP) has dramatically improved the workflow process for orthognathic surgery. Qualitative evidence suggests improved surgical efficiency, and splint accuracy. However, the translation from the 3D plan to the actual result, has not been adequately examined quantitatively. The purpose of this study was to compare the planned to the actual 3-dimensional result, comparing placement precision of the maxillomandibular complex in space. We hypothesize the greatest conformity exists in the anteroposterior dimensions.
METHODS: This was an HIC-approved retrospective study of patients who underwent Le Fort I maxillary advancement, bilateral sagittal split osteotomies, and genioplasty using VSP. The preoperative planned 3D file (.stl) was imported into Mimics (Materialise, Leuven, Belgium), for manipulation. Postoperative cone beam CT scans were converted, and imported into the same digital platform. Registration between the two-sets was performed using non-changed landmarks (including, mastoid, styloid, and the orbitozygomatic region). Overall bony position was then assessed, as were 3D linear and angular measurements (including: A point, B point, Pg, Me, ANS, SNA, SNB, and ANB). Multiple instances of each measure were taken, and inter-rater reliability measured. Differences were compared using t-tests, with p <0.05 being statistically significant.
RESULTS: Over 200 patients met criteria for evaluation over a 2-year period, who underwent Le Fort I, bilateral sagittal split osteotomies, and genioplasty. A subset of these were examined 3-dimensionally and compared. Three-dimensional analysis showed differences between the plan and outcome for the following landmarks in the x, y, and z dimensions: A point (x = 1.23mm, p=0.09; y=1.34mm, p=0.04; z=1.74, p=0.04), B point (x=1.32, p=0.07; y=2.15, p=0.02; z=1.67, p=0.02), Pg (x=1.24, p=0.07; y=3.71, p=0.04; z=2.12, p=0.06), Me (x= 2.62, p=0.02; y=3.95 p=0.008; z=2.40, p=0.03), and ANS (x= 1.12, p=0.04; y=1.20 p=0.04; z=1.71, p=0.005). The mean difference in angles were as follows: SNA (1.19O, p=0.06), SNB (1.29O, p=0.01), ANB (1.58O, p=0.04).
CONCLUSION: This studied reveals, that despite 3D planning with splint accuracy, there were small deviations in actual bony positioning compared with the planned position. These were more apt to occur in the transverse and vertical planes, but some difference was noted sagittally in all cases. The differences may be due to intraoperative aesthetic judgements pertaining to the vertical position and midline. Additionally, pitch alteration could influence the relative sagittal placement. The relationship of bone to soft-tissue cannot always be predicted during the VSP, and freedom for manipulation should be left to the surgeon's eye.
Back to 2018 Program