What Is the Linear Accuracy of Regional Voxel-Based Registration for Orthognathic Surgery Landmarks?

What is the angular accuracy of regional voxel-based registration for segmental Le Fort I and genioplasty osteotomies?

Among the accuracy analysis techniques for orthognathic surgery, regional voxel-based registration (R-VBR) has robust data, but remains unvalidated for smaller jaw segments. The purpose of this study was to validate the angular accuracy of R-VBR for segmental Le Fort I (SLFI) and genioplasty osteotomies. Postoperative cone beam computed tomography (CBCT) of consecutive patients with three-piece SLFI or genioplasties was rotated to a known pitch/roll/yaw (P/R/Y). Using R-VBR, a copy of the raw CBCT was superimposed onto the rotated CBCT at four mutual regions of interest (ROI): anterior, right posterior, and left posterior maxilla, and chin. The P/R/Y of each was subtracted from those of the rotated CBCT to calculate the angular error. The predictor and outcome variables were ROI and absolute angular error, respectively. The accuracy threshold was 0.5°. Ten SLFI and 34 genioplasties were analyzed based on the sample size calculation. The one-sample t-test and Wilcoxon signed rank test were applied in the analysis. The mean absolute error was 0.20-0.54° for the maxillary segments (all P ≤ 0.01) and 0.83-2.51° for the genioplasty segments (all P < 0.001). R-VBR has variable angular accuracy for SLFI osteotomies and may be insufficient for genioplasty. The findings may allow the design and interpretation of studies on SLFI and genioplasty with greater rigor, thereby contributing to minimizing the discrepancy between planned and achieved outcomes.

Evaluation of a Fully Digital, In-House Virtual Surgical Planning Workflow for Bimaxillary Orthognathic Surgery

BACKGROUND

The advantages of virtual surgical planning (VSP) for orthognathic surgery are clear. Previous studies have evaluated in-house VSP; however, few fully digital, in-house protocols for orthognathic surgery have been studied.

PURPOSE

The purpose of this study was to evaluate the difference between the virtual surgical plan and actual surgical outcome for orthognathic surgery using a fully digital, in-house VSP workflow.

STUDY DESIGN, SETTING, SAMPLE

This is a prospective cohort study from September 2020 to November 2022 of patients at the Victoria General Hospital in Halifax, NS, Canada who underwent bimaxillary orthognathic surgery. Patients were excluded if they had previously undergone orthognathic surgery or were diagnosed with a craniofacial syndrome.

MAIN OUTCOME VARIABLES

The primary outcome variables were the mean 3-dimensional (3D) (Euclidean) distance error, as well as mean error and mean absolute error in the transverse (x axis), vertical (y axis), and anterior-posterior (z axis) dimensions.

COVARIATES

Covariates included age, sex, and surgical sequence (mandible-first or maxilla-first).

ANALYSES

The primary outcome was tested using Z and t critical value confidence intervals. The P value was set at .05. The 3D distance error for mandible-first and maxilla-first groups was compared using a 2-sample t-test as well as analysis of variance.

RESULTS

The study sample included 52 subjects (24 males and 28 females) with a mean age of 27.7 (± 12.1) years. Forty three subjects underwent mandible-first surgery and 9 maxilla-first surgery. The mean absolute distance error was largest in the anterior-posterior dimension for all landmarks (except posterior nasal spine, left condyle, and gonion) and exceeded the threshold for clinical acceptability (2 mm) in 16 of 23 landmarks. Additionally, mean distance error in the anterior-posterior dimension was negative for all landmarks, indicating deficient movement in that direction. The effect of surgical sequence on 3D distance error was not statistically significant (P = .37).

CONCLUSION AND RELEVANCE

In general, the largest contributor to mean 3D distance error was deficient movement in the anterior-posterior direction. Otherwise, mean absolute distance error in the vertical and transverse dimensions was clinically acceptable (< 2 mm). These findings were felt to be valuable for treatment planning purposes when using a fully digital, in-house VSP workflow.

Virtual Surgical Planning of Superior Orbital Rim Fractures in Calvarial and Maxillofacial Trauma

BACKGROUND

Superior orbital rim fractures are challenging fractures as they often concomitantly occur with additional calvaria fractures. Virtual surgical planning (VSP) has been underutilized in this area of craniomaxillofacial trauma for reconstruction.

PURPOSE

The purpose of this study is to qualitatively describe the use of VSP and anatomically perfected stereolithic models in treatment of superior orbital rim fractures in combined neurosurgery/oral and maxillofacial surgery cases.

STUDY DESIGN, SETTING, SAMPLE

This study is a retrospective case series of subjects who were treated at the Massachusetts General Hospital (July 2022 to November 2022). Inclusion criteria include subjects who had both calvaria and maxillofacial injuries requiring concurrent operative intervention on their superior orbital rim fractures and the use of VSP.

PREDICTOR/EXPOSURE/INDEPENDENT VARIABLE

Not applicable.

MAIN OUTCOME VARIABLE

The outcome variable of interest is the difference in the planned position of the orbital rim repair compared to the actual position achieved.

COVARIATES

None.

ANALYSES

Heat map analysis was used to compare the difference in the planned position versus the actual position achieved.

RESULTS

There were six orbits (five subjects, mean age 33.8 ± 21.49 years) that met the criteria. The mean difference in planned versus actual orbital volume achieved was 2.52 ± 2.48 cm³. The superimposition of the postoperative scan to the planned simulation revealed 84% ± 3.27% of the voxel surface was within +2 and -2 millimeters of its planned position.

CONCLUSION AND RELEVANCE

This study has demonstrated the use of VSP in combined neurosurgery and oral and maxillofacial surgery procedures in the fixation of superior orbital rim fractures. This case series highlights that the postoperative position achieved in the six orbits was within 84% of the planned position.