(20) Validation of Andrews Analysis in the Virtual Environment

Abstract: Andrews 6 keys to orofacial harmony states the optimal sagittal position of the maxillary incisors should vertically align between the forehead midpoint and the soft tissue glabella in the anteroposterior dimension. Posnick has suggested a simplified Andrews analysis with anteroposterior alignment of the maxillary incisors with the soft tissue glabella.1 Traditionally, this measurement is carried out on facial photographs taken in the adjusted natural head position (aNHP). Resnick and colleagues confirmed the accuracy of performing Andrews analysis on 2D lateral cephalograms2 however the analysis has not been validated in the 3D virtual environment. The purpose of this study is to analyze the accuracy of Andrews analysis when performed in the virtual environment.

The investigators designed a retrospective cohort study of consecutive patients who underwent orthognathic surgery by a single surgeon at the University of Alabama-Birmingham between February 2020 and February 2022. The traditional Andrews analysis photograph was taken during the pre-surgical planning appointment. The patient was positioned into an adjusted natural head position (aNHP), a ruler was taped to the cheek to assist with calibration of the photograph, and a facial photograph was obtained with the patient smiling. This photograph was then transferred to Microsoft PowerPoint (Redmond, WA) where the digital ruler was calibrated with the ruler on the patient's cheek, and the simplified Andrews analysis was calculated. The 3D cone beam CT which was previously obtained for virtual surgical planning and archived on the KLS Martin database was accessed for retrospective measurement. The lateral facial photographs in the aNHP were imported into the virtual environment and the 3D composite model was then oriented into the aNHP. The software engineer, blinded to the traditional measurements, then performed the simplified Andrews analysis in the virtual environment. Maxillary incisors located behind the soft tissue glabella indicate the need for advancement. They were assigned as a positive value and those in front of soft tissue glabella as a negative value. The correlation coefficient was then calculated to compare the two datasets (photograph vs 3D Andrews analysis).

57 consecutive patients who underwent orthognathic surgery were evaluated. 5 patients were excluded due to the soft tissue glabella not captured on 3D CBCT and 2 were excluded for diagnosis of syndromic facial deformity. 54% were female with a mean age of 25.9 + 12.6 years. 37 (74%) of patients were White, 9 (18%) were Black, 2 (4%) were Hispanic and 2 (4%) Asian. Five (10%) patients had cleft lip and palate and 1 (2%) had isolated cleft palate. For the photographic analysis, the mean incisor-GALL distance was -0.44+ 7.12 mm with means of -1.13+7.21mm for females and +0.37+7.09mm for males. For the virtual analysis, the mean incisor–GALL distance was 0.13 + 7.21 mm with an average of -0.004mm+7.36mm for females and +0.30+7.19mm for males. The Pearson correlation coefficients between the photograph and 3D analysis was high (correlation of 0.93). When further stratified, the only correlations not rated as very strong (>0.90) were for: caucasian patients (0.89) and patients with a history of cleft lip/palate (0.81). For patients that were not caucasian, the correlation coefficient was 1.0 and for those without a history of CLP results were 0.92.

In summary, measurement of the Andrews profile analysis during virtual (3D) surgical planning correlated well with traditional methods of measurement through lateral smiling facial photographs.

Posnick JC: Orthognathic Surgery Treatment Planning. Orthognathic Surgery: Principles and Practice 2ed (J. C. Posnick; B.E. Kinard eds) St. Louis Elsevier. Ch. 12, pp. 382-418, 2022.

Resnick CM, Calabrese CE, Resnick AS. Maxillary sagittal position in relation to the forehead: A target for orthognathic surgery. J Craniofac Surg 29: 688-691, 2018