Evaluation of the Midface by Statistical Shape Modeling

Probing real-world Central European population midfacial skeleton symmetry for maxillofacial surgery

OBJECTIVES

Symmetry is essential for computer-aided surgical (CAS) procedures in oral and maxillofacial surgery (OMFS). A critical step for successful CAS is mirroring the unaffected side to create a template for the virtual reconstruction of the injured anatomical structure. The aim was to identify specific anatomical landmarks of the midfacial skeleton, to evaluate the symmetry in a group of the real-world Central European population, and to use these landmarks to assess midfacial symmetry in CT scans.

MATERIAL AND METHODS

The retrospective cross-sectional study defined landmarks of the midface's bony contour using viscerocranial CT data. The distances of the skeletal landmarks (e.g., the frontozygomatic suture and temporozygomatic suture) of the left and right sides from the midline were measured and statistically compared. Midfacial symmetry for reference points was defined as a difference within 0 mm and their mean difference plus one standard deviation.

RESULTS

We examined a total of 101 CT scans. 75% of our population shows symmetrical proportions of the midface. The means of the differences for the left and right sides ranged from 0.8 to 1.3 mm, averaging 1.1 ± 0.2 mm for all skeletal landmarks. The standard deviations ranged from 0.6 to 1.4 mm, with a computed mean of 0.9 ± 0.3 mm.

CONCLUSION

We established a methodology to assess the symmetry of the bony midface. If the determined differences were equal to or lower than 2.5 mm in the mentioned midfacial skeletal landmarks, then the symmetry of the bony midface was considered present, and symmetry-based methods for CAS procedures are applicable.

CLINICAL RELEVANCE

Many CAS procedures require facial symmetry. We provide an easy-to-apply method to probe for symmetry of the midface. The method may be used for population-based research, to check for proper reduction of fractures after reposition or to screen for symmetry prior to CAS planning.

Risk Factors for Maxillary Sinus Pathology after Surgery for Midfacial Fracture: A Multivariate Analysis

This study aimed to determine the incidence of maxillary sinus pathology in patients with a midfacial fracture who underwent osteosynthesis surgery and evaluate the associated risk factors. We conducted a retrospective case-control analysis of patients with midfacial fractures involving a maxillary sinus wall who were treated with open reduction and internal fixation (ORIF) between January 2015 and December 2020. Fracture reduction, the number of screws implanted in the maxillary sinus, and the number of screws penetrating the maxillary sinus, etc., were examined as potential risk factors. Maxillary sinus pathology on postoperative CT was considered the primary outcome for case-control analysis. Binary logistic regression was used to identify variables associated with postoperative maxillary sinus pathology. Thereafter, propensity score matching (PSM) was used to extract confounding factors. A total of 262 patients (totaling 372 maxillary sinuses) were included for analysis. PSM yielded 178, 246, and 70 matched sinuses, respectively, depending on the potential risk factors. Postoperative maxillary sinus pathology was visualized in 218 of the 372 maxillary sinuses (58.60%). The risk factors for postoperative maxillary sinus pathology included the number of screws penetrating the maxillary sinus (odds ratio (OR), 1.124; p = 0.007), an imperfect maxillary sinus wall fracture reduction (OR, 2.901; p = 0.021), and the number of sinus walls involved (OR, 1.383; p = 0.011). After PSM, postoperative maxillary sinus pathology was still more prevalent in sinuses with multiple maxillary sinus wall fractures (64.04% vs. 48.31%, p = 0.034), sinuses with more screws penetrating the maxillary sinus (64.23% vs. 50.41%, p = 0.028), and sinuses with an imperfect reduction (80% vs. 51.43%, p = 0.012). In conclusion, maxillary sinus pathology is common after the ORIF of midfacial fractures. Patients with a fracture of multiple maxillary sinus walls require a close follow-up. Screw penetration of the maxillary sinus should be avoided to prevent maxillary sinus pathology after a midfacial fracture ORIF.

Virtual reconstruction of midfacial bone defect based on generative adversarial network

BACKGROUND

The study aims to evaluate the accuracy of the generative adversarial networks (GAN) for reconstructing bony midfacial defects.

METHODS

According to anatomy, the bony midface was divided into five subunit structural regions and artificial defects are manually created on the corresponding CT images. GAN is trained to reconstruct artificial defects to their previous normal shape and tested. The clinical defects are reconstructed by the trained GAN, where the midspan defects were used for qualitative evaluation and the unilateral defects were used for quantitative evaluation. The cosine similarity and the mean error are used to evaluate the accuracy of reconstruction. The Mann-Whitney U test is used to detect whether reconstruction errors were consistent in artificial and unilateral clinical defects.

RESULTS

This study included 518 normal CT data, with 415 in training set and 103 in testing set, and 17 real patient data, with 2 midspan defects and 15 unilateral defects. Reconstruction of midspan clinical defects assessed by experts is acceptable. The cosine similarity in the reconstruction of artificial defects and unilateral clinical defects is 0.97 ± 0.01 and 0.96 ± 0.01, P = 0.695. The mean error in the reconstruction of artificial defects and unilateral clinical defects is 0.59 ± 0.31 mm and 0.48 ± 0.08 mm, P = 0.09.

CONCLUSION

GAN-based virtual reconstruction technology has reached a high accuracy in testing set, and statistical tests suggest that it can achieve similar results in real patient data. This study has preliminarily solved the problem of bony midfacial defect without reference.

3-D cephalometry of the the orbit regarding endocrine orbitopathy, exophthalmos, and sex

Purpose

This study aimed at evaluating the orbital anatomy of patients concerning the relevance of orbital anatomy in the etiology of EO (endocrine orbitopathy) and exophthalmos utilizing a novel approach regarding three-dimensional measurements. Furthermore, sexual dimorphism in orbital anatomy was analyzed.

Methods

Orbital anatomy of 123 Caucasian patients (52 with EO, 71 without EO) was examined using computed tomographic data and FAT software for 3-D cephalometry. Using 56 anatomical landmarks, 20 angles and 155 distances were measured. MEDAS software was used for performing connected and unconnected t-tests and Spearman´s rank correlation test to evaluate interrelations and differences.

Results

Orbital anatomy was highly symmetrical with a mean side difference of 0.3 mm for distances and 0.6° for angles. There was a small albeit statistically significant difference in 13 out of 155 distances in women and 1 in men concerning patients with and without EO. Two out of 12 angles showed a statistically significant difference between female patients with and without EO. Regarding sex, statistically significant differences occurred in 39 distances, orbit volume, orbit surface, and 2 angles. On average, measurements were larger in men. Concerning globe position within the orbit, larger distances to the orbital apex correlated with larger orbital dimensions whereas the sagittal position of the orbital rim defined Hertel values.

Conclusion

In this study, little difference in orbital anatomy between patients with and without EO was found. Concerning sex, orbital anatomy differed significantly with men presenting larger orbital dimensions. Regarding clinically measured exophthalmos, orbital aperture anatomy is an important factor which has to be considered in distinguishing between true exophthalmos with a larger distance between globe and orbital apex and pseudoexophthalmos were only the orbital rim is retruded. Thus, orbital anatomy may influence therapy regarding timing and surgical procedures as it affects exophthalmos.