A Novel Method for Quantitative Three-Dimensional Analysis of Zygomatico-Maxillary Complex Symmetry

Objective: To develop a reliable and accurate method to quantify the symmetry of the zygomaticomaxillary complex (ZMC). Methods: Virtual three-dimensional models were created from 53 computed-tomography scans: 15 healthy cases without maxillofacial disorders and 38 patients with ZMC fractures requiring surgical treatment. Asymmetry of the ZMC was measured using a mirroring and surface-based matching technique that uses the anterior cranial fossa as reference to determine the symmetrical position of the ZMC. The measure for ZMC asymmetry was defined as mean surface distance (MSD) between the ZMC-surface and the symmetrical position. Reliability of the method was tested in the 15 healthy cases. Inter-and intra-observer correlation coefficients (Ce) and variabilities were assessed. Accuracy was assessed by comparing ZMC asymmetry between healthy and ZMC fracture cases, and by assessing correlation of ZMC fracture severity with ZMC asymmetry. Results: The average MSD of the 15 healthy cases was 1.40 ± 0.54 mm and the average MSD of the 38 ZMC fracture cases was 2.69 ± 0.95 mm (P < 0.01). Zygomaticomaxillary complex asymmetry correlated with fracture severity (P = 0.01). Intra-rater CC was 0.97 with an intra-rater variability of 0.09 ± 0.11 mm. Inter-rater Ce was 0.95 with an inter-rater variability of 0.12 ± 0.13 mm. Conclusions: Our method is reliable and accurate for quantitative three-dimensional analysis of ZMC-symmetry. It takes into account asymmetry caused by the shape of the ZMC as well as asymmetry caused by the position of the ZMC. Clinical relevance: This method is useful for the evaluation of ZMC asymmetry associated with congenital and acquired disorders of craniofacial skeleton, for surgical planning and for evaluation of postoperative results.