Describing the mandible in patients with craniofacial microsomia based on principal component analysis and thin plate spline video analysis.

Craniofacial microsomia (CFM) is most often described as a unilateral malformation of derivatives of the first and second branchial arches. The mandible has been classified using several classification systems. However, all are based on two-dimensional imaging. The aim of this study was to mathematically describe the deformed mandible based on principal component analysis (PCA) in a three-dimensional way. This may aid in defining the flaws in existing surgical corrections of the mandible through the identification of the differences in shape compared with a normal mandible in a holistic view with the help of videos. Forty-three homologous landmarks were defined to describe a mandible with CFM. Computed tomography scans of 22 patients and 30 controls were marked manually. The changes in shape between the mandibles were visualized using videos. A lateral rotation with increase in posterior rotation of the condyle due to shortening of the condyle-gonial height and a longitudinal rotation with outward bending of the mandibular angle were noted on the affected side, as well as an inward bending of the angle on the unaffected side. Due to the compensatory remodelling of the mandible on the unaffected side, one could suggest that CFM is never truly unilateral.