Geometric Morphometric Analysis of Forehead Morphology in Unicoronal Synostosis: Identifying the Pivot Line

Unicoronal synostosis (UCS) causes asymmetric forehead morphology and is commonly managed with fronto-orbital advancement (FOA). However, optimal reconstruction remains challenging as the location of the forehead's pivot line, the hinge axis for advancement, often remains uncertain. We conducted a geometric morphometric analysis using 235 cranial landmarks in 16 patients with UCS (aged <2 y) and 11 age-matched controls. CT-derived cranial models were assessed with generalized Procrustes analysis and principal component analysis (PCA) to evaluate morphologic asymmetry and identify potential pivot lines. PC1 (35.7%) captured asymmetric differences, whereas PC2 (22.8%) represented symmetric variation. Compared with controls, patients with UCS exhibited frontal retrusion and temporal bossing on the affected side, along with frontal bossing on the contralateral side. Wireframe deformation revealed morphologic deviation concentrated near the orbit but not along the cranial midline. Importantly, pivot lines differed between the frontal bone and the supraorbital bandeau, suggesting independent hinge axes. In UCS, the pivot line is not at the midline but lateralized near the orbit. Consequently, the frontal bone and supraorbital bandeau should be repositioned around a separate hinge axis during FOA. These findings support more symmetric and individualized cranial reconstruction.