Three-Dimensional Motion Capture of a Smile in Repaired Unilateral Cleft Lip: What's Our Vector, Victor?

Introduction: Following surgical repair, patients with unilateral cleft lip (UCL) exhibit dynamic asymmetry during facial expressions compared to healthy individuals. Previous studies using Euclidean distances to describe this asymmetry fail to take the direction of the movement into account. The aim of this study is to compare differences in participants with UCL and controls using analysis of motion vectors during facial expressions.

Methods: In this cross-sectional study, twenty-six pediatric participants were recruited: 13 participants with repaired left UCL and 13 participants with no craniofacial diagnosis. Participants were recorded performing a maximal smile by a 4D stereophotogrammetric system. Phases of the smile were divided into closed lip and open lip smiles. Ten regions of interest were analyzed: subnasal area, upper lip, lower lip, oral commissure, and ala on both sides. The motion vectors were calculated and vector magnitude and direction for each region was compared.

Results: Between cleft and control groups, the differences in vector direction were greater than the magnitude differences. Significant differences in vector direction were identified at both oral commissures in the closed lip smile; and at the oral commissure, subnasal, upper lip, and lower lip regions during open lip smile.

Conclusions: Vector analysis demonstrated significant movement asymmetry during facial animation in participants following UCL repair, not previously identified when analyzing magnitude of skin displacement.