Simultaneous Quantitation of Three-Dimensional Absolute and Relative Displacements in Facial Movements-A Local Face Frame Technique

Abstract

Facial motion analysis has been developed in recent years for quantitative analysis of facial expressions. Usually, the vector of absolute movement of facial markers is evaluated for quantitative analysis, such as two-dimensional evaluations of Johnson. Although it is a practical method, the major problem of measurement of absolute displacement is how to maintain the head of subject in a stationary position during facial expression. Trotman recommends the three-dimensional measurement of inter-landmark separation of paired markers as a complementary method of absolute displacement to solve this problem. In our study, the three-dimensional absolute displacement of paired facial markers was used to compare the relative displacement, with a technique of local face frame to solve the problem of head movement. A motion analysis with an Expert Vision HiRes system was used to quantitatively evaluate five facial expressions: brow lift, eye closure, smile, puffy face, and whistle in thirty subjects. The results reveal that the measurement of absolute displacement in a local face frame is a repeatable, quantifiable, and practical method in clinical application. The relative displacement of paired markers is not suitable in the quantitative analysis of eye closure, whistle, and puffy face, and it also under-estimates the absolute displacement of facial movement in brow lift and smile (P＜0.001). The local face frame technique is recommended to prevent the errors caused by position changes of head during measurements, instead of relying on relative displacement of paired facial markers. Surgeons can use this system of facial motion analysis to objectively evaluate the progression and surgical outcome of patients with facial palsy.