[Computerized analysis of normal associated movements of facial mimic muscles]

There have been many reports on the synkinesis of mimic muscles following facial palsy, and many efforts have been made to evaluate the degree of synkinesis. Even in normal cases, associated movements of facial muscles can been seen. Empirically, mimic muscles move in association, e.g., when the lips are opened to grin, the lateral portion of the eyebrow moves, or when the mouth is moved as in whistling, tension around the root of the nose subconsciously builds up. Our purpose was to evaluate the movements of facial mimic muscles quantitatively, to analyze them in various facial expressions, and to obtain basic data to the objective evaluation of associated movement in normal subjects. Thirty-seven normal subjects (18 males and 19 females, aged 20 to 40 years) were included in the study. A total of 24 markers were stuck to each subject's face. The threshold image process which revealed only the markers, made it possible to trace and measure the markers on the face. The shifting positions of the markers showed that they moved in accordance with the facial movement from the stationary phase to the maximum stage of movement. These positions were measured and the traces plotted on the coordinate axis. The shifting of the markers were then numerically expressed as trajectory investigation. The facial movements examined in this study consisted of eye closing, forehead wrinkling, whistling, and grinning. We found that, quantitatively, certain groups of mimic muscles might work together to make one facial expression in all the above mentioned facial movements. In normal individuals, at least 15-20% of other mimic muscle collaboration is needed in addition to main muscles to create a facial expression. This result can serve as a reference for the evaluation of abnormal associated facial movement.