Automatic measurement of nonparticipatory stiffness in the perioral complex

Purpose: To detail a novel automated technology developed in the authors' laboratory to quantitatively and noninvasively measure perioral passive stiffness in order to consider the feasibility of future applications in patients with facial movement disorders. Method: A stiffness measurement system was developed, with corresponding data sampled from a group of 8 healthy women. Perioral electromyograms were sampled to confirm nonparticipation. A specially designed linear motor servo operating under position feedback was programmed to impose sequential step displacements of the lip at the oral angles over a span of approximately 24 mm. Real-time data acquisition and analysis of resultant force and displacement provide a quantitative, rapid, index of muscle rigidity (stiffness) during a do-not-contract condition. Results: Nonlinear regression techniques revealed that the relation between perioral stiffness and imposed displacement was highly significant. Conclusion: Given the probable relation between certain forms of neuromotor disease and facial rigidity, effects of bomb blast or missile injury on orofacial function, or stiffness changes due to tissue scarring after lip revision surgeries in children with clefts, it is likely that inclusion of facial stiffness measurements will be useful in the management of facial movement disorders.