Stiffness: a pathophysiologic approach to diagnosis and treatment

Nonparticipatory stiffness in the male perioral complex

PURPOSE

The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults.

METHOD

Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a computer-controlled linear servo motor to impose a series of tensile displacements over a span of approximately 24 mm at the oral angle in 20 healthy young male adults. Perioral electromyograms were simultaneously sampled to confirm nonparticipation or passive muscle state. Perioral stiffness, derived as a quotient from resultant force (DeltaF) and oral span (DeltaX), was modeled with regression techniques and subsequently compared to previously reported perioral stiffness data for female adults.

RESULTS

Multilevel regression analysis revealed a significant quadratic relation between the perioral stiffness and interangle span; however, no significant difference was found between adult males and females.

CONCLUSION

These normative measures will have application to future studies designed to objectively assess the effects of pathology (i.e., progressive neuromotor disease, traumatic brain insult) and intervention (pharmacologic, neurosurgical, and reconstructive surgery of the face [i.e., cleft lip, trauma, missile injuries]) on facial animation and speech kinematics.

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.