Quantitative Analysis of Facial Motion Components: Anatomic and Nonanatomic Motion in Normal Persons and in Patients with Complete Facial Paralysis

The maximal static response assay of facial motion, described in 1994, enables the simultaneous measurement of multiple facial motions by tracking the positions of specific facial points. While the maximal static response assay provides accurate measurement of facial motion, the analysis of these data lacks the simplicity of a single-number scale such as the House-Brackmann system, a subjective scale traditionally used to classify facial function. The purpose of this study was to develop a simplified numerical index capable of summarizing the data generated by the maximal static response assay in a clinically meaningful way. We also wanted to develop a method whereby only anatomic motion or nonanatomic motion in the paralyzed face could be quantitated. Anatomic motion is the motion of the specific facial points studied by the maximal static response assay that can be attributed solely to the pull of the regional facial muscles that govern the movement of those points. Nonanatomic motion is motion that is secondary to the pull of the unaffected contralateral muscles that is transmitted to the paralyzed hemiface. Thirty-four patients with complete facial paralysis were studied. The maximal static response assay was performed on all patients on presentation to the Facial Nerve Center at the University of Pittsburgh Medical Center or after development of complete facial palsy postoperatively. The data from these patients were compared with maximal static response assay data from 26 unaffected controls. The anatomic index of facial motion and the nonanatomic index of facial motion were calculated for all study participants. The anatomic index of facial motion measures anatomic facial motion, and the nonanatomic index of facial motion measures nonanatomic facial motion. To calculate the anatomic index of facial motion, the vector magnitudes of the supraorbital, infraorbital, and modiolar motions during brow lift, eye closure, and smile are summed. The anatomic index of facial motion represents a ratio of this sum on the affected side to the corresponding sum on the unaffected side using only anatomic motions. The nonanatomic index of facial motion is a similar ratio using nonanatomic motion only (i.e., motions in directions that cannot be produced by the ipsilateral muscles). The anatomic index of facial motion represents a single number that can be used to assess facial motion. The value of the anatomic index of facial motion for patients with complete facial paralysis is 0.07 +/- 0.08. The anatomic index of facial motion for normal individuals is 1.05 +/- 0.13 (p < 0.0001, Mann-Whitney rank-sum test). The nonanatomic index of facial motion in normal individuals is 0.05 +/- 0.08; in patients with complete facial paralysis, it is 0.34 +/- 0.32 (p < 0.0001, Mann-Whitney rank-sum test). During recovery from complete facial paralysis, the anatomic index of facial motion and the nonanatomic index of facial motion each revert steadily toward normal values. The anatomic index of facial motion and the nonanatomic index of facial motion are single numbers based on the maximal static response assay, which quantitatively describes anatomic motion and nonanatomic motion in patients with complete facial paralysis. Although patients with complete facial paralysis have motion on the paralyzed hemiface, the motion is primarily nonanatomic. Both indices can be used to track recovery from complete facial paralysis.