title: The assessment of distorted facial muscles movements in facial palsy
Creators: name: Alagha, Mahmoud Amir M. Mounzer
Publisher: name: University of Glasgow
Year: 2021

description: Introduction The clinical evaluation of facial palsy remains the routine approach for the assessment of facial muscle movements. However, there is a lack of data to link the mathematical analysis of 3D dynamic facial morphology with the subjective clinical assessments. Quantifying the degree of distortion of facial expressions is a vital step in evaluating the clinical impact of facial palsy. 4D imaging is a reliable modality for recording the dynamics of facial expressions. This study aimed to assess distorted facial muscles movements in unilateral facial palsy and mathematically validate clinical grading indices. Material &amp; Method The study recruited 50 patients who suffered from unilateral facial palsy and a control group of an equal number (50) of age- and sex-matched cases. The dynamics of facial expressions were captured using a stereophotogrammetric 4D imaging system. Six facial expressions were recorded (rest, maximum smile, cheek puff, lip purse, eyebrow-raising, eye closure), each one took 4 seconds and generated about 240 3D images for analysis. An advanced geometric morphometric approach using Dense Surface Models was applied for the mathematical quantification of the 3D facial dysmorphology over time. The asymmetries of 10 facial anatomical regions were calculated. For each participant, six mathematical values which quantify asymmetry were measured per expression (the minimal, mean, median, maximum, range, and standard deviation). The 4D image data of sixteen facial paralysis patients were assessed by 7 expert assessors using two clinical grading indices for the assessment of unilateral facial palsy, the modified Sunnybrook index, and the Glasgow Index. The reproducibility of the clinical gradings between two rating sessions was examined. The measured asymmetries of the 4D images were treated as the gold standard to evaluate the performance of the subjective grading indices. Cross-correlations between the mathematical measurements and the subjective grades were calculated. The Modified Sunnybrook index assessed 8 parameters (3 at rest and 5 at individual facial expression). The Glasgow index assessed 29 parameters for the assessment of dynamic facial abnormalities with considerations for the directionality and severity of asymmetry. The similarities and dissimilarities between the two clinical assessments and to the mathematical measurements were investigated. Results The modified Sunnybrook index was reproducible for grading the dysmorphology and dysfunction of unilateral facial paralysis. The Glasgow Index was reproducible after excluding three parameters of poor reproducibility. The modified Sunnybrook index and the Glasgow index correlated reasonably well with the mathematical measurements of facial asymmetry at rest and with facial expressions. • The minimal value of facial asymmetries of the rest expression had a stronger correlation coefficient than that of other values. • The mean and median values of facial asymmetries of the other five nonverbal expressions had a stronger correlation coefficient than that of other values. The following were the main regions affected by facial dysmorphology which showed a correlation above -0.6 between the subjective and objective assessments: • The full face at rest as well as the forehead, cheek, nose and nasolabial, upper lip, corner of the mouth, and chin regions. • The full face, cheek, nasolabial, upper lip, and lower lip of the smile. • The full face, upper and lower lips of the lip purse. • Most of the facial regions, except the cheek, showed moderate to weak correlations with cheek puff. • A strong correlation was detected between the subjective and objective assessments of the forehead and eye regions with eye closure. Based on the correlation results between the mathematical measurements and clinical evaluation of facial asymmetry in unilateral facial paralysis, the study highlighted the following points: • Smile expression: the assessors encountered difficulties to judge the direction of the asymmetry of the corner of the mouth. It is easier to observe the upper lip and the cheek instead of the corner of the mouth when assessing the smile. • Lip purse: the evaluation of the directionality of lip movement was more accurate and sensitive at the lower lip. • Cheek puff: grading the cheek may not grasp the severity of the asymmetry. We would suggest observing the corner of the mouth and lower lip in cheek puff expressions. • Eyebrow raising expression: grading the 4D movement of the upper margin of the eyebrow may be more sensitive than depending on the assessment of the wrinkles of the forehead. • Eye closure: the clinical assessment of the eyes based on 4D image data was not ideal due to the 4D imaging surface defects secondary to the reflective surface of the cornea. Conclusion The mathematical assessment of the dynamics of facial expressions in unilateral facial palsy using advanced geometric morphometrics provides a state-of-art approach for the quantification and visualization of facial dysmorphology. The Glasgow Index and the Modified Sunnybrook Index were reproducible. The clinical assessors were reasonably consistent in the grading of facial palsy. The significant correlations between the clinical grading of facial palsy and the mathematical calculation of the same facial muscle movements provided satisfactory evidence of objectivity to the clinical assessments. The Glasgow index provided more validated parameters for the assessment of facial palsy in comparison to the modified Sunnybrook index. The mathematical quantification of the 3D facial dysmorphology and the associated dynamic asymmetry provides invaluable information to complement the clinical assessments. This is particularly important for the assessment of regional asymmetries and the directionality of the asymmetry for the evaluation of facial contour (anteroposterior direction), face drooping (vertical direction), especially in cases where surgical rehabilitation is indicated.