Mathematical Validation of the Modified Sunnybrook Facial Grading System Using Four-dimensional Imaging

Area of Science:

• Medical Imaging and Biomechanics
• Facial Reanimation and Plastic Surgery

Background:

• The Sunnybrook facial grading system is widely used for evaluating facial palsy, despite known limitations in its validity.
• Dynamic facial asymmetry in unilateral facial palsy requires objective and reproducible assessment methods.

Purpose of the Study:

• To modify and mathematically validate the Sunnybrook facial grading system for assessing dynamic asymmetry in unilateral facial palsy.
• To compare objective, mathematically derived measurements of facial asymmetry with subjective clinical grades.

Main Methods:

• A modified Sunnybrook facial grading system was developed with enhanced descriptive parameters.
• Three-dimensional video analysis and advanced geometric morphometrics quantified facial asymmetry in 16 patients and controls across six expressions.
• Seven assessors graded facial asymmetry using the modified index, with inter- and intra-observer reliability assessed.

Main Results:

• The modified Sunnybrook index demonstrated high inter- and intra-observer reproducibility (r = -0.8).
• Significant positive correlations were found between clinical grades and mathematical measurements for rest, maximum smile, lip purse, and eyebrow raising.
• Correlations were poor for cheek puff and forceful eye closure expressions.

Conclusions:

• The modified Sunnybrook grading index is a reproducible and mathematically valid tool for assessing unilateral facial paralysis in most expressions.
• The system's utility is limited for grading cheek puff and forceful eye closure due to poor correlation with objective measures.