LAUSR

BACKGROUND In facial palsy (FP) patients synkinesis of the Depressor Anguli Oris muscle (DAO) is a common pathology impairing dynamic and resting facial symmetry. This prospective study utilizes high-resolution ultrasound (HRUS) to evaluate the morphological features of the DAO and to quantify bilateral differences in DAO cross-sectional diameter (CSD) in individuals with unilateral synkinesis. METHODS From June 2020 to May 2021 30 patients (19 women, 11 men) with clinically diagnosed unilateral synkinesis underwent evaluation with HRUS. DAO, CSD was measured bilaterally, 1 cm inferior to the modiolus in both the resting and smiling positions. RESULTS The Sunnybrook Facial Grading System Synkinesis Score was 6.20 ± 2.48 [0 - 10]. DAO CSD at rest measured 2.41 ± 0.67 mm [1.40 - 4.00 mm] on the control side and 2.66 ± 0.98 mm [1.60 - 5.10 mm] on the affected side, respectively. The DAO on the control side, CSD reduced by - 0.19 ± 0.43 mm [-1.10 - 1.12 mm] when smiling. In contrast, the synkinetic DAO CSD increased by 0.64 ± 0.38 mm [0.00 - 1.59 mm] (p< 0.001) with animation.The pattern of increased CSD in synkinetic DAO muscles and decreased or unchanged CSD on the control side when smiling was identified in 70% of patients. CONCLUSIONS High resolution ultrasound demonstrates increased CSD in synkinetic DAO muscles during active smiling. The opposite is true for DAO muscles on the control side that exhibit decreased CSD with animation. HRUS may be performed preoperatively to objectify DAO dysfunction and guide targeted therapy.