Glabellar Contraction Patterns and Neurotoxin Efficacy: A Quantitative Assessment.

Abstract

Standard neurotoxin treatment for glabellar frown lines typically uses a fixed 5-point injection technique, despite variability in muscle recruitment patterns among patients. A classification system [U, V, Omega (O), Inverted Omega (IO), Converging Arrows (CA)] describes these variations, but their impact on treatment outcomes has not been quantitatively assessed. This study evaluates how glabellar anatomy influences neurotoxin efficacy using objective 3D strain analysis. A total of 142 women underwent standardized 5-point injections targeting the bilateral corrugator supercilia and procerus muscles. Patients were categorized by the senior author into glabellar patterns based on muscle recruitment: U (procerus, corrugators), V (plus medial orbicularis), O (orbicularis and frontalis), IO (procerus, corrugators, internal orbicularis, nasalis), and CA (balanced procerus/frontalis). Dynamic strain was quantified via Vectra M3 imaging at baseline, 3, 30, 90, and 180 days post-injection. Group differences in baseline strain and treatment outcomes were assessed using 1-way ANOVA. Significant baseline strain differences existed among patterns (P=0.029), with the highest in U (16.54%) and the lowest in IO (12.01%). All patterns showed strain reduction by day 90, but only U and CA remained significantly improved at 180 days (P<0.05). Peak efficacy was observed on day 30. Patterns U, V, and O demonstrated higher residual strain, while IO showed the lowest absolute strain but smallest reduction (8.37%, P=0.002). Glabellar contracture patterns significantly affect baseline activity and duration of neurotoxin efficacy. Patterns O and IO exhibit shorter-lived improvements, suggesting customized injection protocols targeting additional muscles (frontalis, orbicularis, nasalis) may enhance patient outcomes.