Glabellar Contraction Patterns and Neurotoxin Efficacy

Background: 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. Methods: 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. Results: 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). Conclusion: 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.