Ultrasound Guidance for Botulinum Toxin Injection of Muscles Innervated by the Facial Nerve: A Systematic Review of Anatomical Precision, Safety, and Outcomes.

Botulinum toxin type A (BoNT-A) chemodenervation is commonly used for facial synkinesis and aesthetic indications, but landmark-based techniques are limited by anatomical variability and risk of off-target delivery. High-resolution ultrasound (US) can be used to enhance precision and safety. This systematic review explores the role of US-guided BoNT-A facial chemodenervation in evaluating anatomical accuracy, clinical efficacy, complications, and patient satisfaction. A comprehensive search of 6 databases through April 2025 identified studies assessing US-guided BoNT-A chemodenervation for facial indications. Sixteen studies were included, comprising randomized controlled trials, prospective cohorts, cadaveric trials, and anatomical mapping investigations. Data on injection accuracy, clinical outcomes, adverse events, and patient-reported measures were extracted. Risk of bias was assessed using validated tools. US guidance improved injection accuracy, with cadaveric trials demonstrating up to 88% accuracy, whereas landmark-based techniques reported 50%. Clinical studies reported improvements in rhytid reduction, oral commissure elevation, neck relaxation, and facial symmetry. Adverse events were infrequent and mild. Patient satisfaction was consistently higher with US guidance. Anatomical studies identified muscle depth variation and vascular risk zones, supporting real-time sonographic targeting. As a result, the authors found that US-guided BoNT-A chemodenervation improves the safety, precision, and outcomes and should be considered in both therapeutic and aesthetic applications. Level of Evidence: 3 (Therapeutic).