Ultrasound Evaluation of Lip Anatomy and Filler Placement: A Cross-Sectional Study of Injection Accuracy, Migration, and Demographic Variation

BACKGROUND: Lip fillers composed of hyaluronic acid are commonly used for aesthetic enhancement, yet the anatomical changes they induce and their relationship to demographic factors remain incompletely understood. METHODS: A cross-sectional study of 126 participants was conducted at clinics in London and Amsterdam. High-frequency ultrasound was used to assess lip layer thickness, submucosal gland dimensions, and filler position. Demographic data were recorded and correlated with anatomical findings and filler distribution. RESULTS: Treated patients demonstrated significantly increased thickness in the connective tissue and pars peripheralis layers. The subcutaneous layer averaged less than 1 mm in both upper and lower lips, resulting in intramuscular filler placement in most treated individuals. Vertical injection techniques were associated with deeper filler deposition, hypervascularity, and evidence of migration. Lip anatomy varied significantly with sex, race and ethnicity, body mass index, and age. CONCLUSIONS: Hyaluronic acid fillers alter lip anatomy in measurable ways, often resulting in unintended intramuscular placement due to the limited subcutaneous space. Demographic factors significantly influence lip structure and filler behavior, supporting the need for individualized treatment planning. Future studies should investigate long-term outcomes and patient perspectives.