Filler Injection Techniques and Ultrasound Observations: Ultrasound-Based Classification of Volume Deficiency in Nasolabial Folds.

Background: Nasolabial folds (NLFs) are a hallmark of facial ageing, and precise correction requires detailed anatomical and vascular mapping. High-resolution ultrasound offers real-time visualisation of soft-tissue layers, filler distribution, and vascular anatomy, enabling safer and more targeted injection. This study integrates ultrasound into the aetiologic classification and treatment algorithm for NLF correction in Korean patients, whose facial artery course and subcutaneous fat distribution differ subtly from Western populations.

Methods: Fresh cadaver dissections were correlated with ultrasound imaging in 45 Korean patients presenting for NLF correction. NLFs were categorised into three aetiologic types-(1) volume deficiency, (2) tissue laxity, and (3) muscular tethering-based on both clinical and ultrasound assessment. Volume-deficient folds were treated with biphasic hyaluronic acid filler using a deep-then-superficial layering approach under ultrasound guidance, with real-time confirmation of injection depth and avoidance of vascular structures. Injection techniques included needle and cannula methods (Fern-leaf, Duck-walk) and hyaluronic acid filler (Lorient No 6 and 4, Joonghun Pharmaceutical) has been used. Global Aesthetic Improvement Scale (GAIS) scores and adverse events were recorded over 12 weeks.

Results: Ultrasound allowed precise differentiation of superficial and deep fat loss patterns and identified individual variations in facial artery course in 38% of patients. Of the 45 patients, 20 (44%) had volume-deficient NLFs and underwent ultrasound-guided filler placement. GAIS improved from baseline "no change" (0) to a median "much improved" (2) at 12 weeks, with no vascular compromise or filler malposition observed. Ultrasound also detected early filler integration and confirmed even distribution in targeted planes. Patients with laxity- or muscle-dominant folds, identified by ultrasound, benefitted from adjunct thread lifting or low-dose botulinum toxin.

Conclusions: Ultrasound-guided, anatomy-based filler injection offers enhanced safety, precise plane targeting, and real-time monitoring of filler distribution in NLF correction. Integrating ultrasound into aetiologic classification improves treatment planning and reduces complications, particularly in populations with variable vascular anatomy. Larger controlled trials are recommended to validate long-term outcomes.

Level of evidence v: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .