Analysis of Filler Spread: Facial Retinacula Play a Prominent Role

BACKGROUND: Previous ultrasound studies show that unanticipated filler spread can occur during injections. OBJECTIVE: This study investigates filler spread in common facial locations to determine its predictability based on specific anatomical layers. In particular, the authors focused on the direction of filler spread based on the patterns formed by the retinacula superficialis (RS) and retinacula profundus (RP). METHODS: In this observational study, the authors analyzed 440 filler treatments performed on 107 patients by a single injector (primary group) and 22 treatments by 4 additional injectors (reference group). Two filler types were evaluated: (1) 2 volumizing hyaluronic acid fillers and (2) 3 biostimulating fillers. The authors also assessed the feasibility of filler testing at the zygomatic arch. RESULTS: Distinct patterns of filler spread varied by injection site, consistent across both groups. The directional spread was predictable and influenced by the fibrous structures of the RS and RP. In addition, the lengths of the injected bolus varied significantly between the different fillers. CONCLUSION: In uncompromised tissue, filler spread is confined to the injected tissue layer, but follows directions dictated by the RS and RP fibers. While the overall direction of spread is unaffected by filler rheology, the injected length is influenced by the type of filler used.