Background: Soft tissue filler injections are performed using either sharp-tip needles or blunt-tip cannulas. Product can change planes in an uncontrolled manner during needle injections, potentially leading to unintentional intra-arterial placement. There is a paucity of data on the influence of injection angle on the dispersion patterns of soft tissue fillers.
Materials and methods: A total of 126 injection procedures were conducted in seven Caucasian body donors (four males, three females) with a mean age of 75.29 ± 4.95 years and a mean body mass index of 23.53 ± 3.96 kg/m2 . Injection procedures were performed in various facial regions (forehead, scalp, zygomatic arch, mandibular angle), utilizing different needle sizes (25G, 27G, 30G) and different angles (90°, 45°, 10°). Layer-by-layer dissections were performed to verify the location of the injected product. Dissections were facilitated by the colored material.
Results: Utilizing a 30G needle (compared to a 25G needle) reduces the superficial spread with OR 0.70 (95% CI, 0.48-0.99) and P = 0.049, whereas injecting at 90° (vs 10° with the bevel down) increases the odds for superficial spread with OR 10.0 (95% CI, 7.11-14.09) and P < 0.001.
Conclusion: Precision during soft tissue filler injections, defined as the product remaining in the plane of intended implantation, can be enhanced by changing the needle size and the injection angle. Utilizing a 30G needle and injecting at a 10° angle with bevel facing down reduces the uncontrolled product distribution into superficial fascial layers.
Keywords: facial anatomy; hyaluronic acid; injections; layers of the face; needles; safety; soft tissue fillers.
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