Early degradation is a common complaint for hyaluronic acid fillers. Although the combination of hyaluronic acid fillers with botulinum neurotoxin type A presented improved clinical results, objective measurement of hyaluronic acid volumes has not been previously assessed.
In this study, the authors have split the calvaria of the rabbit to mimic the glabellar region in humans. In this model, the authors applied hyaluronic acid alone to one side and hyaluronic acid combined with botulinum neurotoxin type A to the contralateral side. Two days and 3 months after the filler injection, magnetic resonance imaging was performed to assess the filler volumes.
Average initial volume of filler only and filler combined with botulinum neurotoxin type A was 0.61 cm3 on both sides, and there was no difference between initial volumes of the two sides (p = 0.735). At the end of 3 months, average degraded volumes of filler-only and filler combined with botulinum neurotoxin sides were 0.33 cm3 and 0.19 cm3, respectively, and the degradation difference was significant between the two groups (p = 0.001). End volumes for the filler-only and filler combined with botulinum neurotoxin sides were 0.28 cm3 and 0.42 cm3, respectively, and end volumes between two sides were also statistically significant (p < 0.001).
This study showed that hyaluronic acid filler application in combination with botulinum neurotoxin type A significantly decreases the degradation process and increases the remaining volume of the hyaluronic acid fillers at the end of the paralyzed period.