Abstract
The use of hyaluronic acid-based soft tissue fillers has often been reported to modulate
the muscle, that is, to cause myomodulation. To our knowledge, there has been so far
no scientific study investigating the potential of hyaluronic acid-based soft tissue
fillers to modulate or actually alter the function of facial muscles. To further assess
this three-dimensional (3D) surface imaging and electromyography (EMG)-based prospective
study investigated the changes of facial muscle contraction after injection of strategically
placed hyaluronic acid-based soft tissue fillers to assess the actual validity of
the term myomodulation. A total of 13 subjects with a mean age of 37.8 years (12 females,
1 male) were injected according to a predefined injection protocol. Surface EMG and
3D surface imaging were performed prior to the injection and 5 days after the injection.
The results showed no significant change in the strength of the muscles (measured
in μV) after injection of hyaluronic acid-based soft tissue fillers. However, horizontal
and vertical skin displacement upon contraction of the zygomaticus major muscle changed
significantly between baseline and follow-up, with a mean horizontal skin displacement
increase from 3.2 to 4.1 mm. Upon contraction of the depressor anguli oris muscle,
the horizontal skin displacement did not change significantly (2.15 vs. 2.05 mm),
while vertical skin displacement increased significantly from 2.9 to 4.3 mm. The modification
of the surrounding tissue caused an alteration of the vectorial skin displacement
upon contraction of the muscle. A potential explanation could be the increased distance
between the origin and insertion of the muscle due to the material deposition in the
proximity of the relevant facial muscles, leading to a change of contraction vector.
Keywords
myomodulation - soft tissue filler - EMG - 3D imaging
