Topographical characterization of the midfacial musculature revealed by means of high-density surface electromyography
InstitutionsUKU. Klinik für Kieferorthopädie und Orthodontie
UKU. Klinik für Neurologie
This study’s aim was to obtain topographical information of the midfacial musculature and systematically characterize it on a motor unit (MU) level. By means of high density surface electromyography (HDsEMG), motor units’ endplate positions and fiber orientations were examined. Sixteen specially trained, healthy subjects performed selective contraction of midfacial muscles (buccinator (BUC), incisivus (INC), levator anguli oris (LAO), levator labii superioris (LLS), orbicularis oculi (OOC), orbicularis oris pars tangentialis (OOR tan), orbicularis oris pars tangentialis and peripheralis (OOR tan+per), orbicularis oris pars tangentialis and peripheralis and marginalis (OOR tan+per+mar), zygomaticus major (ZYGmaj) and zygomaticus minor (ZYGmin) muscle). Signals were recorded using high-density surface electromyography grids (245 channels). The raw surface electromyography data was decomposed into contributions of single motor units by application of convolution kernel compensation method (CKC). Analysis of decomposed motor unit action potentials (MUAPs) revealed the motor units’ endplate locations and fiber orientations. The results were illustrated in a mean face, which was created by averaging 3D face scan data. A total of 957 MUs were found and assigned to the muscles deliberately contracted during measurement and to levator labii superioris alaeque nasi muscle (LLSan) and nasalis muscle (NAS), which could be distinguished in the analysis as well. OOC and OORmar showed widely distributed endplates on the muscle. A clustering of endplates within individuals but with great variation of the location of clusters between individuals was found for BUC LAO, OORper, OORtan and ZYGmin. A clustering of endplates with similar cluster locations among individuals was found for INC, LLS, LLSan and ZYGmaj. The MUs’ muscle fiber orientations generally conform well to descriptions and drawings in anatomical textbooks and literature. This study’s results contribute to basic anatomical and neurophysiologic knowledge of the facial musculature and may contribute to establish objective electrode placement guidelines or to advance examination methods and (non-)surgical therapies.
Subject HeadingsGesichtsmuskel [GND]
Facial muscles [MeSH]