IADR Abstract Archives
Surgical Landmarking and Course of the Masseteric Nerves: A 3D Study
Objectives: Irreversible facial paralysis typically results in significant functional impairment and disfigurement. The masseteric nerves(MN) play an important role in facial paralysis treatment, the proximal segment being used for anastomosis to free transplanted muscle and the distal segment harvested within the hemimasseteric flap. Despite its clinical importance, there are few studies on the intramuscular MN. Our aim was to investigate the extramuscular and intramuscular innervation of masseter throughout its volume using in-situ digitization and 3D modeling.
Methods: Eight formalin-embalmed cadaveric specimens(M6/F2, mean age 84.9±12.2years) were used. V3 was exposed at foramen ovale, MN identified and their extramuscular course digitized at 1-2mm intervals using a Microscribe™ digitzer. Next, the muscle volume and each intramuscular branch, with its arborization, was digitized until it could no longer be seen with a dissection microscope. Data were reconstructed into 3D models in Autodesk® Maya® and the intra- and extramuscular course of the MN documented and compared between specimens.
Results: The extramuscular innervation was received from 2 MN(n=4) or 3 MN(n=4). The most posterior MN entry point was 30.1±3.0mm anterior to mid-tragus, 10.8±1.8mm inferior to zygomatic arch, and 7.7±2.1mm anterior to posterior border of masseter. The intramuscular innervation consisted of 1 main branch coursing infero-anteriorly between the deep(DH) and superficial(SH) heads, and continued intramuscularly in SH. DH was supplied by the main branch and 1-2 secondary branches. The posterior 1/3 and supero-anterior 2/3’s were supplied by 1-2 branches and 2-3 branches, respectively, from the main nerve lying between DH and SH. The main nerve continued intramuscularly in SH to arborize and supply the infero-anterior 2/3’s.
Conclusions: Comprehensive mapping of the masseter innervation in 3D reveals a specific distribution pattern within the muscle. The results provide a basis for further surgical cadaveric studies of MN localization, and for surgical dissection during harvesting for anastomosis or in the design of hemimasseteric flaps.
Methods: Eight formalin-embalmed cadaveric specimens(M6/F2, mean age 84.9±12.2years) were used. V3 was exposed at foramen ovale, MN identified and their extramuscular course digitized at 1-2mm intervals using a Microscribe™ digitzer. Next, the muscle volume and each intramuscular branch, with its arborization, was digitized until it could no longer be seen with a dissection microscope. Data were reconstructed into 3D models in Autodesk® Maya® and the intra- and extramuscular course of the MN documented and compared between specimens.
Results: The extramuscular innervation was received from 2 MN(n=4) or 3 MN(n=4). The most posterior MN entry point was 30.1±3.0mm anterior to mid-tragus, 10.8±1.8mm inferior to zygomatic arch, and 7.7±2.1mm anterior to posterior border of masseter. The intramuscular innervation consisted of 1 main branch coursing infero-anteriorly between the deep(DH) and superficial(SH) heads, and continued intramuscularly in SH. DH was supplied by the main branch and 1-2 secondary branches. The posterior 1/3 and supero-anterior 2/3’s were supplied by 1-2 branches and 2-3 branches, respectively, from the main nerve lying between DH and SH. The main nerve continued intramuscularly in SH to arborize and supply the infero-anterior 2/3’s.
Conclusions: Comprehensive mapping of the masseter innervation in 3D reveals a specific distribution pattern within the muscle. The results provide a basis for further surgical cadaveric studies of MN localization, and for surgical dissection during harvesting for anastomosis or in the design of hemimasseteric flaps.