3-Dimension Anatomy And Biomechanical Study Related To Human’s Nasolabial Musculature

Research backgroundOribularis oris and nasalis belong to the muscles of facial expression with complex structure, and can attach to the dermis of the upper and lower lip by the superficial musculoaponeurotic system. They are particularly important because they are related to the lip movements, formation of philtrum and outline of the nostril. We have been familiar with the gross anatomy of orbicularis oris, but further study is still needed for the complex and irregular three-dimensional structure. For plastic surgeons, it is important for them to understand the spatial relationship between the anatomical structures of muscles in nasolabial region and the profile of the region, and the role of nasolabial musculature in the formation of the profile of the nose and lips.Objective1Micro-CT combined with iodine staining technique was adopted to scan the nasolabial tissues of3aborted fetuses. After we obtained the strictly aligned and corrected full-capacity two-dimensional gray-scale image was obtained, the three-dimensional reconstruction software was used to perform a three-dimensional reconstruction of these images (including11normal fetuses and4cleft fetuses).2Based on the3D model of the nasolabial musculature, Catia was used to reconstruct the3D digital model of skin-muscle-cartilage at the nasolabial region. The validation of the model:splitting the upper lip of one side to simulate the formation of unilateral complete cleft lip deformity.3Through the adjustment of tightness and connection among the fibers of nasolabial muscle, the corresponding changes of nose and lip could be noted. It would provide guidance for the operation of the correction of secondary deformities of the cleft lip.Materials and methods 1. Getting the images of sectional imaging anatomy of the normal upper lip: a total of11nasolabial tissues without deformity were ready for scanning. The tissues were properly soaked in4%formalin solution to be fixed for24hours. The specimen to be scanned needed to be immersed in iodine-potassium iodide (I2-KI) solution (Lugol’s Solution) with the concentrations of1.87,3.75,7.5and15%for staining at least for2days. With micro-CT, images with different definition were obtained, and the ones with3.75%Lugol’s iodine staining got the best clarity. All these clear images were saved in DICOM, and were edited in Mimics. After three-dimensional calculation, the3D model of normal nasolabial musculature were got.2. Getting the images of sectional imaging anatomy of the cleft lip:a total of4nasolabial tissues from cleft fetuses were ready for scanning. The tissues were properly soaked in4%formalin solution to be fixed for24hours. The specimen to be scanned needed to be immersed in iodine-potassium iodide (I2-KI) solution (Lugol’s Solution) with the concentrations3.75%for staining for2days.With micro-CT, images the images of sectional imaging anatomy were obtained. All these images were saved in DICOM, and were edited in Mimics. After three-dimensional calculation, the3D model of cleft nasolabial musculature were got.3. Reconstruction of the simplified3D model of normal nasolabial tissues: according to the above virtual3D model and relevant anatomical data, a new solid model with skin, muscle, and cartilage was reconstructed. Then the model was meshprocessed in Hypermeshll.0. The model was meshed with tetrahedral element and beam element. After the grid processing, the data was saved as HM format, and imported into Abaqus for analysis.4Three dimensional finite element analysis:according to previously published papers, linear parameters of muscle and cartilage, and nonlinear constitutive equation of the skin and fibrous connective tissue were obtained. Calculation and analysis are carried out by Abaqus software. Model validation:the formation of unilateral complete cleft lip. Model loading:①connect the end of nasal is alar part and contralateral pars peripheral is, and load1N on the both of the sides;②connect the foot plate of alar cartilage and a bundle fibers of pars peripheralis at the same side, and load1N in the same way;③.①and②were loaded simultaneously.④the columella part of nasal muscle was loaded1N in the same way.Results1.1. The data sets of sectional anatomy with normal fetuses:there are four groups of orbicularis oris muscle fibers in the upper lip area, respectively pars marginalis, pars peripheralis, muscle fibers of levator labii superioris and nasal muscle complex.1.2. The data sets of sectional anatomy with cleft fetuses:①on the normal side of the incomplete unilateral cleft lip,4parts of orbicularis oris muscle still exist:the pars marginalis, pars peripheralis, distal muscle fibers of levator labii superioris alaeque nasi and the and the nasal complex. But they had a bit deformation and displacement compared with the normal upper lips. On the cleft side, the muscle fibers were immature, disorganized and did not gathered into bundles and with no clear direction.②In the bilateral cleft lip, no muscle fibers were found in the soft tissues of the premaxilla. The muscle fibers of the lip tissues in the lateral cleft was chaotic, mixed and with no clear direction, and no obvious muscle bundle.1.3. Verification of the model:the results of the simulation of the formation of the complete unilateral cleft lip were mostly the same with clinical practical.1.4. Simulation of the model:①when the end of nasalis alar part and contralateral pars peripheralis was connected and loaded, the nose tip turned up, the alar sulcus was deepened, the wing of the nose on the both sides moved towards the midline, and the philtrum turned more remarkable;②when the foot plate of alar cartilage and a bundle fibers of pars peripheralis at the same side were connected, the nose tip turned down, the philtrum and philtral ridge bulged,and the width of upper lip narrowed.③when①and②were loaded simultaneously, the alar sulcus was deepened, the wing of the nose on the both sides moved towards the midline, the nose tip turned up, the philtrum and philtral ridge bulged, and the width of upper lip narrowed.④when the columella part of nasal muscle was loaded, the nasal floor bulged and turned more remarkable.Conclusions 1. when the end of nasalis alar part and contralateral pars peripheralis was connected below the nasal floor, a new strip of muscle was formed;When the bundle contracted along the long axis, the alar cartilage rotated cephally; the nasal tip turned more remarkable, the wing of the nose moved inward and the philtrum dimple deepened, philtrum ridge is more remarkable.②when a bundle of fibers of pars peripheralis was sutured to the foot plate of the alar cartilage on the same side, the philtral ridge and philtrum were uplift and the philtrum turned more remarkable;③The integrity of the nasalis columella nasi has to do with formation of the nasal sill, and when the anatomical location of the nasalis columella nasi was restored in operation, the collapsed nasal floor uplift, and the nasal sill recurred.The main innovation points1. It was found that the soft tissue could be enhanced and differentiated with micro-CT after treated with I2KI solution. The muscle fiber, vascular, adipose tissue, and tooth germ could be developed clearly. There’s no report about this technique applied to the soft tissue of human body before, and it could be a complement to current methods of human anatomy research.2It was the first time for us to gain the sectional imaging anatomy of the normal lip and the cleft lip. and the muscle fibers could be clearly demonstrated. It is also of great value for the study of the anatomy of upper lip and embryo development. Besides, it do good to the study of the formation of cleft lip deformation.3It is the first time for us to establish the three-dimensional finite element model of the upper lip containing skin, muscle, and cartilage. The simulation that by changing the tightness and connection of the muscle fibers to alter the lip and nose appearance, provide some guidance for the correction of secondary deformities of the clefts.