Finite Element Analysis Of Biomechanics Of Injured Levator Ani Muscle In Female Patients With Moderate To Severe SUI

Objective:Based on the MRI image datas of pelvic floor and the method of reverse engineering,to establish a three-dimensional finite element model of injured levator ani muscle in female patients with stress urinary incontinence(SUI),and then to simulate the displacement and stress distribution of the injured levator ani muscle under abdominal pressure,observe the location of the maximum displacement and stress by means of finite element analysis method,aiming to explore the mechanism of occurrence and development of stress urinary incontinence in women further from a mechanical point of view and provide the basis of biomechanical theory for the improvement of pelvic floor repair treatment.Methods:The 3.0T nuclear magnetic resonance scanner(GE Siganl 3.0T magnetic resonance machine)was used to scan pelvic tissue of women with moderate to severe SUI in our department.The patient took a conventional supine position and performed a cross-sectional magnetic resonance scan since the middle of the bladder to the external vaginal opening.The layer thickness was 2.0 mm.Collected the raw datas of pelvic MRI images.Selected 1 case of female patients with moderate to severe SUI with injured levator ani muscle by reviewing the images.Import the original magnetic resonance datas into MIMICS 19.0 medical image three-dimensional reconstruction software in DICOM(Digital Imaging and Communications in Medicine)format to construct a three-dimensional geometric model including pelvis,injured levator ani muscle and bilateral obturator muscles.Optimized the geometric model by means of reverseengineering technology.Then imported the optimized model into ANSYS 18.0 finite element analysis software,and the finite element model was generated after defining the element type,endowing material attributes and meshing volume.The actual measured urodynamic results were applied as necessary loads.Obtained the displacement and Von Mises stress distribution nephogram of injured levator ani muscle.Observed the displacement and Von Mises stress distribution characteristics of injured levator ani muscle,and the location of maximum displacement and Von Mises stress.Results:1.The three-dimensional finite element model of injured levator ani muscle in female patients with moderate to severe SUI was established successfully based on the pelvic floor MRI image datas and reverse engineering method.2.The displacement and Von Mises stress nephograms of the model under three states and six working conditions were obtained and the maximum displacement(mm)and the maximum Von Mises stress(Mpa)were calculated.3.The displacement and Von Mises stress nephogram of the model under three states and six working conditions were asymmetrically distributed on the left and right.The maximum displacement occurred at the location of the tear in the levator ani muscle,and the maximal Von Mises stress occurred at the joint of levator ani muscle and sacrum and near the rupture side.4.The maximum displacement and Von Mises stress of the injured levator ani muscle shown in this model increase with the increase of the load on the levator ani muscle surface under the same condition(i.e.the elastic modulus of the muscle is constant).In the same position,abdominal pressure increases with the increase of elastic modulus of muscle,and the maximum displacement and Von Mises stress also increased correspondingly.Conclusion:The three-dimensional finite element model of the injured levator ani muscle based on pelvic floor thin-slice scanning datas is authentic and dependable,and it can reflect the spatial and three-dimensional anatomical relationship of pelvic floor.Based on the finite element stress analysis method and the corresponding urodynamic inspection results of the same patient,the regularities of distribution of displacement and stress of the injured levator ani muscle in female patients with moderate to severe SUI can be more accurately reflected.The transmission of abdominal pressure along the pubic visceral muscles was interrupted after the levator ani muscle was injured.Under the action of abdominal pressure,the forces on both sides of levator ani muscle were uneven,and the ability of the levator ani muscle to carry abdominal pressure also decreased.From the mechanical point of view,the loss of stability of pelvic floor support structures may be one of the causes of SUI,which also provide a certain theoretical basis of biomechanics for the improvement of pelvic floor repair and treatment technology.