Computer Simulation Biomechanical Study Based On Magnetic Resonance Imaging Of Female Pelvic Organ Prolapse

Objective(s):1.A method of quantifying and measuring the shape and position of uterus and vagina was proposed.Magnetic resonance imaging was used to verify the differences in the axis,length and position of uterus and vagina between prolapsed women and non-prolapsed women,and to study the role of uterine-vaginal mechanics in pelvic floor support.to provide theoretical support for the evaluation of pelvic floor function and the improvement of the pathogenesis of pelvic floor functional disorders.2.In view of the complex relationship between structure and biomechanics of female pelvic floor support system,a fine geometric model of sagittal pelvic floor was constructed by two-dimensional equivalent mechanics method.to explore the influence of the shape and position of pelvic floor organs and tissues on the biomechanical properties of pelvic floor under different abdominal pressure,in order to reveal the mechanical mechanism of pelvic floor stress injury.3.On the basis of the previously developed two-dimensional refined equivalent mechanical model of pelvic floor based on anatomy,the two-dimensional structural model was further optimized to analyze the strain and stress of pelvic floor tissue.The stress and strain characteristics of pelvic organs in pelvic support system under abdominal pressure load of different physiological states were discussed.The method of fitting the constant parameters of superelastic material was used to simulate the damage state of the main supporting structure of pelvic floor.The effects of injury of main ligament,hysterosacral ligament,levator anus muscle and anterior vaginal wall on the mechanical properties of pelvic floor tissue were analyzed,and the formation mechanism of anterior vaginal wall prolapse caused by anterior vaginal wall injury was simulated.4.Through the establishment of three-dimensional anatomical model and three-dimensional finite element biomechanical analysis model of pelvic support system in patients with pelvic organ prolapse and non-prolapse subjects,to explore the stress and strain characteristics of pelvic organs and supporting structures of pelvic floor under different physiological conditions of abdominal pressure,and to analyze the effect of pelvic organ morphological changes on pelvic floor tissue mechanical support in pelvic organ prolapse and non-prolapse subjects.Evaluation of the biomechanical relationship between individual anatomical structures and combinations of pelvic organ prolapse and non-prolapse subjects.Methods:1.Through the analysis of the MRI image data of 81 prolapsed women and 57 non-prolapsed women,the length and angle of the superior,middle and inferior axes of the uterine body,cervix and vagina,and the angle relative to the pelvic tilt correction system were compared,and the standard coordinate system was established in the sagittal position with the subpubic point of the pelvis and the sacral promontory mark as the reference frame.The coordinate parameters of important anatomical sites of uterus and vagina were measured and their positions were analyzed and described.2.By using the method of MRI two-dimensional image analysis and computer aided design,a two-dimensional finite element model is constructed on the basis of accurately reconstructing the geometric model of female pelvic floor support system,and the biomechanical characteristics such as stress distribution,shape and position changes of pelvic floor organs under different abdominal pressure loads are analyzed.3.Based on the median sagittal MRI images of a healthy woman with average pelvic floor size,a new two-dimensional finite element biomechanical model of pelvic floor based on image anatomy is constructed on the basis of previous studies.In this model,all variable structures are defined as isotropic nonlinear hyperelastic materials under different damage combinations of supporting structures and abdominal pressure loads of different physiological states.The stress-strain characteristics and mutual support of the supporting structure of the pelvic floor are analyzed.Then,according to the different combinations of tissue injury of main ligament and uterine-sacral ligament complex,levator anus muscle and anterior wall of vagina,the injury was simulated by reducing the mechanical properties of each supporting structure.the computer numerical simulation method was used to predict the mechanical action and morphological changes of healthy and damaged tissues in different states.4.Dynamic magnetic resonance imaging was performed on a healthy female volunteer and a patient with prolapse to establish three-dimensional models of pelvis,bladder-urethra,uterus-vagina,rectum,levator anus,perineal body,main and hysterosacral ligamenta.The three-dimensional spatial structure was anatomically compared and analyzed,and a three-dimensional biomechanical finite element model specific to the object was further established.Six different physiological conditions of abdominal pressure were simulated to analyze the stress and deformation of bladder,urethra,uterus,vagina,rectum,levator anus,perineal body,main and uterine sacral ligament under different stress conditions.simulate the stress and deformation of pelvic floor supporting structure and tissue organs with the increase of intra-abdominal pressure,so as to provide theoretical support for the interaction between pelvic floor supporting structure and tissue organs under different intra-abdominal pressure.Results:1.The uterine body-cervical angle and cervical-the upper vaginal angle in the pelvic organ prolapse group were smaller than those in the non-prolapse group.The uterine body-PICSline angle and cervix-PICSline angle in the prolapse group were significantly smaller than those in the non-prolapse group,the middle-lower vaginal angle in the prolapse group was significantly larger than that in the non-prolapse group,the upper vaginal-PICSline angle and the middle vaginal-PICSline angle in the prolapse group were larger than those in the non-prolapse group,the lower vaginal-PICSIine angle in the prolapse group was smaller than that in the non-prolapse group,and the cervical length in the prolapse group was longer than that in the non-prolapse group.The uterine vaginal axis is shifted backward and downward as a whole in the standard coordinate system established in the sagittal position.2.Under the action of abdominal pressure load,the retroversion and flexion of the uterus occurred,the shape and position of the bottom of the uterus changed the most,the cervical orifice pointed to the coccyx region,and the cervical,middle and upper segment of vagina and levator anus muscle changed.The anterior and posterior wall of vagina,rectum and levator anus muscle all changed in different degrees.The shape and position deformation of levator anus muscle is larger than that of main ligament and uterine-sacral ligament,and the stress of levator anus muscle is the greatest.With the increase of abdominal pressure load,the maximum stress and maximum deformation of pelvic floor organs and tissues increase,and the stress injury of pelvic floor organs and tissues is more likely to occur.3.The abdominal pressure under different physiological conditions changed the morphological and positional characteristics of the main organs of the pelvis,especially the cervical region,the anterior and posterior vaginal fornix,the levator ani muscle and the bottom of the bladder.The maximum deformation of the intact pelvic floor support system was mainly distributed in the bottom of the uterus.The deformation of the bottom of the uterus gradually increased and shifted downward and posterior,while the moderate deformation was mainly distributed in the anterior and posterior wall of the vagina,the rectum and the middle and upper segment of the levator ani muscle.The stress distribution of the pelvic floor system is concentrated in the uterine floor,the cervical orifice,the bottom of the bladder,the anterior and posterior vaginal fornix and the middle and lower part of the vagina,and the levator anus muscle is close to the sacrococcyx region.With the increase of abdominal pressure load,the stress concentration area is transferred from the bottom of the bladder to the upper part of the vagina,the superior part of the rectum and the superior part of the levator anus muscle,and increases step by step.After the injury of the levator anus muscle,the stress that the levator anus muscle can bear is significantly reduced.After the injury of the levator ani muscle,part of the stress transferred to the perineal body,and the perineal body played an important supporting role after the injury of the levator anus muscle.with the increase of the degree of injury of the anterior vaginal wall,the deformation of the anterior vaginal wall increased.With the increase of abdominal pressure load,there is an important stress interaction between organs and inside organs,especially the sacrococcyx,Perineal body and levator anus muscle.4.A three-dimensional model of the pelvic floor of patients with pelvic organ prolapse and subjects without prolapse was constructed.compared with the healthy model,the bladder,uterus and vagina of the patients with prolapse dropped significantly,and the uterine body tilted backward and squeezed the bladder forward resulting in the forward movement of the bladder.the physiological curvature of uterus,vagina and rectum was lost,moved backward and downward,and the hiatus of levator anus was enlarged.On the basis of the three-dimensional model,an individual three-dimensional finite element model of the pelvic support system is further established,which confirms that there are differences in stress and deformation of different tissues and organs between healthy and prolapsed individuals under different stress conditions.the short-term stress of healthy pelvic tissue will not lead to obvious deformation under different abdominal pressure,and the curve of maximum deformation shows a non-linear trend with the increase of abdominal pressure.On the other hand,the short-term stress of pelvic floor tissues and organs of prolapse patients was obviously deformed,and the curve of maximum deformation showed a linear trend.The stress value of pelvic tissue of healthy subjects increased steadily with the increase of abdominal pressure under different abdominal pressure.The maximum stress of pelvic tissue in prolapse patients was significantly higher than that in non-prolapse patients under different abdominal pressure.It was confirmed that the morphological and stress characteristics of pelvic tissue in patients with prolapse under different abdominal pressure loads were significantly different from those in non-prolapsed subjects,especially in uterine floor,anterior vaginal wall,levator anus,bladder body and perineal body.it was preliminarily verified that the changes of tissue morphology of pelvic organ prolapse patients and non-prolapsed subjects under the same abdominal pressure had the mechanical supporting effect on pelvic floor organs.Conclusion(s):1.There are great differences in the axis,length and position of uterus and vagina between prolapse women and non-prolapse women.in prolapse women,the uterus is retroverted and flexion,the vagina shortens and turns to the ventral side and straightens,the uterus and vagina moves backward and downward and the mechanical axis deviates from the sacrum and coccyx.The change of mechanical axis and position of uterus and vagina is an important mechanism of pelvic organ prolapse.2.The two-dimensional equivalent mechanical finite element model can accurately reflect the biomechanical characteristics of female pelvic floor.The stress axial relationship of normal female pelvic floor is that the middle and upper segment of uterus and vagina mainly act on the sacrococcyx and levator anus,and the lower segment of vagina acts on the perineal body.The pelvic floor support system transfers the resultant force direction of abdominal pressure and organ weight to the direction pointing to the sacrococcyx.Sacrococcyx,levator ani muscle and perineal body play an important role in stress support in the pelvic floor system.3.The shape,position and stress characteristics of pelvic floor organs change obviously under different physiological conditions of abdominal pressure.when abdominal pressure increases,the stress and strain characteristics of pelvic floor tissues and organs are the comprehensive effect of the injury of levator anus,main ligament and uterine-sacral ligament.the formation of anterior vaginal wall prolapse is closely related to the injury of anterior vaginal wall.This study has important guiding significance for analyzing the mechanical principle of female pelvic floor support system and putting forward the corresponding solutions,and can help to improve the understanding of different forms of pelvic floor support structure damage.4.The three-dimensional anatomical model and three-dimensional finite element analysis can preliminarily reflect the three-dimensional anatomical and biomechanical characteristics of the pelvic floor supporting system of women with and without prolapse.The increase of abdominal pressure load changes the morphological and positional characteristics of the pelvic floor supporting structure,showing different stress and strain characteristics from the healthy pelvic floor.These anatomically accurate models can study the mechanism of pelvic organ prolapse under more real physiological conditions.The purpose of this study is to provide theoretical support for the clinical prevention and treatment of pelvic organ prolapse.The mechanical balance of pelvic floor support system in patients with prolapse is abnormal due to the change of tissue and organ morphology and structure position.in view of the mechanical imbalance of the pelvic floor,we put forward a new theory of stress injury of the pelvic floor and the finite element analysis model of the pelvic floor support system developed in this study.It can also be used to study the effects of different surgical methods of pelvic floor reconstruction involving changes in structural shape and mechanical properties,and may become a useful tool for improving pelvic floor reconstruction in the future.