Preliminary Study On The Configuration And Mechanical Properties Of Levator Ani Muscle In Nulliparous Women And Postpartum Women

ObjectivesTo analyze the configuration of levator ani muscle(LAM)in nulliparous women and postpartum women using transperineal ultrasonography,magnetic resonance imaging(MRI)and three-dimensional reconstraction technique.With the application of the finite element method,to conduct the preliminary analysis of the stress and stretch distributions of different configurations of LAM in nulliparous and postpartum women,in order to investigate the mechanical mechanism of the pelvic organ dysfunction.Methods50 cases of nulliparous women and 150 postpartum women who were treated in our hospital from September 2016 to December 2018 were randomly selected as subjects.The transperineal ultrasounography was used to observe the morphology and function of the levator hiatus.The pelvic floor MRI was performed one week followed by ultrasound examinations.Compare and judge the classification of LAM defects by two imaging methods.The Mimics software was used to reconstruct the pelvic floor structure from magnetic resonance images.Furthermore,the finite element method was applied to the three-dimensional model of various types of LAM,and the load was simulated to study the mechanical properties.ResultsWith the diagnosis of the transperineal ultrasonography and MRI,the LAMs of 50 nulliparous women were intact and structurally symmetrical.Meanwhile,30(20%)of 150 postpartum women found LAM defects.The kappa value of the transperineal ultrasonography and MRI to determine whether the LAM is damaged is 0.916,and the diagnostic kappa value of the LAM injury content is 0.764.Compared with the intact LAM group,in the Valsalva period,the parameters of levator hiatus in injury group was significantly larger than the LAM intact group.The parameters of contractile and diastolic performance in the LAM injury group were significantly different with those in the LAM group(P<0.05).In the LAM injury group,there were statistical differences in the parameters related to contraction and diastolic performance between injury types.According to the levator plate angle,the intact LAM configuration can be divided into type ?,type ?,type ? and type ?.The vertical height of the levator plate,the anteroposterior diameter of the LAM and the anteroposterior diameter of the pelvic outlet were statistically different.The injured LAM can be divided into partial or complete injury,unilateral injury or bilateral injury.The maximum stress values of intact LAM models are located in the LAM-pubic symphysis,and the distribution of stress and stretch of each type of intact LAM is different.The maximum stress value of each type of injured LAM model is positioned in the joint of LAM-pubis or the tendinous arch of LAM.There are differences in the stress-strain distribution of various LAM defect models.ConclusionsThe LAM injury often occurs in the joint of LAM-pubis,followed by the tendinous arch of LAM.MRI and transperineal ultrasonography have a very high consistency in the judgement of LAM injury,but there is a difference in the diagnosis of LAM injury.Iliococcygeus injury can only be obtained by MRI,and the transperineal ultrasonography is limited in observing iliococcygeus injury.The LAM injury affects the systolic and diastolic functions.The effects of various types of LAM injury on contraction and diastolic functions are different.Combination of the three-dimensional reconstruction and the finite element method can effectively analyze the configuration and biomechanical properties of LAMs.The distributions of stress and strain have implications for the location and the risk of damage.There are differences in the configuration parameters and stress-stretch distributions of various types of intact LAMs.There are also differences in different types of injuries.From the perspective of mechanics,the destruction of the LAM integrity causes uneven force on both sides of the LAM under abdominal pressure,resulting in a decrease in the ability to carry abdominal pressure.The instability of pelvic supportive system is one of the causes of pelvic organ prolapse.