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

ObjectiveTo analyze the configuration of levator ani muscle in normal nulliparous women and women with pelvic organ prolapse(POP)using transperineal ultrasound,magnetic resonance imaging(Magnetic Resonance,Imaging,MRI)and the medical three-dimensional reconstruction technique.Then,with the application of the finite element simulation technology,to conduct preliminary study of the stress and strain characteristics of different configurations of levator ani muscle in normal nulliparous women,in order to provide imaging support in exploring the pathogenesis of POP.Methods120 normal nulliparous women and 80 POP women in our hospital were randomly selected as the research objects.The levator hiatus morphology was observed by transperineal ultrasonography and the function of puborectal muscle was further analyzed.At the same time,48 normal nulliparous women and 20 women with POP were randomly selected to perform MRI examination.Then,conduct the levator ani muscle reconstruction using Mimics software based on the levator ani muscle MRI images in order to observe the iliococcygeus morphology,measure iliococcygeus-related spatial configuration parameters and further analyze the configuration characteristics of the iliococcygeus.Furthermore,conduct preliminary study on the stress and strain characteristics of normal nulliparous women with different configuration iliococcygeus with the application of finite element simulation technology.ResultsThe morphology of puborectal muslce in normal nulliparous women was presented as a V on the pelvic cross-sectional images.The medial margin of pubic ramus and puborectal muscle constitute the levator hiatus,which was shown like a rhomboid in normal nulliparous women.The morphology of levator hiatus in nulliparous women can be divided into three types,including long type,intermediate type and flat type,according to the measurement results of puborectal muscle attachment angle.Each type accounted for 56%,31% and 12%.There were differences in the anteroposterior diameter,coronal diameter and area of the three type levator hiatus in normal nulliparous women.The contractility of the anteroposterior diameter of the levator hiatus was different in the three types.The morphology of puborectal muscle in women with POP was shown as a U on the pelvic cross-sectional images.The measurement results of levator hiatus morphological parameters was significantly different in normal nulliparous women and women with POP.The contractility of the anteroposterior diameter of the levator hiatus in women with POP was greater than normal nulliparous women.The distensibility of women with POP was significantly greater than normal nulliparous women.The general configuration of the iliococcygeus is like a butterfly wing and the levator plate is like a fornix based on the pelvic MRI image reconstruction.The iliococcygeus configuration of nulliparous women can be divided into three types according to the levator plate angle.The posterior angle of iliococcygeus and the levator plate curvature were both different among the three types.The configuration of the iliococcygeus in women with POP was like a loosely butterfly wing.The levator plate angle,the levator plate curvature,the length of iliococcygeus,the width of iliococcygeus and the posterior angle of iliococcygeus in women with POP was significantly larger than that of the nulliparous women.The finite element model of iliococcygeus established on different iliococcygeus configuration in nulliparous women presented different stress and strain characteristics under the same simulated abdominal pressure.ConclusionsPuborectal muslce is an important part of the levator ani muscle.The medial margin of pubic ramus and puborectal muscle constitute the levator hiatus,which was shown like a rhomboid in normal nulliparous women.It can be divided into three types in nulliparous women and the sizes of levator hiatus in different types were different.But the contractility and distensibility of levator hiatus in different types were of no significant difference.Compared with the nulliparous women,the morphology,size,contractility and distensibility of the levator hiatus in POP women were significantly different.Iliococcygeus is another important part of the levator ani muscle.The configuration of iliococcygeus in nulliparous women was like a butterfly wing and the levator plate was like a fornix.The configuration of iliococcygeus can be divided into three types.Different types of iliococcygeus configuration have different configuration and stress and strain characteristics.The configuration of iliococcygeus in women with POP loosely butterfly wing and was significantly changed compared with nulliparous women.