正常女性盆底系统的二维等效力学建模方法与有限元分析

Two‑dimensional equivalent mechanical modeling and finite element analysis of normal female pelvic floor system

目的采用二维等效力学方法构建矢状面盆底的精细化几何模型,探讨不同腹压下盆底器官组织的形位改变对盆底生物力学特性的影响。方法纳入1名28岁身体健康、体形匀称的已婚未育女性志愿者,采用3.0 T磁共振扫描仪,仰卧位静息状态扫描盆底组织获得其盆腔核磁共振影像学数据。基于磁共振成像(MRI)二维参数测量和计算机辅助设计的方法,建立女性盆底的几何模型和有限元模型,分析不同腹压下盆底支持系统的生物力学变化特点。结果本研究在60、99、168、208 cmH_(2)O(1 cmH_(2)O=0.098 kPa)等4种腹压载荷作用下仿真模拟盆底受力的4种不同工况,分析得出的趋势为:在腹压载荷作用下子宫发生向下向后的后倾屈曲形位变化,宫颈、阴道中上段和肛提肌发生力学轴向指向骶尾骨的特征变化,肛提肌在水平方向上的变形比竖直方向上的更大。随腹压的增加健康受试者盆底整体系统在4种不同工况下的最大应力值分别为0.1943、0.3896、0.5571、0.6275 MPa,最大位移值分别为10、14、21、25 mm;宫颈和阴道中上段的最大应力值分别为0.1117、0.1618、0.2506、0.3041 MPa,最大位移值分别为3、6、9、11 mm;会阴体的最大应力值分别为0.0634、0.1196、0.2352、0.2880 MPa,最大位移值分别为1、2、4、5 mm;肛提肌最大应力值分别为0.1943、0.3896、0.5571、0.6275 MPa,最大位移值分别为2、4、7、8 mm;在不同工况下盆腔器官最大应力值及最大位移值均随腹压的增加而增加,正常女性盆底的应力轴向关系表现为子宫、阴道中上段主要作用于骶尾骨和肛提肌,阴道下段作用于会阴体。结论女性盆底系统二维等效力学建模和有限元分析方法可以较为准确地反映女性盆底的生物力学特征,盆腔器官应力的合力方向指向骶尾骨,骶尾骨、肛提肌和会阴体在盆底系统中具有重要的应力支持作用。

Objective To construct the geometric model of the pelvic floor by a two‑dimensional equivalent mechanics method,and to explore the effect of the shape and position of pelvic floor organs and tissues on the biomechanical properties of the pelvic floor under different abdominal pressure.Methods A 28‑year‑old healthy and symmetrical married infertile female volunteer was included.The pelvic floor tissue was scanned in the supine position using a 3.0T magnetic resonance scanner(Philips Company,Holland).Based on the method of magnetic resonance imaging(MRI)two‑dimensional parameter measurement and computer aided design,the geometric model and finite element model of the female pelvic floor were established,and the biomechanical characteristics of the pelvic floor support system under different abdominal pressure were analyzed.Results In this study,four different working conditions of the pelvic floor force were simulated under 60,99,168,and 208 cmH_(2)O(1 cmH_(2)O=0.098 kPa)abdominal pressure loads.The trend was as follows:under the abdominal pressure load,the retrograde flexion of the uterus occurred,the cervical,the middle and upper vaginal segment and the levator anus muscle had the characteristic change of mechanical axial direction pointing to the sacrum and coccyx,and the deformation of the levator anus muscle in the horizontal direction was greater than that in the vertical direction.With the increase of the abdominal pressure,the maximum stress values of the pelvic floor whole system of healthy subjects under four different working conditions were 0.1943,0.3896,0.5571,and 0.6275 MPa,respectively,and the maximum displacement values were 10,14,21 and 25 mm,respectively.The maximum stress values of the cervical and vaginal middle and upper segment were 0.1117,0.1618,0.2506,and 0.3041 MPa,respectively,and the maximum displacement values were 3,6,9,and 11 mm,respectively.The maximum stress of the perineal body was 0.0634,0.1196,0.2352,and 0.2880 MPa,and the maximum displacement was 1,2,4,and 5 mm.The maximum stress values of the levator anus muscle were 0.1943,0.3896,0.5571,and 0.6275 MPa,and the maximum displacement values were 2,4,7,and 8 mm,respectively.The maximum stress and maximum displacement of pelvic organs increased with the increase of the abdominal pressure under different working conditions.The stress axial relationship of normal female pelvic floor was that the middle and upper segment of uterus and vagina mainly acted on the sacrococcyx and the levator anus muscle,and the lower vaginal segment acts on the perineal body.Conclusions The two‑dimensional equivalent mechanical modeling and finite element analysis of the female pelvic floor system can accurately reflect the biomechanical characteristics of the female pelvic floor,and the resultant stress direction of the pelvic organs points to the sacrum and coccyx.The sacrum and coccyx,levator anus and perineal body play important stress supporting roles in the pelvic floor system.