The stress and strain of the second stage vaginal delivery: an analysis based on three-dimensional model of pelvic floor muscle
XUAN Rongrong1, ZHANG Yongyan1, GAO Yajie2, REN Shuaijun2, LI Jialin2, YANG Zhenglun2, ZHU Jue3, OUYANG Menglin4
1.Department of Obstetrics and Gynecology, the Affiliated Hospital of Medical School, Ningbo University, Ningbo 315020, China; 2.School of Medicine, Ningbo University, Ningbo 315211, China; 3.Key Laboratory of Impact and Safety Engineering, Ningbo University, Ningbo 315211, China;4.Department of Anesthesiology, the Affiliated Hospital of Medical School, Ningbo University, Ningbo 315020,China
XUAN Rongrong,ZHANG Yongyan,GAO Yajie, et al. The stress and strain of the second stage vaginal delivery: an analysis based on three-dimensional model of pelvic floor muscle[J]. JOURNAL OF WEZHOU MEDICAL UNIVERSITY, 2021, 51(8): 623-631.
Abstract：Objective: To explore the possible degree and location of pelvic floor muscle injury caused by different fetal biparietal diameter during the second stage of vaginal delivery. Methods: Data of female pelvic floor magnetic resonance imaging (MRI) were collected and the pelvic floor muscle model was re-established by 3D modeling. Then the responding mechanism of pelvic floor muscle in the second labor process was investigated by finite element method. Stress analysis, strain analysis and maximum displacement analysis were made based on the simulation of three different fetal head models. Results: Three kinds of fetal biparietal diameter models were successfully established through the three-dimensional model of pelvic floor muscle, which was respectively 80 mm (D80), 90 mm (D90) and 100 mm (D100). The stress analysis showed that the maximum equivalent stress of the D80, D90 and D100 were 0.0782, 0.0804 and 0.2509 MPa respectively at 0.15 s. The larger the biparietal diameter of fetus, the greater the maximum equivalent stress, with the maximum principal stress of pelvic floor muscle and the peak value at the attachment of the pubococcygeus to the skeleton. The strain analysis showed that the principal strain value of D80, D90 and D100 was 0.3215, 0.3336 and 0.2710 MPa at 0.15 s, respectively.The larger the biparietal diameter of the fetus, the greater the maximum principal strain of the pelvic floor muscle,with the peak value in the pubic coccygeus muscles, or at the place where the pelvic floor muscle attached to the skeleton. The maximum displacement analysis showed that the maximum displacement difference in Z direction of D80, D90 and D100 models was 50.36, 50.68 and 52.51 mm respectively, and the maximum displacement in X direction was 127.11, 140.21 and 129.38 mm respectively. The displacement nephogram showed that the whole pelvic floor muscle had a huge deformation in the second stage of labor, in which levator ani muscle was stretched obviously, which was 128.90%-131.27% in the vertical direction (mainly the pubococcygeal muscle) and 181.59%-200.30% in the horizontal direction. Conclusion: In the second stage of vaginal delivery, the larger the biparietal diameter of the fetus, the greater the maximum equivalent stress and the maximum principal stress of the pelvic floor muscle, the greater the maximum principal strain, with the peak value all appearing at the attachment ofthe pubococcygeus to the skeleton. In the second stage of labor, the whole pelvic floor muscle had a huge deformation, and the levator ani muscle, especially the pubococcygeus part, was the most stretched muscle.
