Li Xinshan, Kruger Jennifer A, Nash Martyn P, Nielsen Poul M F
Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
J Biomech Eng. 2010 Nov;132(11):111010. doi: 10.1115/1.4002558.
The role of the pelvic floor soft tissues during the second stage of labor, particularly the levator ani muscle, has attracted much interest recently. It has been postulated that the passage of the fetal head through the pelvis may cause excessive stretching of the levator ani muscle, which may lead to pelvic floor dysfunction and pelvic organ prolapse later in life. In order to study the complex biomechanical interactions between the levator ani muscle and the fetal head during the second stage of labor, finite element models have been developed for quantitative analysis of this process. In this study we have simulated vaginal delivery using individual-specific anatomical computer models of the pelvic floor interacting with a fetal head model with minimal restrictions placed upon its motion. Two constitutive relations were considered for the levator ani muscle (of exponential and neo-Hookean forms). For comparison purposes, the exponential relation was chosen to exhibit much greater stiffening at higher strains beyond the range of the experimental data. We demonstrated that increased nonlinearity in the elastic response of the tissues leads to considerably higher (56%) estimated force required for delivery, accompanied by a more homogeneous spatial distribution of maximum principal stretch ratio across the muscle. These results indicate that the form of constitutive relation beyond the presently available experimental data markedly affects the estimated function of the levator ani muscle during vaginal delivery, due to the large strains that occur. Further experimental data at higher strains are necessary in order to more reliably characterize the constitutive behavior required for modeling vaginal childbirth.
在分娩第二阶段盆底软组织的作用，尤其是肛提肌，最近引起了人们的极大兴趣。据推测，胎儿头部通过骨盆可能会导致肛提肌过度拉伸，这可能会在日后导致盆底功能障碍和盆腔器官脱垂。为了研究分娩第二阶段肛提肌与胎儿头部之间复杂的生物力学相互作用，已经开发了有限元模型来对这一过程进行定量分析。在本研究中，我们使用盆底的个体特异性解剖计算机模型与运动限制最小的胎儿头部模型相互作用来模拟阴道分娩。考虑了肛提肌的两种本构关系（指数形式和新胡克形式）。为了进行比较，选择指数关系以在超出实验数据范围的更高应变下表现出更大的硬化。我们证明，组织弹性响应中增加的非线性会导致分娩所需的估计力显著更高（56%），同时最大主拉伸比在肌肉上的空间分布更加均匀。这些结果表明，由于会出现大应变，超出目前可用实验数据的本构关系形式会显著影响阴道分娩期间肛提肌的估计功能。为了更可靠地表征模拟阴道分娩所需的本构行为，需要更高应变下的进一步实验数据。
