Finite element model focused on stress distribution in the levator ani muscle during vaginal delivery

Ladislav Krofta,Linda Havelková,Jaroslav Feyereisl,Luděk Hynčík,Michal Krčmář,Iva Urbánková

doi:10.1007/s00192-016-3126-1

Ladislav Krofta, Linda Havelková + Show 4 more

Open Access

https://doi.org/10.1007/s00192-016-3126-1

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Abstract

Introduction and hypothesisDuring vaginal delivery, the levator ani muscle (LAM) undergoes severe deformation. This stress can lead to stretch-related LAM injuries. The objective of this study was to develop a sophisticated MRI-based model to simulate changes in the LAM during vaginal delivery.MethodsA 3D finite element model of the female pelvic floor and fetal head was developed. The model geometry was based on MRI data from a nulliparous woman and 1-day-old neonate. Material parameters were estimated using uniaxial test data from the literature and by least-square minimization method. The boundary conditions reflected all anatomical constraints and supports. A simulation of vaginal delivery with regard to the cardinal movements of labor was then performed.ResultsThe mean stress values in the iliococcygeus portion of the LAM during fetal head extension were 4.91–7.93 MPa. The highest stress values were induced in the pubovisceral and puborectal LAM portions (mean 27.46 MPa) at the outset of fetal head extension. The last LAM subdivision engaged in the changes in stress was the posteromedial section of the puborectal muscle. The mean stress values were 16.89 MPa at the end of fetal head extension. The LAM was elongated by nearly 2.5 times from its initial resting position.ConclusionsThe cardinal movements of labor significantly affect the subsequent heterogeneous stress distribution in the LAM. The absolute stress values were highest in portions of the muscle that arise from the pubic bone. These areas are at the highest risk for muscle injuries with long-term complications.

Highlights

Introduction and hypothesisDuring vaginal delivery, the levator ani muscle (LAM) undergoes severe deformation
The absolute stress values were highest in portions of the muscle that arise from the pubic bone
The descending fetal head initially distends the iliococcygeus muscle (ICm) portion of the LAM at station −3

Summary

Introduction

The levator ani muscle (LAM) undergoes severe deformation This stress can lead to stretch-related LAM injuries. This stress can lead to stretchrelated injuries, such as muscle tearing and striated muscle atrophy, owing to pudendal denervation [1], localized primarily to the region of the pubovisceral muscle (PVm) [2]. The PVm, known as the pubococcygeus muscle, needs to be stretched during vaginal birth to over three times its original length [3] This elongation is more than twice what the striated muscle can withstand without damage in a nonpregnant animal model [4]. On magnetic resonance imaging (MRI) the details of muscles are vivid, identifying the origin of this damage during vaginal birth [5]. Such muscle trauma, which is not visible after delivery by cesarean section, usually causes lifelong complications [6] and is associated with a significantly worse genital body image, poorer sexual health [7], and necessitates surgical treatment later in life [8]

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