A subject-specific anisotropic visco-hyperelastic finite element model of female pelvic floor stress and strain during the second stage of labor

• Published in: Journal of biomechanics Vol. 45; no. 3; pp. 455 - 460
• Main Authors: Jing, Dejun, Ashton-Miller, James A, DeLancey, John O.L
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 02.02.2012; Elsevier; Elsevier Limited
• Subjects: Adult; Anisotropy; Biological and medical sciences; Biomechanical Phenomena; Birth; Birth defects; Cesarean section; Childbirth & labor; Computer Simulation; Computerized, statistical medical data processing and models in biomedicine; Conflicts of interest; Delivery. Postpartum. Lactation; Elasticity; Female; Finite Element Analysis; Gynecology. Andrology. Obstetrics; Humans; Imaging, Three-Dimensional - methods; Injuries; Injury; Labor; Levator ani muscle; Mathematical models; Medical sciences; Models and simulation; Muscle Contraction; Muscles; Pelvic Floor - anatomy & histology; Pelvic Floor - physiology; Physical Medicine and Rehabilitation; Pregnancy; Risk; Sprains and Strains - physiopathology; Strain; Stresses; Stretch; Visco-hyperelastic; Stretch; Visco-hyperelastic; Levator ani muscle; Birth; Labor; Injury; Human; Perineum; Stress strain; Nuclear magnetic resonance imaging; Modeling; Hyperelasticity; Biomechanics; Finite element method; Pelvic floor; Anisotropy; Medical imagery; Female; Delivery; Woman; Biomedical engineering
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2011.12.002

Abstract Objectives To develop an improved model representation of the biomechanics of the levator muscles during the second stage of labor and to use a sensitivity analysis to explore the pathomechanics of levator muscle injury. Methods A subject-specific finite element model of human pelvic floor and fetal head was developed based on in vivo MRI data of a fetal head and maternal pelvis. An anisotropic visco-hyperelastic constitutive model employed material parameters estimated from biaxial tests on pelvic floor tissues. Boundary conditions reflected both anatomic constraints and the curve of Carus. A short second stage of labor, scaled to 10 min, was then simulated using a single expulsive push made in the absence of levator co-contraction. Results Large levator stresses occurred near the levator hiatus reaching 9 MPa at the pubovisceral muscle enthesis. The dominant principal stresses were located at, and aligned with, the edge of the hiatus. Muscle stretch bordering the levator hiatus was inhomogeneous: the average levator stretch was 3.55 with a high of 4.64 at the pubovisceral muscle enthesis. Decreasing perineal body stiffness by 40%, 50%, and 60% led to reductions in the maximum principal stretch ratio at the pubovisceral muscle enthesis of 8%, 13%, and 18%, respectively. Conclusions The pubovisceral muscle enthesis and the muscle near the perineal body are the regions of greatest strain thereby placing them at highest risk for stretch-related injury. Decreasing perineal body tissue stiffness significantly reduced tissue stress and strain, and therefore injury risk, in those regions.