Biomechanical Model of the Levator Ani Muscle: Identifying the Greatest Strain Areas in Its Subdivisions

Purpose Childbirth subjects the levator ani muscle (LAM) to significant mechanical stress, potentially causing damage and complications like pelvic organ prolapse or incontinence. This study aims to investigate potential defects in the LAM due to mechanical loading during childbirth, using a computational biomechanical model to identify regions of high fibre deformation. Materials and Methods A finite element (FE) model of the pelvic floor was developed from a 3T MRI scan of a 23-year-old nulliparous woman. The pelvic structures were segmented and reconstructed, incorporating isotropic hyperelastic materials to simulate tissue. A 9.6 cm diameter sphere, simulating a foetal head, was passed along the pelvic axis to assess fibre deformation in the puborectalis muscle (PRM) and pubovisceralis muscle (PVM) during delivery. Results The model showed that the PVM experienced higher strain than the PRM, with peak elongation occurring at its pubic bone attachment. The PRM showed more even strain distribution along its length. The most loaded areas of the represented structures show large muscle deformations, which are observed at the muscle attachment site at both the PVM and the PRM, but also in the dorsolateral part of the PRM. Conclusions The computational model highlights high-strain regions in the LAM during childbirth, which may correlate with clinical observations of muscle injury. The pubovisceralis muscle appears to be more prone to damage due to greater localized strain, whereas the puborectalis muscle experiences more distributed strain. These findings increase our understanding of pelvic floor mechanics and may guide clinical assessment of pelvic floor dysfunction.