Development of Finite Element Models of Maternal Pelvis, Neonate and Brachial Plexus
Authors:   , Mounzer Marc Karam , Balasubramanian Sriram , Throckmorton Amy 
Published: November 2024

Shoulder dystocia (SD) is a serious obstetric emergency that occurs when the neonatal shoulders fail to deliver after the head has emerged during the second stage of labor. This condition can result in severe complications for both the neonate and the mother, including brachial plexus (BP) injuries, fractures, hypoxia, and postpartum hemorrhage. The most common injury associated with SD is BP injury, which results from overstretching of the nerves during shoulder impaction. BP injury can lead to neonatal brachial plexus palsy (NBPP), ranging from temporary palsy to loss of function of the upper limb. Due to ethical limitations, BP stretch cannot be studied in clinical deliveries, necessitating the use of three-dimensional computational models. Previous computational rigid-body models, which have been developed using MADYMO, have provided valuable insights into the mechanical effects of various forces and maneuvers encountered during complicated birthing scenarios. However, these models have significant limitations in their biofidelity due to the use of rigid body assumptions for soft tissues and the simplistic representation of the BP as a non-linear spring. To address these limitations, finite element (FE) models of the 50th percentile adult maternal pelvis, 90th percentile neonate and brachial plexus were developed with a goal to improve future computation simulation of SD. These FE models can accurately capture the deformation and distribution of forces in soft tissues during the birthing process by discretizing the maternal and neonatal structures into smaller elements. Furthermore, this approach allows for a detailed representation of the BP, considering its intricate structure and spatial relationships of its subsegments, which directly influence the stretch response of the nerves during a SD event. The incorporation of pelvic floor muscles in the FE model of the maternal pelvis also enables the quantification of resistance to neonatal descent, an essential factor in the biomechanics of delivery. To ensure both the accuracy and computational efficiency of these FE models, grid independence tests were conducted for all three FE models to determine the optimal element sizes for the FE meshes. The resulting high-quality hexahedral meshes consist of 3,308 elements for the maternal pelvis model, 61,577 elements for the neonatal model and 7,974 elements for the BP model. Through the development of these enhanced FE models, valuable insights can be gained into the forces and deformations experienced by the neonate and maternal tissues during SD and associated obstetric maneuvers. Such biofdeilic computational tools will lead to an improved understanding of injury mechanisms that will contribute to the development of more effective strategies for preventing and managing BP injuries associated with this obstetric emergency. Ultimately, this work seeks to advance the field of computational modeling in obstetrics and improve clinical outcomes for mothers and neonates affected by SD.