Neonatal brachial plexus palsy (NBPP) is an injury to newborn infants that occurs during the birthing process in 1.5/1,000 total births (1). About 2/10,000 total births result in an injury that persists past 12 months of age and leads to a permanent deficit in upper extremity function. When injuries to the brachial plexus occur, they may be classified based on reference to a historical definition: Erb’s palsy or Klumpke’s palsy. Erb’s palsy involves the C5/C6 nerve roots, while Klumpke’s palsy involves damage to the lower cervical and upper thoracic nerve roots (C8-T1). Based on previous research, it is known that both endogenous and exogenous forces can have a direct effect on the fetus during labor and delivery. Endogenous force refers to internal forces from the mother (uterine contractions and pushing), while exogenous force is an external force applied by the birthing attendant. This latter force may involve downward axial traction, aligned with the infant’s spine, or downward lateral traction on the neonatal head, which causes bending of the fetus’ neck away from the anterior shoulder. While the long term assumption that lateral, bending traction can cause enough stretch to result in a permanent injury has been confirmed through experimental and modeling studies, recent research also indicates that maternal forces – alone or in combination with axial traction – are also a likely cause of NBPP (1). However, the pattern of stretching within the complete neonatal brachial plexus has not been characterized. Further research is needed to understand how the various delivery forces stretch the five nerve roots of the brachial plexus to better understand the mechanisms of NBPP. Brachial plexus research on neonates is difficult to conduct, as these subjects are unavailable for research – especially research that may cause injury or requires the harvesting of tissues. Different ways to analyze the brachial plexus may include cadaveric, animal, and computational models. Computational models can give insight into brachial plexus injuries, as they can designate specific forces, dimensions, and material properties such that the specific effect of one parameter can be investigated. The objectives of this dissertation were to develop both a two-dimensional (2D) and a three-dimensional (3D) finite element model of the neonatal brachial plexus that can be validated based on previous in vitro experiments and clinical observations. Once validated, the model will be used to analyze which maternal, neonatal, and delivery factors may affect the stretch in the brachial plexus and therefore increase injury risk. Specifically, three objectives were established for this project: (1) Conduct statistical analysis of clinical NBPP data to better document the types of injuries that occur and their relationship to maternal and neonatal factors; (2) Develop and validate a 2D Model of the neonatal brachial plexus as an initial step in model development, which can then be used to investigate the effect of anatomical variations in a simplified structure; and (3) Develop and validate a 3D Model of the neonatal brachial plexus, which can then lead to an analysis of the effect that specific NBPP injuries have on the change of stress throughout the plexus. Altogether, these objectives offer advances in the world of computational modeling and biomechanical nerve injuries by providing useful insight for researchers, neurosurgeons, and other medical professionals to scientifically evaluate biomechanical aspects of neonatal brachial plexus injuries – in the hope to provide useful insight in ways to lessen the chances of these injuries occurring.
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