Computational Modeling of Hard Tissue Response and Fracture in the Lower Cervical Spine under Compression Including Age Effects

computational modelling;cortical bone;trabecular bone;compression;age effect;constitutive model;fracture;anisotropy;asymmetry;element erosion;human body models

Khor, Fionaadvisor:Cronin, Duane ; affiliation1:Faculty of Engineering ; Cronin, Duane ;

University of Waterloo

关键词: human body models;    age effect;    Master Thesis;    element erosion;    anisotropy;    computational modelling;    asymmetry;    trabecular bone;    compression;    constitutive model;    cortical bone;    fracture;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/13432/4/Khor_Fiona.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Almost half of motor vehicle accident (MVAs) victims experience traumatic spinal cord injuries(SCI), which are often associated with rollover accidents. Specifically, rollovers have the highestincidence rate of AIS2+ cervical spine injuries and more than half of the patients with SCIsdemonstrated spine fractures with the majority being burst fractures. Detailed finite elementhuman body models (HBMs) have been utilized to assess the safety of occupants and pedestriansin crash scenarios, augmenting the results from crash test dummies in physical tests. HBMs canpredict the potential for injury and provide data such as fracture initiation and propagation that isnot possible to collect experimentally. Biofidelic HBMs capable of predicting tissue-level injuryrequire representative material properties and tissue level failure criteria. However, currentHBMs use simplified constitutive models and are not capable of predicting the fracture thresholdand fracture pattern for complex scenarios, such as the vertebrae in the neck. The objective ofthis study was to investigate constitutive models with age effect that are representative of corticaland trabecular hard tissues and assess the failure response of a C57 (C5-C6-C7) segment modelunder compression loading. Two sets of material properties were identified that corresponded to the lower age of theexperimental test samples (younger than 50 years old (YO)) and the higher age of the testsamples (older than 70 YO). The available constitutive models in a commercial finite elementcode (LS-DYNA) were reviewed and the constitutive models that best represent the cortical andtrabecular bone responses were analyzed. As there were no single constitutive model availablethat included all the key properties of hard tissues, asymmetric and anisotropic elastic-plastic(cortical) and crushable foam (trabecular) models were evaluated. Single element simulationswere performed to verify the constitutive models. A functional spinal unit (FSU) model wasextracted from a detailed 50th percentile HBM (Global Human Body Models Consortium(GHBMC) M50-O v4.3) and a centric compression simulation was performed to identify the bestperforming constitutive model compared to experimental data. Various eccentricity cases of thecompression experiments were simulated as well such as anterior, posterior and lateral. The anisotropic model predicted failure values and fracture patterns in better agreement with experimental data compared to an asymmetric or isotropic and symmetric model. This study showed the importance of including age effects that correspond to the age of experimental testsubjects. This study also showed that simulations could provide additional insight regardingfracture initiation and progression, which is challenging to measure in dynamic experiments.Gender, segment level, and strain rate effect were not included in this work, which arelimitations of the current study. In addition, the lack of human cervical spine experimental datafor improved model validation is another limitation of this study. In conclusion, this studysuccessfully utilized uncalibrated material properties of cortical and trabecular bone tissue fromliterature and accurately predicted failure outcomes of compression experiments with theimplemented constitutive models.