Content area
Full Text
ABSTRACT - Despite safety advances, thoracic injuries in motor vehicle crashes remain a significant source of morbidity and mortality, and rib fractures are the most prevalent of thoracic injuries. The objective of this study was to explore sources of variation in rib structural properties in order to identify sources of differential risk of rib fracture between vehicle occupants. A hierarchical model was employed to quantify the effects of demographic differences and rib geometry on structural properties including stiffness, force, displacement, and energy at failure and yield. Three-hundred forty-seven mid-level ribs from 182 individual anatomical donors were dynamically (~2 m/s) tested to failure in a simplified bending scenario mimicking a frontal thoracic impact. Individuals ranged in age from 4 - 108 years (mean 53 ± 23 years) and included 59 females and 123 males of diverse body sizes. Age, sex, body size, aBMD, whole rib geometry and cross-sectional geometry were explored as predictors of rib structural properties. Measures of cross-sectional rib size (Tt.Ar), bone quantity (Ct.Ar), and bone distribution (Z) generally explained more variation than any other predictors, and were further improved when normalized by rib length (e.g., robustness and WBSI). Cortical thickness (Ct.Th) was not found to be a useful predictor. Rib level predictors performed better than individual level predictors. These findings moderately explain differential risk for rib fracture and with additional exploration of the rib's role in thoracic response, may be able contribute to ATD and HBM development and alterations in addition to improvements to thoracic injury criteria and scaling methods.
KEYWORDS - thorax, fracture, force, energy, stiffness, strain, cross-section, geometry, cortical area, cortical thickness
INTRODUCTION
A tremendous effort has been put forth to reduce thoracic injuries sustained during motor vehicle crashes. Despite advances in vehicle safety measures, Brumbelow and Zuby (2009) still found that the thorax was the most injured body region in vehicles with "good" safety ratings for frontal crash scenarios (according to both NCAP and IIHS standards). This is due to the high-magnitude and rate of loads that can be placed on the thorax during such events (Kent et al. 2005; Lien et al. 2009; Pattimore et al. 1992) resulting in significant loss of structural integrity and associated soft tissue injury (e.g., lung contusion) particularly in children (Novakov et al....