When involved in vehicle accidents, the fatality rate of thoracic injury is high, following head injury, and the major causality is a rise of organ injury rates due to an increase in the Number of Fractured Ribs (NFR). Previous studies suggested a high correlation between thoracic deflection and NFR. However, the correlation was evaluated primarily using test data in frontal collisions with restraint systems such as seatbelts or airbags. Thus, it was not evaluated by local loading. The objective of this paper is to evaluate the correlation between the thoracic deflection criteria and NFR under local loading conditions by thoracic impactor loading.
In order to evaluate the relationship between thoracic deflection criteria and NFR by localized loading, thoracic impact is more proper than sled impact, in which loading location and direction depend on restraint systems. Impact simulations were conducted on 19 points to cover the whole right side of the thorax. The simulations were conducted with the Global Human Body Model Consortium (GHBMC) 50th percentile male model for LS-DYNA. Deflection of each rib was measured at its anterior tip and Rmax was calculated using the deflections on the 4th rib and the 7th rib to represent Anthropometric Test Dummy (ATD) measurement points. In addition, Average Deflection of All Ribs (ADAR) and Weighted Average Deflection of All Ribs (WADAR) were calculated as proposed criteria. Then the correlation between NFR and each of those criteria was evaluated using the correlation coefficient.
The results showed that some specific impact points lower the correlation between NFR and Rmax. Impacts around 1st through 3rd ribs incur rib fractures without deflection on the representative points because the sternum and costal cartilage do not transmit the force and deflection to other ribs. On the other hand, ADAR showed a higher correlation with NFR than Rmax, and WADAR further improved correlation with NFR.
The results showed that WADAR needs to be taken into account to improve correlation between NFR and thoracic deflection. It suggests that deflection of all ribs modified by homogeneity of each rib deflection need to be considered in order to properly evaluate rib fractures caused by localized loadings.
The thoracic deflection criterion using weighted average deflection of all ribs showed the highest correlation with NFR and it allows evaluating rib fractures even under localized loading conditions.