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Development of an Age-Dependent Thoracic Injury Criterion for Frontal Impact Restraint Loading
Published May 19, 2003 by National Highway Traffic Safety Administration in United States
Data from 93 human cadaver tests (age range 17-86 years, mean 60.2, S.D. 13.3) were used to develop thoracic injury risk functions for frontal loading. The set of potential predictors included the maximum chest deflection, the age of the cadaver at death, the cadaver's gender, and the loading condition on the anterior thorax: blunt hub (41 tests), seat belt (26 tests), air bag (12 tests), and combined belt-and-bag (14 tests). Predicted outcomes were the probability of any rib fractures (onset of injury) and the probability of greater than six rib fractures (severe injury). Linear logistic regression models were used with the outcome modeled as a binary response (injury, no injury). It is shown that the injury risk function is not dependent on the loading condition (e.g., the 50% risk of injury does not change when the loading condition changes), but that the injury risk function is strongly dependent on the age of the cadaver at death. A significant injury risk model with good ability to discriminate injury from noninjury tests (p < 0.0001, Chi-square = 21.49, area under ROC = 0.867, Kruskal's Gamma \ma 0.732) is presented using only maximum chest deflection and cadaver age as predictors of injury risk. The 50% risk of any rib fractures is found to occur at 35% chest deflection for a 30-year-old, but at 13% deflection for a 70-year-old. The 50% risk of severe injury is shown to occur at 33% chest deflection for a 70-year-old, but at 43% for a 30-year-old.