Quantification of Skeletal and Soft Tissue Contributions to Thoracic Response in a Dynamic Frontal Loading Scenario

The I-PREDICT 50th Percentile Male Finite Element Model: Development and Validation of the Torso

Behind Armor Blunt Trauma (BABT) is a phenomenon that occurs when energy is transferred from Personal Protective Equipment (PPE) to the human body and can range from minor to fatal injuries. The current standard to evaluate PPE uses Roma Plastilina No. 1 clay and has a poor correlation to human injuries. To provide a more suitable human surrogate for evaluating risk of injury and functional incapacitation due to BABT, the Incapacitation Prediction for Readiness in Expeditionary Domains: an Integrated Computational Tool (I-PREDICT) has developed a 50th percentile male human body model (HBM) to better understand injury mechanisms in the BABT environment. The model was developed using a hierarchical validation approach including component, regional, and whole torso level tests. Material properties were sourced from literature and I-PREDICT experimental test data, and the model was simulated in 25 different validation cases ranging from component level quasi-static tests to high-rate BABT impacts. The model was stable in all 25 simulations. CORrelation and Analysis (CORA) and BioRank were used to objectively quantify the model response. The average CORA and BioRank across all validation cases were 0.78 ± 0.18 and 0.68 ± 0.27, respectively, indicating 'good' agreement by CORA standards and 'excellent' by BioRank standards. When compared to high-rate BABT experimental impacts on post-mortem human subjects, the I-PREDICT HBM accurately predicted rib fracture probability. The ultimate goal of the I-PREDICT model is to predict injury and functional incapacitation for various in theater military applications. This study highlights the development and validation of the I-PREDICT torso and highlights initial BABT use cases.

Comparison of Bending Properties in Paired Human Ribs with and without Costal Cartilage

Thoracic injuries, most frequently rib fractures, commonly occur in motor vehicle crashes. With an increased reliance on human body models (HBMs) for injury prediction in various crash scenarios, all thoracic tissues and structures require more comprehensive evaluation for improvement of HBMs. The objective of this study was to quantify the contribution of costal cartilage to whole rib bending properties in physical experiments. Fifteen bilateral pairs of 5th human ribs were included in this study. One rib within each pair was tested without costal cartilage while the other rib was tested with costal cartilage. All ribs were subjected to simplified A-P loading at 2 m/s until failure to simulate a frontal thoracic impact. Results indicated a statistically significant difference in force, structural stiffness, and yield strain between ribs with and without costal cartilage. On average, ribs with costal cartilage experienced a lower force but greater displacement with a longer time to fracture compared to isolated ribs. Comparisons were complicated by varying levels of calcification between costal cartilages and varying geometry with the inclusion of the costal cartilage. This study highlights the important effects of costal cartilage on rib properties and suggests an increased focus on costal cartilage in HBMs in future work.

Influences of human thorax variability on population rib fracture risk prediction using human body models

Rib fractures remain a common injury for vehicle occupants in crashes. The risk of a human sustaining rib fractures from thorax loading is highly variable, potentially due to a variability in individual factors such as material properties and geometry of the ribs and ribcage. Human body models (HBMs) with a detailed ribcage can be used as occupant substitutes to aid in the prediction of rib injury risk at the tissue level in crash analysis. To improve this capability, model parametrization can be used to represent human variability in simulation studies. The aim of this study was to identify the variations in the physical properties of the human thorax that have the most influence on rib fracture risk for the population of vehicle occupants. A total of 15 different geometrical and material factors, sourced from published literature, were varied in a parametrized SAFER HBM. Parametric sensitivity analyses were conducted for two crash configurations, frontal and near-side impacts. The results show that variability in rib cortical bone thickness, rib cortical bone material properties, and rib cross-sectional width had the greatest influence on the risk for an occupant to sustain two or more fractured ribs in both impacts. Therefore, it is recommended that these three parameters be included in rib fracture risk analysis with HBMs for the population of vehicle occupants.

A Novel Approach to Scaling Age-, Sex-, and Body Size-Dependent Thoracic Responses using Structural Properties of Human Ribs

Thoracic injuries are frequently observed in motor vehicle crashes, and rib fractures are the most common of those injuries. Thoracic response targets have previously been developed from data obtained from post-mortem human subject (PMHS) tests in frontal loading conditions, most commonly of mid-size males. Traditional scaling methods are employed to identify differences in thoracic response for various demographic groups, but it is often unknown if these applications are appropriate, especially considering the limited number of tested PMHS from which those scaling factors originate. Therefore, the objective of this study was to establish a new scaling approach for generating age-, sex-, and body size- dependent thoracic responses utilizing structural properties of human ribs from direct testing of various demographics. One-hundred forty-seven human ribs (140 adult; 7 pediatric) from 132 individuals (76 male; 52 female; 4 pediatric) ranging in age from 6 to 99 years were included in this study. Ribs were tested at 2 m/s to failure in a frontal impact scenario. Force and displacement for individual ribs were used to develop new scaling factors, with a traditional mid-size biomechanical target as a baseline response. This novel use of a large, varied dataset of dynamic whole rib responses offers vast possibilities to utilize existing biomechanical data in creative ways to reduce thoracic injuries in diverse vehicle occupants.