Sex-Specific Differences in Thoracic Injury Prevalence and Causation in Frontal Motor Vehicle Crashes

Introduction:: Thoracic injuries are one of the most common and severe outcomes of motor vehicle crashes for front seat occupants. These injuries can affect various structures and organs in the chest cavity, such as the ribs, lungs, heart, and aorta, and can compromise the function of the respiratory and circulatory systems. Thoracic injuries can also lead to significant morbidity and mortality, especially in cases of multiple rib fractures, hemothorax, pneumothorax, pulmonary contusion, cardiac tamponade, and aortic rupture [1]. Previous research has suggested that sex may play a role in the risk and severity of thoracic trauma, as females have been shown to have a greater risk of Abbreviated Injury Scale (AIS) 2+ and AIS 3+ severity injuries compared to males across most injury types [2], including thoracic fractures. However, the mechanisms and sources of injury that account for these sex-specific differences are not well understood. The objective of this study was to investigate the sex-specific differences in thoracic injury prevalence and causation among occupants involved in frontal motor vehicle crashes using the Crash Injury Research and Engineering Network (CIREN) database. The CIREN database provides detailed information on motor vehicle crashes with recorded thoracic injuries, including injury type, location, severity, and causation. This study aimed to identify and quantify the sex-specific disparities in thoracic injury patterns and causation among seriously injured first row motor vehicle crash occupants.


Materials and Methods:: This study used motor vehicle crashes from the CIREN database years 2005 to 2015. The study sample consisted of 460 front seat CIREN occupants (n=204 males; n=256 females) who sustained thoracic injuries with an AIS severity of two or higher. Of the occupants analyzed, 371 (81%) were drivers (52% female) and 89 (19%) were right front passengers (72% female). The following variables were extracted for each occupant: age, sex, weight, height, change in vehicle velocity (delta-v), seatbelt status, occupant position, frontal airbag deployment, injury presence, primary involved physical component (IPC), and alternate IPCs, with IPC referring to the physical component within the vehicle that was determined as the source of the thoracic injury.

Injuries were categorized into seven groups: rib fracture, sternum fracture, hemo/pneumothorax, lung injury, heart injury, diaphragm injury, and vessel injury. Chi-squared tests were performed to examine associations between injury types and sex. Additionally, rib fracture localizers were used to identify which specific ribs were fractured. Fracture frequency by rib level was plotted for male and female: belted drivers, belted passengers, and unbelted occupants.

For injury causation analysis, IPCs were categorized into seven separate groups: Steering Wheel, Instrument Panel, Door, Seatbelt, Airbag, Interior, and Other Causes. Chi-squared tests were performed to examine the associations between each IPC group and sex. P-values were reported and interpreted for all statistical analyses.


Results, Conclusions, and Discussions:: Results: Females were belted more often than males (p=0.0061) and were less likely to be a driver (p< 0.001; Table 1). Average delta-v was 5 km/hr higher for males compared to females (p=0.001). Male height and weight were higher (p< 0.0001), but there were no sex differences for body mass index (BMI), age and airbag deployment. There were 860 AIS 2+ thoracic injuries sustained by the 460 occupants (Table 2). Lung injuries were more prevalent among males (p=0.01). Incidence of rib/sternum fractures, and injuries to the heart, diaphragm, and vessels did not differ by sex.

In belted drivers (Figure 1), more right-sided rib fractures were sustained by females (79.4%) vs. males (71.0%). In belted passengers, more left-sided rib fractures were sustained by males (68.0%) vs. females (48.3%). Unbelted males and females had similar and relatively symmetric rib fracture patterns (left-sided fractures: 60.2% males; 54.9% females). The steering wheel was more commonly the source of injury in males (37.5%) vs. females (22.7%; Table 3). However, females were more likely to have injuries attributed to the seat belt (p=0.0001).



Discussion/Conclusions: This study investigated sex-specific differences in thoracic injury prevalence and causation in frontal crashes. Males had a higher prevalence of thoracic injury, possibly due to anatomical, physiological, and biomechanical factors that may influence the susceptibility and response to thoracic injury. Sex-differences in rib fracture patterns and the injury source (e.g., steering wheel, seatbelt) align with prior research [3], and may reflect sex-differences in body size, posture, seat position, and belt fit that influence chest contact and loading patterns in motor vehicle crashes.

These results have implications for the prevention and management of thoracic trauma between sexes and highlight the need for detailed data collection on injury causation and mechanisms in motor vehicle crashes. Such data could identify factors that influence thoracic injury occurrence and outcomes, leading to more effective prevention and treatment strategies. These findings indicate that sex-specificity should be considered in the development and assessment of vehicle safety systems and occupant protection.


Acknowledgements (Optional): : Funded by National Highway Traffic Safety Administration (NHTSA).

References (Optional): : [1] Fadl SA, Sandstrom CK. Pattern Recognition: A Mechanism-based Approach to Injury Detection after Motor Vehicle Collisions. Radiographics. 2019 May-Jun;39(3):857-876.

[2] Evans, J., McGwin, G., & Metzger, J. (2004). Sex differences in injury severity and outcome measures after motor vehicle collisions. Journal of Trauma and Acute Care Surgery, 56(4), 880-884.

[3] Forman, J., Poplin, G. S., Shaw, C. G., McMurry, T. L., Schmidt, K., Ash, J., & Sunnevang, C. (2019). Automobile injury trends in the contemporary fleet: Belted occupants in frontal collisions. Traffic injury prevention, 20(6), 607-612.