The objective of the study was to determine the biomechanics of the human thorax in a simulated frontal collision. Sled tests were conducted using unembalmed human cadavers at velocities of 32 or 48 kph. Specimens were restrained using air bag - knee bolster, air bag - lap belt, or air bag - three-point belt combinations. Two chest bands were placed at the upper and lower levels of the thorax to derive the deformation contours during impact. Radiography and detailed pathological evaluations were conducted. Differences in thoracic deformation contours between the upper and lower levels of the chest as well as among the various restraint system combinations were analyzed. High-speed photographs from the onboard and offboard cameras were analyzed for the quantification of specimen kinematics during impact. Thoracic trauma was assessed based on the abbreviated injury scale using autopsy findings;​ the trauma using clinical radiographs were compared with the injuries identified at autopsy. Three-point bending experiments were conducted on isolated rib specimens from each test according to accepted procedures.

Deformation contours derived from the chest bands indicated regional differences in the biodynamic response. Nondisplaced rib fractures occurred Without internal injuries or without the laceration of the costal pleura through the fractured rib. Furthermore, the number of rib fractures identified on routine clinical radiographs were consistently smaller than the number found at autopsy. These results indicate that there may be an overrating of thoracic trauma based on the abbreviated injury scale using rib fractures identified at autopsy in contrast to clinical radiography. Further studies are however, required to develop a scaling factor for the thoracic trauma based on autopsy findings. The mechanism of rib trauma Was determined to be compression and/or bending-related for the air bag - three-point belt restraint system wherein fractures were concentrated around the shoulder harness region and the lateral-most area of the rib cage 0n the right side. The mechanism of skeletal injury for the air bag - knee bolster system was secondary to a compressive force directed along the anteroposterior axis and applied bilaterally over the lower regions of the torso. Based on analysis of the contours, kinematics and injury mechanisms, the biomechanical response of the thorax is different between air bag - three-point belt loading, compared to the air bag - knee bolster restraint combinations.