Reducing chest injuries in automobile collisions: rib fracture timing and implications for thoracic injury criteria.

The purpose of this study was to quantify the biomechanical response of the human thorax during dynamic shoulder belt loading representative of that seen in a severe automotive collision. Two post-mortem human surrogates (PMHSs) (one male and one female) were instrumented with 26 single-axis strain gages on the ribs, sternum, and clavicle. The thorax of each PMHS was placed on a custom spine support bracket designed to support the thorax on either side of the spinous process, thereby allowing free motion at the costovertebral joints. In addition, the support bracket raised the thorax above the flat base plate, which could otherwise constrain the deformation and motion of the posterior region of the rib cage. The thorax of each PMHS was then loaded using a custom table-top belt loading system that generated thoracic displacement rates representative of a severe automotive collision, 1.3 m/s for the male PMHS and 1.0 m/s for the female PMHS. The rib fracture timing data, determined by analyzing the strain gage time histories, showed that severe thoracic injury (AIS = 3) occurred at 16% chest compression for the male and 12% chest compression for the female. However, these values are well below the current thoracic injury criteria of 29% chest compression for the male and 23% chest compression for the female. This data illustrates that serious thoracic injury (AIS = 3) occurs at lower chest compressions than the current ATD thoracic injury criteria. Overall, this study provides critical data that can be used in the design and validation of advanced ATDs and finite element models, as well as the establishment of improved, more stringent thoracic injury criteria.

Rib fracture timing in dynamic belt tests with human cadavers.

The purpose of this article is to present data from dynamic belt loading tests on the thorax of human cadavers where the exact timing of all rib fractures is known. To quantify rib fracture timing, a total of 47 strain gages were placed throughout the thorax of two human cadavers (one male, one female). To simulate thoracic loading observed in a severe car crash, a custom table-top belt loading device was developed. The belt loading pulse was configured to result in approximately 40% chest compression during a 150 ms load and unload cycle. The time histories of each strain gage were analyzed to determine the time of each rib fracture which was then directly compared with the reaction loads and chest displacements at that exact time, thereby creating a noncensored data set. In both cadavers, all rib fractures occurred within the first 35% compression of the thorax. As a general trend, fractures on the left side of the thorax, where the passenger belt passed over the abdomen, occurred first followed by fractures to the upper ribs on the right side of the thorax. By utilizing this technique, the exact timing of each injury level can be characterized relative to the mechanical parameters. For example, using rib fractures as the parameter for Abbreviated Injury Scale (AIS) scores in the female test, it was shown that AIS 1 injury occurred at a chest compression of 21.1%, AIS 2 at 21.6%, AIS 3 at 22.0%, and AIS 4 at 33.3%.