Lower-Back Loads In Rear-End Collisions
Lower-back injuries are commonly reported after rear-end collisions. In fact, only neck injuries are reported more often. Numerous studies have analyzed cervical spine motion and loads in low-speed rear-end collisions, but few have addressed the lumbar spine. In this study, we analyzed lumbar compression in low-speed rear-end collisions to determine lower-back loads, how and when peak loading occurs, and the associated body motions.
In a rear-end collision, occupants move backward relative to the vehicle interior: the torso is supported by the padded seat back, and the head often contacts the padded head restraint. Exponent’s analysis of low-speed rear-end crash data from instrumented vehicles and crash-test dummies found that peak lumbar compression usually occurs not during the impact phase—when stretching of the torso along the seat back actually reduces lumbar compression—but after the impact as the occupant moves forward and settles back into the seat in an upright position. In the low-speed collisions reviewed, peak lumbar compression was much less than the thresholds for injury to vertebrae and intervertebral discs, and much less than loads on the lower back during everyday bending and lifting activities. As collision severity increased, seat backs yielded more and occupants remained in somewhat reclined positions after the impact. The lumbar compression in these tests was less than the loads in tests at lower speeds. In some high-speed rear-end crashes, the occupant’s head may contact vehicle structures behind the occupant (such as the rear seat), which increases spine compression beyond the levels measured in these tests. However, in the absence of head contact, lower-back compression in rear-end collisions is typically much less than the loads the occupant experiences during daily activities.
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