Although most of the research on vehicular rear impacts has focused on the neck, there is increasing current concern about the lumbar spine. Spinal bending superimposed with sudden spinal compression has been suggested as a mechanism of creating acute herniations on the rare occasion in which low back pain associated with an intervertebral disc herniation was reported. During automotive rear-impacts, the vehicle accelerations are directed anteriorly, and the seat backs deflect posteriorly. In vehicle seats equipped with floor-mounted seatbelt restraints, the pelvis is restrained by the seatback and seatbelt, while the torso ramps upward and rearward on the seatback during the rearward motion, producing tension in the lumbar spine. However, in an all-belts-to-seat arrangement, the lumbar spines may experience overall compressive and bending loads. With either seatbelt arrangement, the spine might experience some transient bending and compression, which could be consistent with the proposed mechanism of acute disc herniation.
This paper explored spinal bending and loading during rear impacts with changes of velocity (delta Vs) of 2.2, 3.6, 5.4, and 6.7 m/s (5, 8, 12, 15 mph), using Hybrid III and BioRID II anthropomorphic test devices (ATDs). Male 50
th
-percentile ATDs of both types were seated side-by-side on a pneumatic test sled and restrained with 3-point belts. One test at each speed was run using floor-mounted restraints (Ford Taurus 2002-2003), and one test each was run at 2.2 m/s and 5.4 m/s delta Vs using an all-belts-to-seat configuration (2001 Chevrolet Suburban). Lumbar forces and moments were measured using the two types of ATDs. High-speed videos were used to grossly assess ATD motion patterns. The overall results were compared to the literature to determine if the ATD lumbar spines in our tests experienced loads compatible with the creation of acute disc herniations and protrusions during low to moderate speed rear impacts.