Assessment of Compressive Thoracolumbar Injury Potential and Influence of Seat Cushions on Vertical Impact Loading of a Seated Occupant

Thoracolumbar vertebral fractures are most commonly due to compressive loading modes and associated with falls from height. Two injury metrics are generally referenced for assessing the potential for compressive thoracolumbar injury; the Dynamic Response Index (DRI) and the compressive load measured between the pelvis and lumbar spine using the Code of Federal Regulations (CFR) title 49 part 572 subpart B anthropomorphic test device (ATD).

This study utilizes an ATD to investigate the injury mitigation potential of a variety of seat cushions during vertical impact in an unrestrained seated posture. ATD responses and DRI are reported for 65 vertical impacts with and without cushions from heights between 4 and 80 inches. The cushions investigated reduced ATD peak pelvic acceleration 63 +/− 11% and compressive lumbar load 42 +/− 9% on average. Results indicate a drop height of approximately 19 inches onto a rigid surface will generate ATD lumbar loads of 1500 lbs, whereas drop heights of 42 +/− 10 inches were required to produce equivalent lumbar loads with a cushion present. Conversely, the presence of a cushion had little or no influence on the resulting DRI. A 40 inch drop onto a rigid surface resulted in a DRI of 20.3 and drops of 40 inches onto a cushion resulted in DRI of 20.5 +/− 1.3. ATD lumbar load is a superior tool for qualitative comparative purposes. Neither metric has been correlated to human tolerance during unrestrained vertical impacts. Further research is required to better define their relationships to injury potential.