Poster P8 - Characterization of Lumbar Acceleration in Rear-End Impacts Between Human Volunteers, Post-Mortem Human Subjects, and Anthropomorphic Test Devices

Saturday, October 26, 2024

10:00 AM - 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

KZ

Keya Zambare, n/a

Biomechanical Engineering Assistant
Biomechanical Consultants, Inc.
Davis, California, United States
Jordan Ogbu Felix

Biomechanical Engineering Assistant
Biomechanical Consultants, Inc.
Davis, United States

Co-Author(s)

KA

Kevin Adanty, PhD

Forensic Biomechanist
Biomechanical Consultants, Inc.
Davis, California, United States
SS

Sean D. Shimada, PhD (he/him/his)

President
Biomechanical Consultants, Inc.
Davis, California, United States

Introduction: Despite the low incidence of serious lumbar injuries following motor vehicle rear-end impacts, occupants often report complaints of low back pain [1]. Lumbar acceleration is an important metric for assessing injury causation and developing occupant tolerances during rear collisions [2]. Rear impact crash tests measuring lumbar acceleration have utilized three different occupant types: human volunteers, post-mortem human subjects (PMHS), and anthropomorphic test devices (ATDs). Human volunteers best reflect acceleration in real crash scenarios but are limited to low severity impacts due to ethical considerations [3]. PMHS can be employed in higher speed impacts but lack muscular input, which may be an important contributor to occupant acceleration [4]. ATD models provide consistency and repeatability in trials, but anatomically differ in their representation of the human lumbar spine. The Hybrid III is the most widely used ATD but has a relatively simple lumbar spine [5] compared to the BioRID II, which features flexible lumbar spinal structures modeled analogous to human lumbar vertebrae [6-7]. Based on these physiological differences between the occupant types, there may be corresponding differences in lumbar spine acceleration that have not been quantified. The purpose of this study is to examine current literature and compare the distribution of reported lumbar acceleration data between occupant types in rear-end testing. This study will be relevant for biomechanical and safety experts to establish potential differences between occupant types, and critically assess how well PMHS and ATDs reproduce human lumbar acceleration.

Materials and

Methods: The current literature was reviewed to identify rear-end sled crash tests or vehicle-to-vehicle collisions reporting peak longitudinal lumbar acceleration. Studies using belted volunteer, PMHS, and ATD occupants seated in the driver seat were included in the analysis. Additionally, studies were included if occupant instrumentation was placed between the T12 and S1 vertebral regions, internally or externally. The X-axis was standardized to be positive in the forward direction for all tests. Lumbar acceleration maxima from each crash test were recorded and plotted against the vehicle’s or sled’s peak longitudinal change in velocity (ΔV). Numerical data not explicitly stated in the studies were extracted from plots using a web-based imaging tool [8].

Results, Conclusions, and Discussions: The review of the literature revealed five studies reporting lumbar acceleration data from rear-end impacts for human volunteers (n=3), PMHS (n=1), and BioRID IIg ATDs (n=1). No studies using Hybrid III ATDs reported lumbar acceleration. Present literature indicates that lumbar acceleration was less frequently reported in PMHS and ATDs compared to human volunteers. ATD studies examining lumbar response metrics primarily reported lumbar loads and moments [5, 9-26].

Peak longitudinal lumbar acceleration analysis showed that volunteer lumbar acceleration ranged from 0.80-6.08g [27-29]. This contrasts with PMHS lumbar accelerations of 3.80-4.20g [30] and BioRID IIg ATD lumbar accelerations of 0.87-15.70g [31]. The ATD data displayed a wider lumbar acceleration range than the volunteer and PMHS data, with a notable gap from 1.40-5.20g (Figure 1).

A factor contributing to this discrepancy is that crash tests with each occupant type were performed within different ΔV ranges. Crash tests with PMHS and ATD occupants were performed at ΔVs of 13.00 and 16.00 km/h, respectively. In contrast, volunteer crash tests had a maximum ΔV of only 10.20 km/h (Figure 2). The lack of volunteer data past 10.20 km/h precludes data extrapolation at higher ΔV, preventing effective comparison of lumbar acceleration across different occupant types. As a result, the effectiveness of PMHS and ATDs in capturing the human lumbar acceleration response at lower ΔVs cannot be assessed.

This analysis contributes to present research on the lumbar spine response during rear-end collisions. Current crash tests document human volunteer lumbar acceleration at ΔVs below 10.20 km/h, whereas PMHS and ATD lumbar acceleration are only reported at higher ΔVs. Therefore, the authors cannot establish at this time if PMHS and ATD occupants accurately represent real-life lumbar acceleration in low-speed rear-end impacts based on prior published literature. Future work could derive lumbar acceleration from ATD loads through inverse dynamics and conduct crash tests at lower ΔVs to enable a critical assessment on how well PMHS and ATD occupants capture lumbar acceleration in low-speed rear-end collisions. Furthermore, with additional PMHS and ATD crash testing at lower ΔVs, data in Figure 2 can be expanded to create useful predictive models for forensic biomechanists.

Acknowledgements (Optional):