Biomechanics of Lumbar Spine Injury in Road Barrier Collision–Finite Element Study

Pachocki, L.; Daszkiewicz, K.; Łuczkiewicz, P.; Witkowski, W. · 2021 · DOAJ

DOI: 10.3389/fbioe.2021.760498

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Summary

This study investigates the biomechanical mechanisms of lumbar spine injuries occurring during vehicle collisions with concrete road safety barriers (RSBs). While literature indicates that such crashes frequently cause vertebral fractures, the specific injury mechanism remains unclear, and current safety evaluations do not adequately address lumbar spine risks. The authors aimed to clarify how axial compression and bending moments contribute to these fractures using finite element (FE) simulations. The researchers employed a two-stage numerical modeling approach using LS-DYNA. First, a global collision model simulated a normative TB32 crash test, involving a 2014 Honda Accord impacting an H2W5B concrete barrier at 110 km/h and a 20° angle. The vehicle contained a ViVA human body model representing a 50th percentile female occupant. Kinematic data from the thoracic (Th12) and lumbar (L5) vertebrae were extracted from this global simulation and applied as boundary conditions to a detailed FE model of the lumbar spine. This detailed model was based on the THUMS v6.1 geometry but featured refined meshing and modified material properties for ligaments, nucleus pulposus, and annulus fibrosus to align with experimental data. Injury risk was assessed using the Lumbar Spine Index (LSI), minimum principal strain, Huber–von Mises–Hencky (HMH) effective stress, and a damage variable. The results demonstrated that the primary injury mechanism occurs during the vehicle’s landing phase, approximately 0.65 seconds after impact. As the vehicle landed, the occupant dropped onto the seat, generating axial compression forces of approximately 2.6 kN and significant flexion bending moments, peaking at 34.7 Nm for L2 and 37.8 Nm for L3. The LSI for the L1–L5 section reached 2.80, exceeding the fracture threshold of 2.29. Analysis of strain, stress, and damage variables identified the L2 and L3 vertebrae, along with the inferior part of L1, as the areas most prone to fracture. These findings were consistent with three specific cases retrieved from the CIREN database, which documented similar burst fractures in the L1–L3 region during RSB collisions. The study concludes that lumbar spine fractures in RSB collisions are caused by a combination of high-energy axial compression and flexion bending moments resulting from the occupant’s descent during vehicle landing. This mechanism affects the L1–L3 section primarily. The findings highlight a previously uncharacterized injury pathway that persists even without vehicle interior malfunctions, suggesting that current safety standards may overlook this risk. The authors recommend incorporating flexion moments into injury risk assessments and note that future research should expand to various impact conditions and occupant anatomies to further validate these mechanisms.

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• vru crash typology