Static and dynamic biomechanical responses of the lumbar spine under different loads: A finite element study

Lumbar spinal loads differ across various scenarios, including lumbar extension in the lateral recumbent position, seated/standing trunk extension, upright sitting or standing, muscular tension, muscular relaxation, and whole-body vibration. Nevertheless, systematic comparative studies concerning lumbar biomechanical behaviors under these diverse scenarios remain scarce. To provide guidance and references for clinical biomechanics and simulation studies, this study adopts a validated lumbar-pelvic (L3-P) finite element model to investigate the biomechanical characteristics of the lumbar spine under various loading conditions. The maximum von Mises stress in the annulus fibrosus was located at the L5-S1 intervertebral disc under moment and follower-load conditions, whereas the maximum stress occurred at the L4-L5 intervertebral disc under gravity conditions. The maximum pressure in the nucleus pulposus consistently appeared at the L3-L4 segment under all applied loads. The facet joint contact force increased toward the lower lumbar spine. The loading sequence affected the transient process rather than the final results. Under whole-body vibration, the relaxed posture led to higher lumbar spinal loads and stresses, whereas a tensed muscular state reduced such loads and stresses. Therefore, appropriate loading conditions should be selected according to lumbar spinal status in clinical practice and simulation studies to achieve accurate evaluation and analysis.