Characterization of the Lumbar Spine Dynamic Compression-Flexion Response Until Injury

The lumbar spine flexion moment-angle response with superimposed compression serves as the blueprint for spinal behavior and stiffness in the sagittal plane but has rarely been considered at large loads and deformations, particularly until the instance of injury and in dynamic environments. Response curves can also be utilized to understand population-level response and variation by developing one or more mean response curves (MRC) and corridors. The objective of this study was to characterize the individual and average lumbar spine's mechanical response in dynamic, injurious compression-flexion loading. When doing this, several factors were investigated to elucidate possible sources of human variation that would indicate the need for more than one MRC and corridor pair. The flexion moments and angles from forty postmortem human surrogate lumbar spine sections were quantified until the instance of injury. The nonlinear responses could be described by three characteristic traits: first region with low stiffness (0.9±0.6 Nm/deg) that transitioned to a second region of higher stiffness (8.5±4.1 Nm/deg) at a certain flexion bending angle (14.7±5.8 deg). The stiffness, MRCs, and corridors were largely similar across the selected factors, with a few exceptions. The outcomes from this study indicated that individually including knowledge of known donor and experimental factors resulted in a similar magnitude of human variation observed in the mechanical responses. The fundamental data on stiffness and mechanical response starting from a zero-stress state and continuing until injury occurred may be used to develop and tune other virtual and physical human surrogates.