Biomechanics of Lumbar Motion-Segments in Dynamic
Compression 2017-22-0001
Recent epidemiology studies have reported increase in lumbar spine injuries in
frontal crashes. Whole human body finite element models (FEHBM) are frequently
used to delineate mechanisms of such injuries. However, the accuracy of these
models in mimicking the response of human spine relies on the characterization
data of the spine model. The current study set out to generate characterization
data that can be input to FEHBM lumbar spine, to obtain biofidelic responses
from the models. Twenty-five lumbar functional spinal units were tested under
compressive loading. A hydraulic testing machine was used to load the superior
ends of the specimens. A 75N load was placed on the superior PMMA to remove the
laxity in the joint and mimic the physiological load. There were three loading
sequences, namely, preconditioning, 0.5 m/s (non-injurious) and 1.0 m/s
(failure). Forces and displacements were collected using six-axis load cell and
VICON targets. In addition, acoustic signals were collected to identify the
times of failures. Finally, response corridors were generated for the two
speeds. To demonstrate the corridors, GHBMC FE model was simulated in frontal
impact condition with the default and updated lumbar stiffness. Bi-linear trend
was observed in the force versus displacement plots. In the 0.5 m/s tests, mean
toe- and linear-region stiffnesses were 0.96±0.37 and 2.44±0.92 kN/mm. In 1.0
m/s tests, the toe and linear-region stiffnesses were 1.13±0.56 and 4.6±2.5
kN/mm. Lumbar joints demonstrated 2.5 times higher stiffness in the
linear-region when the loading rate was increased by 0.5 m/s.