Role of endplates in contributing to compression behaviors of motion segments and intervertebral discs

Schematic of rat tail demonstrating where specimens were harvested (A), and the testing setup for motion segments (B), single vertebrae (C), and disc explants (D).

Displacement data with time obtained for the full mechanical testing protocol for a typical (A) explant and (B) motion segment. Displacement point's d1, d2, d3, d4, and d5 refer to the displacement after 4h at 0.04MPa, after 4h at 0.2MPa, after 6h of recovery following the 0.2MPa load, after 4h at 1.0MPa and after 6h of recovery following the 1.0MPa load, respectively. These markers are slightly offset from data for increased visibility.

Equilibrium displacement data for motion segment, vertebrae and explants loaded to 1MPa apparent stress. Comparison demonstrates the equilibrium disc deformation is similar in the disc explant and motion segment. However motion segment undergoes large total deformations due to contributions from vertebrae and discs.

Creep data for (A) disc explant and (B) motion segment samples subjected to effective stresses of 0.2 and 1MPa. Experimental data and stretched exponential model are both shown with creep deformations given as positive in compression, with time-axis adjusted so that both 0.2 and 1MPa experiments begin at and with different y-axis scales.

Average values for the time constants from the stretched exponential fits for 0.2 and 1MPa experiments for creep (A,B) and recovery (C,D) experiments. The time constant, τ, was significantly affected by endplate permeability conditions for both creep and recovery experiments while the time constant β was insensitive to endplate permeability conditions. Note that scales are different in each sub-figure.