Moment–rotation responses of the human lumbosacral spinal column

The objective of this study was to test the hypothesis that the human lumbosacral joint behaves differently from L1–L5 joints and provides primary moment–rotation responses under pure moment flexion and extension and left and right lateral bending on a level-by-level basis. In addition, range of motion (ROM) and stiffness data were extracted from the moment–rotation responses. Ten T12–S1 column specimens with ages ranging from 27 to 68 years (mean: 50.6±13.2) were tested at a load level of 4.0 N m. Nonlinear flexion and extension and left and right lateral bending moment–rotation responses at each spinal level are reported in the form of a logarithmic function. The mean ROM was the greatest at the L5–S1 level under flexion (7.37±3.69°) and extension (4.62±2.56°) and at the L3–L4 level under lateral bending (4.04±1.11°). The mean ROM was the least at the L1–L2 level under flexion (2.42±0.90°), L2–L3 level under extension (1.58±0.63°), and L1–L2 level under lateral bending (2.50±0.75°). The present study proved the hypothesis that L5–S1 motions are significantly greater than L1–L5 motions under flexion and extension loadings, but the hypothesis was found to be untrue under the lateral bending mode. These experimental data are useful in the improved validation of FE models, which will increase the confidence of stress analysis and other modeling applications.