| Significant effort has been invested in developing finite element models in the field of spinal biomechanics. However, nearly all previous studies have applied artificially set static or short duration dynamic loads (<1 second) to a single motion segment, while most low back disorders found in industry today are due to tasks that are repetitive in nature. Accordingly, the purpose of this study was to develop a model of the complete lumbar spine capable of determining the response to realistic repetitive motion.; A new finite element model of the lumbar spine was developed that considers nonlinear material and geometric behavior, including large displacements and rotations. The model was interfaced with an EMG-assisted free-dynamic model which provides subject specific motion data for use as partial input to the finite element model. The initial geometry of the lumbar spine is a crucial part of the input, and a new method for determining the neutral posture geometry using an external goniometer was developed and validated. Validation and sensitivity analyses were also performed on both the individual model components and the complete model. In addition, the model response, including stresses, deformations, and energy dissipation, for up to twenty minutes of continuous, measured repetitive sagittally-symmetric flexion was calculated. Furthermore, the dynamic creep and energy dissipation at all intervertebral discs levels was determined for 8 hours of cyclic loading.; The model developed in this study is able to simulate large displacement, dynamic, cyclic behavior using realistic motions through linking to human subject experiments. Larger forces, creep, and energy dissipation were predicted at the lower lumbar spine levels, and the maximum stresses and energy dissipation were found to be highly dependent upon the bending motion, not only the axial compression. In addition, higher lifting frequencies and velocities lead to increased creep and energy dissipation, with velocity having a larger effect. Subject specificity, including the initial lumbar spine geometry and motion during flexion were found to have an important effect on the resulting spinal loads. The results suggest that the new model is a valid approach to assessing the effect of repetitive motion on the lumbar spine. |
