In this study some 3D nonlinear finite element models of the intact ligamentous lumbar units were constructed. The analysis accounts for both material and geometric nonliniearities. Two commercial types of pedicle screw systems were used to simulate the stabilizing process. Load-displacement behavior of the stabilized models and stress distribution in various spinal structures were compared with those of intact models. In addition, a parametric stabilized model was developed to evaluate the effects of variation in material properties of the graft and cancellous bone, pedicle morphometry and position of the graft on the results. Stress distribution in the implants was also investigated as a function of variation in insertion technique to determine how the risk of pedicle screw breakage is affected by changes in screw insertion depth, height and angle within the pedicle. Results of parametric model indicated that pedicle morphometry has a minor effect on the stresses in the pedicle screw while these stresses can strongly affected by surgical technique.
F. Farahmand , H. Hosseini Nasab
