Multiobjective Optimization Design of Spinal Pedicle Screws Using Neural Networks and Genetic Algorithm: Mathematical Models and Mechanical Validation

Short-segment instrumentation for spine fractures is threatened by relatively high failure rates. Failure of the spinal pedicle screws including breakage and loosening may jeopardize the fixation integrity and lead to treatment failure. Two important design objectives, bending strength and pullout strength, may conflict with each other and warrant a multiobjective optimization study. In the present study using the three-dimensional finite element (FE) analytical results based on an L25 orthogonal array, bending and pullout objective functions were developed by an artificial neural network (ANN) algorithm, and the trade-off solutions known as Pareto optima were explored by a genetic algorithm (GA). The results showed that the knee solutions of the Pareto fronts with both high bending and pullout strength ranged from 92% to 94% of their maxima, respectively. In mechanical validation, the results of mathematical analyses were closely related to those of experimental tests with a correlation coefficient of −0.91 for bending and 0.93 for pullout (P<0.01 for both). The optimal design had significantly higher fatigue life (P<0.01) and comparable pullout strength as compared with commercial screws. Multiobjective optimization study of spinal pedicle screws using the hybrid of ANN and GA could achieve an ideal with high bending and pullout performances simultaneously

Fixation and fusion

Spinal fixation represents the gold standard for the surgical treatment of a variety of diseases, including degenerative conditions, deformities, traumas, and tumors. The overall aims are to stop the degenerative process, to provide pain relief through stabilization, and often to promote a solid bony fusion. Fixation and fusion can be achieved by using a variety of approaches and devices, and understanding and managing the biomechanics behind each technique are crucial in determining a clinical treatment’s outcome. This chapter is divided into three sections that deal with pedicle screw fixation, posterolateral fusion, and fusion with intervertebral cages and bone grafts, in that order. In each section, the surgical technique is initially introduced with an explanation of its advantages and their clinical implications; an in-depth description of its biomechanical consequences follows with a discussion of each approach’s effect on spinal stability, kinematics, and load sharing. The state-of-the-art treatments are reviewed to provide a solid basis for understanding how the field of biomechanics is involved in the surgical treatments of degenerative disorders