Biomechanical analysis of a new bilateral pedicle screw fixator system based on topological optimization

Abstract

Lumbar interbody fusion supplemented with a pedicle screw fixator is an effective treatment for spinal instability, but traditional bilateral pedicle screw fixator may cause some complications, such as degenerative disease of adjacent segments and stress concentration. The purpose of this study is to decrease the stiffness of the rod by using topology optimization to alleviate the above problems. The finite element models of the intact lumbar spine, lumbar spine implanted with traditional bilateral pedicle screw fixator (BPS) and a new fixator designed by using topology optimization (TOD) were developed and compared. Compared with the traditional rigid rod, the volume of TOD rod was reduced by 19.8%. The results showed that the TOD model was similar to the BPS model in terms of the range of motions. TOD reduced intradiscal pressure, stresses in intervertebral discs, and facet contact forces of the adjacent segments. The TOD model significantly decreased the stress concentration region of screws and rods and reduced the stresses in pedicle screws, rods and the junction between the vertebral bodies and screws. TOD fixator may provide a stable condition to the fusion segment as well as the BPS fixator. What’s more, TOD alleviates the adjacent segment disease and lower the risk of screw breakage, rod breakage, and vertebral damage. The new rod designed by topology optimization might also be useful in alleviating adjacent segment disease, stress concentration and stress shielding effect.