Comparative Three-Dimensional Finite Element Analysis of 4 Kinds of Pedicle Screw Schemes for Treatment of Adult Degenerative Scoliosis

BACKGROUND: This study aimed to evaluate the biomechanical stress of the internal fixation screws and vertebral bodies after the full-segment, interval, key vertebral, and strategy pedicle screw fixations under 7 work conditions in a patient with adult degenerative scoliosis (ADS) using finite elements (FE) analysis. MATERIAL/METHODS: A patient with ADS underwent internal fixation by pedicle screws after posterior incision in combination with subtotal laminectomy decompression and bone graft fusion, and received thin-layer computed tomography (CT) spine scanning at T12–L5. The CT data were used to constitute three-dimensional FE full-segment, interval, key vertebral, and strategic pedicle screw models. The stress of each screw-rod system under different working conditions was evaluated. RESULTS: Forward flexion, backward extension, lateral flexion, and rotation greatly increased the force of the pedicle screw systems. The maximum stress of the screw-rods was the lowest in the full-segment model under almost all the working conditions except for the upright situation. The maximum stress of the vertebral bodies was the minimum in the strategic model under all the 7 working conditions, followed by that in the key vertebra and full-segment models. CONCLUSIONS: Collectively, the strategic and key vertebra pedicle screw schemes can decrease the biomechanical stress of screw-rod systems and vertebral bodies, which is close to the full-segment scheme. Our results may help explore the optimal surgical means for pedicle screw fixation for ADS patients, which can maximally reduce the risk of screws-related postoperative complications and simultaneously maintain a reasonable 3D orthopedic effect.