To assess the biomechanical stability of tri-cortical pedicle screw fixation in adult thoracic vertebra using finite element analysis and to compare its performance with traditional fixation methods. A three-dimensional finite element model of T5-11 thoracic vertebrae was established based on CT data from a healthy adult volunteer. Four different fixation groups were designed: Group A (Short-segment pedicle screw fixation from T7 to T10), Group B (Long-segment pedicle screw fixation from T6 to T10), Group C (Short-segment pedicle screw fixation with a tri-cortical pedicle screw at T7), and Group D (Short-segment pedicle screw fixation with two tri-cortical pedicle screws at T7 and T8). Biomechanical analysis was performed under six physiological loading conditions (flexion, extension, left/right rotation, left/right lateral bending) with 8 Nm moment and 400 N axial preload. Groups C and D with tri-cortical pedicle screw fixation demonstrated numerically lower displacement compared to traditional fixation groups (A and B) under all loading conditions. The displacement in Group C decreased by 11.11%-31.47% and in Group D by 12.96%-32.34% compared to Group A across all loading conditions. Group D showed slightly better performance than Group C in displacement. Stress analysis revealed substantial reductions in adjacent segment stress (annulus fibrosus, nucleus pulposus, and cartilage endplate) in tri-cortical groups, with decreases ranging from 59.25% to 95.46% compared to Group A. Minimal difference was observed in internal fixation stress between groups. Tri-cortical pedicle screw fixation provides superior biomechanical stability in thoracic vertebra compared to traditional fixation methods, with numerically lower adjacent segment stress, suggesting potential benefits for reducing the biomechanical risk factors of proximal junctional kyphosis in clinical applications. This study provides biomechanical evidence supporting the use of tri-cortical pedicle screw fixation as a novel strategy for reducing the risk of proximal junctional kyphosis in adult spinal deformity surgery.
Sun et al. (Thu,) studied this question.