Biomechanical characterization of bilateral pedicle screw internal fixation combinations on lumbar vertebrae

Purpose Pedicle screw fixation has been considered a suitable surgical intervention for addressing a diverse range of indications involving the lumbar spinal segments, but the impact of bilateral pedicle screw internal fixation combinations on the stability and flexibility of vertebral body motion has been limited. This study aimed to the effect of pedicle screw internal fixation on the mechanical characterization of lumbar multi-segmental vertebra under various loading conditions. Methods Porcine lumbar multi-segmental vertebral samples were tested with three pedicle screw fixation groups including rigid fixation, mixed fixation and dynamic fixation under four loading conditions of flexion, posterior extension, left-side bend, and right-side bend at bending moments of 3 N⋅m, 4 N⋅m, 5 N⋅m and 6 N⋅m, respectively. The stability and flexibility of the segmental motion were statistically analysed. Results The flexibility of joint activities increased using one-way dynamic pedicle screws with the range of motion for mixed fixation and dynamic fixation increased by 30% and 47% in left side bend and by 25% and 73% in right side bend, respectively. The range of motion for lumbar vertebra increased with higher moments. Conclusions The flexibility of joint activities was improved using one-way dynamic pedicle screws and the mixed fixation was considered moderate providing larger flexibility in right and left side bend without compromising stabilization. The results of this study are useful for providing theoretical reference for clinical selection of surgical plans.