The mechanical stability of lumbar transpedicular dynamic stabilization (LTDS) was determined by simulating the degree to which the pedicle screws penetrated the lateral pedicle cortex. A finite element model of the L4-5 segment was established. Four states of pedicle screw implantation were simulated: in Type 1, the pedicle screw was located entirely within the pedicle; in Types 2, 3, and 4, the pedicle screw broke through the lateral pedicle cortex by ≤ 2 mm, 2.1–4 mm, and > 4 mm, respectively. The L4-5 segment was fixed with LTDS with seven pedicle screw fixation models: Groups A (all screws: Type 1), B (left screws: Type 2; right screws: Type 1), C (left screws: Type 3; right screws: Type 1), D (left screws: Type 4; right screws: Type 1), E (all screws: Type 2), F (all screws: Type 3) and G (all screws: Type 4). The corresponding mechanical indicators were recorded. Among Groups A, B, C and D, Group B had the smallest overall displacement and overall strain, followed by Groups A, B, C, and D; the overall stress and pedicle screw stress of Group D were the lowest, followed by Groups C, B, and A; and there were no significant differences in overall displacement or pedicle screw stress among the groups (p > 0.05). However, there were significant differences in overall strain and overall stress among the groups (all p 4 mm, so such penetration and should be avoided.
Zhao et al. (Mon,) studied this question.