Assessment of risk factors affecting mechanical stress on the adjacent segments after lumbar fusion

Abstract

[한글]

[영문]Introduction. The ablation of proximal posterior ligament complex (PLC) continuity and the presence of pedicle screws have been reported to affect the biomechanics at adjacent segments after lumbar fusion. However, there have been few studies regarding the quantitative assessment of their contribution to overstress at adjacent segments after lumbar fusion. Therefore, the purpose of this study is to investigate the changes in the disc stress and range of motion (ROM) at adjacent segments after lumbar fusion based on the presence of pedicle screws or the preservation of the proximal PLC.Methods. In the validated intact lumbar finite element model including L2 through L5, four types of L3-4 fusion models were simulated. These models included the preservation of the PLC continuity with pedicle screws (Pp WiP), the preservation of PLC continuity without pedicle screws (Pp WoP), the sacrifice of PLC with pedicle screws (Sp WiP), and the sacrifice of PLC without pedicle screws (Sp WoP). In each scenario, the ROM and maximal von Mises stress of discs at adjacent segments were analyzed under 4 pure moments.Results. Among the 4 models, the Sp WiP yielded the greatest increase in the ROM and the maximal von Mises stress of the disc at adjacent segments under four moments. Following the SP WiP, the order of increase of the ROM and the disc stress was Pp WiP, Sp WoP, and Pp WoP. Furthermore, the increase of ROM and disc stress at the proximal adjacent segment was more than at the distal adjacent segment under all 4 moments in each model.Conclusions. The current study suggests that the preservation of the PLC continuity or the removal of pedicle screws after complete fusion could decrease the stress at adjacent segments, and their combination could act synergistically.