The use of a pedicle screw fixation system with rods made of more compliant materials has become increasingly popular for spine fusion surgery in recent years. The aim of this study was to compare stress responses of the implants in transforaminal lumbar interbody fusion (TLIF) when using flexible and conventional rigid posterior fixation systems. A previously validated intact L1–S1 finite element model was modified to simulate single-level (L4–L5) TLIF with bilateral pedicle screw fixation using two types of connecting rod (rigid and flexible rods). The von Mises stresses in the implants (including TLIF cage, pedicle screws and rods) for the rigid and flexible fixations were analyzed under static and vibration loadings. The results showed that compared with the rigid fixation, the use of flexible fixation decreased the maximum stress in the pedicle screws, but increased the maximum stress in the cage and the ratio of maximum stress in the rods to the yield stress. It was also found that with decreasing diameter of the flexible rod (i.e. increasing flexibility of the rod), the maximum stress was decreased in the pedicle screws but increased in the cage and the rods. The findings imply that compared with the rigid rod, application of the flexible rod in the pedicle screw fixation system for the TLIF might decrease the breakage risk of pedicle screws but increase the risk of cage subsidence and rod breakage. Moreover, flexibility of the rod in the flexible fixation system should be carefully determined.

近年来，将椎弓根螺钉固定系统与由更柔顺的材料制成的杆一起使用已经在脊柱融合手术中变得越来越流行。这项研究的目的是比较使用柔性和常规刚性后路固定系统时经椎间孔腰椎椎体间融合术（TLIF）植入物的应力反应。修改了先前已验证的完整L1-S1有限元模型，以使用两种类型的连杆（刚性杆和柔性杆）通过双侧椎弓根螺钉固定来模拟单级（L4-L5）TLIF。分析了静态和振动载荷下刚性和柔性固定的植入物（包括TLIF笼，椎弓根螺钉和杆）中的von Mises应力。结果表明，与刚性固定相比，柔性固定的使用降低了椎弓根螺钉的最大应力，但增加了保持架中的最大应力以及杆中的最大应力与屈服应力之比。还发现，随着挠性杆直径的减小（即，杆的挠性的增加），椎弓根螺钉中的最大应力减小，而保持架和杆中的最大应力增大。研究结果表明，与刚性杆相比，在TLIF椎弓根螺钉固定系统中应用柔性杆可能会降低椎弓根螺钉的断裂风险，但会增加保持架下陷和杆断裂的风险。此外，应仔细确定杆在柔性固定系统中的柔性。还发现，随着挠性杆直径的减小（即，杆的挠性的增加），椎弓根螺钉中的最大应力减小，而保持架和杆中的最大应力增大。研究结果表明，与刚性杆相比，在TLIF椎弓根螺钉固定系统中应用柔性杆可能会降低椎弓根螺钉的断裂风险，但会增加保持架下陷和杆断裂的风险。此外，应仔细确定杆在柔性固定系统中的柔性。还发现，随着挠性杆直径的减小（即，杆的挠性的增加），椎弓根螺钉中的最大应力减小，而保持架和杆中的最大应力增大。研究结果表明，与刚性杆相比，在TLIF椎弓根螺钉固定系统中应用柔性杆可能会降低椎弓根螺钉的断裂风险，但会增加保持架下陷和杆断裂的风险。此外，应仔细确定杆在柔性固定系统中的柔性。在TLIF的椎弓根螺钉固定系统中使用柔性杆可能会降低椎弓根螺钉的断裂风险，但会增加保持架下陷和杆断裂的风险。此外，应仔细确定杆在柔性固定系统中的柔性。在TLIF的椎弓根螺钉固定系统中使用柔性杆可能会降低椎弓根螺钉的断裂风险，但会增加保持架下陷和杆断裂的风险。此外，应仔细确定杆在柔性固定系统中的柔性。