Purpose

Analyze the biomechanical effect of postero-lateral instrumentation with and without posterior bone graft as well as effect of consolidation of the graft. Study objectives are (1) whether bone graft alone will provide enough additional strength to the weakened spine, (2) how the addition of posterior bone graft help in extending the life of the fusion construct, and (3) compare the effect of gradual consolidation of the bone-graft on the spine biomechanics.

Methods

A lumbar spine finite element model was used to analyze the effects of bone-graft alone and varying grades of bone-graft consolidation with postero-lateral instrumentation on spine biomechanics. The spine stiffness and stresses in the posterior rods and screws were determined for moments applied in the three physiological directions in addition to pre-load.

Results

Stiffness of a normal lumbar spine with a solid consolidated posterior bone graft was found to be 10 times that of an intact lumbar spine. Posterior instrumentation further increased the spine stiffness by 20 fold. A 50% solid consolidation of the graft reduced the screw-rod maximum von-Mises stress by 45% and a 65% reduction in screw-rod stress was calculated with completely fused graft.

Conclusion

A fused graft with posterior instrumentation provided a 200 fold increase in stiffness of an intact spine while producing stress shielding to the Ti rod-screw system. Considerable reduction of the maximum von-Mises stresses in the postero-lateral rod and screw fusion system (65%) will contribute to prevention of implant failure under repetitive loading highlighting the importance of consolidation of posterior bone-graft.

中文翻译：

---

腰椎手术中的后骨移植可减轻螺杆系统中的压力-有限元研究。

目的

分析有或没有后植骨的后外侧器械的生物力学效果以及植骨固结的效果。研究目标是（1）单独的骨移植是否会为弱化的脊柱提供足够的额外强度；（2）后部骨移植的添加如何帮助延长融合结构的寿命；以及（3）比较逐渐巩固的效果植骨对脊柱生物力学的影响。

方法

腰椎有限元模型用于分析单独的骨移植以及后外侧器械对不同等级的骨移植固结的影响，以评估脊柱的生物力学。除了预先加载外，还确定了在三个生理方向上施加的力矩下后杆和螺钉中的脊柱刚度和应力。

结果

发现具有坚固的后路坚固骨移植的正常腰椎的刚度是完整腰椎的10倍。后置器械进一步使脊柱刚度增加了20倍。移植物的50％固结固结使螺杆最大von-Mises应力降低了45％，对于完全熔融的移植物，螺杆应力降低了65％。

结论

带有后置器械的融合移植物使完整脊柱的刚度提高了200倍，同时对钛棒-螺钉系统产生了应力屏蔽。后外侧杆和螺钉融合系统中最大von-Mises应力的显着降低（65％）将有助于防止在重复载荷下植入失败，突出了巩固后路植骨的重要性。