BACKGROUND Adjacent segment disease (ASD) is a common complication after posterior lumbar interbody fusion (PLIF). Recently, a topping-off surgery (non-fusion with Coflex) has been developed to reduce the risk of ASD, yet whether and how the topping-off surgery can relieve ASD remains unclear. The purpose of this study was to explore the biomechanical effect of PLIF and Coflex on the adjacent segments via finite element (FE) analysis and discuss the efficacy of Coflex in preventing ASD. METHODS A FE model of L3-L5 segments was generated based on the CT of a healthy volunteer via three commercially available software. Coflex and PLIF devices were modeled and implanted together with the segment model in the FE software. In the FE model, a pre-compressive load of 500 N, equal to two-thirds of the human body mass, was applied on the top surface of the L3. In addition, four types of moments (anteflexion, rear protraction, bending, and axial rotation) set as 10 Nm were successively applied to the FE model combined with this pre-compressive load. Then, the range of motion (ROM), the torsional rigidity, and the maximum von Mises equivalent stress on the L3-L4 intervertebral disc and the implant were analyzed. RESULTS Both Coflex and PLIF reduced ROM. However, no significant difference was found in the maximum von Mises equivalent stress of adjacent segment disc between the two devices. Interestingly enough, both systems increased the torsional rigidity at the adjacent lumbar segment, and PLIF had a more significant increase. The Coflex implant had a larger maximum von Mises equivalent stress. CONCLUSIONS Both Coflex and PLIF reduced ROM at L3-L4, and thus improved the lumbar stability. Under the same load, both devices had almost the same maximum von Mises equivalent stress as the normal model on the adjacent intervertebral disc. But it is worthy to notice the torsional rigidity of PLIF was higher than that of Coflex, indicating that the lumbar treated with PLIF undertook a larger load to reach ROM of Coflex. Therefore, we presumed that ADS was related to a higher torsional rigidity.

中文翻译：

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退变性手术与后路腰椎椎间融合术治疗退行性腰椎疾病：有限元分析。

背景技术邻近节段疾病（ASD）是后路腰椎椎间融合术（PLIF）后的常见并发症。近来，已经开发出一种顶开手术（不与Coflex融合术）以降低ASD的风险，但是还不清楚该顶开手术是否以及如何能够缓解ASD。这项研究的目的是通过有限元（FE）分析探索PLIF和Coflex对相邻节段的生物力学作用，并讨论Coflex预防ASD的功效。方法基于健康志愿者的CT，通过三种市售软件生成L3-L5节段的FE模型。对Coflex和PLIF设备进行建模，并将其与段模型一起植入FE软件中。在有限元模型中，预压缩载荷为500 N，等于人体质量的三分之二，在L3的顶部表面上使用。此外，与该预压缩载荷相结合，依次将设置为10 Nm的四种力矩（前屈，后伸，弯曲和轴向旋转）应用于有限元模型。然后，分析了L3-L4椎间盘和植入物的运动范围（ROM），扭转刚度以及最大冯·米塞斯等效应力。结果Coflex和PLIF都减少了ROM。但是，在两个设备之间，相邻段盘的最大冯·米塞斯等效应力没有发现显着差异。有趣的是，两个系统都增加了相邻腰段的抗扭刚度，而PLIF的增加幅度更大。Coflex植入物具有更大的最大冯·米塞斯等效应力。结论Coflex和PLIF都降低了L3-L4处的ROM，从而提高了腰椎稳定性。在相同的负载下，两个设备的最大冯·米塞斯等效应力与相邻椎间盘上的正常模型几乎相同。但值得一提的是，PLIF的抗扭刚度高于Coflex，表明用PLIF治疗的腰椎承受了更大的负荷以达到Coflex的ROM。因此，我们认为ADS与较高的扭转刚度有关。