Background and Objective

Artificial vertebral implant with a lateral or posterior screw-rod fixation system are usually employed in lumbar reconstruction surgery to rebuild the lumbar spine after partial resection due to a tumor or trauma. However, few studies have investigated the effect of the various fixation systems on the biomechanics of the reconstructed lumbar system. This study aims to evaluate the influence of different surgical fixation strategies on the biomechanical performance of a reconstructed lumbar spine system in terms of the strength and long-term stability.

Methods

Two typical lumbar spine reconstruction case models that correspond to lateral or posterior fixation systems were built based on the clinical data. Finite element analyses were performed, and comparisons were made between the two models based on the predicted stress distribution of the reconstructed lumbar spine model, bone-growth area of the endplate, and the range of motion under various normal daily activities.

Results

The load from the upper vertebral body was found to be effectively transmitted onto the lower vertebral body by a vertebral implant with the lateral fixation system; this was favorable for bone growth after surgery. However, significantly high stresses were concentrated around the interaction region between the screws and bone, owing to the uneven lateral fixation structure; this may increase the risk of bone fractures and screw loosening in the long term. For the posterior fixation case, stably posterior fixation structure was favorable to maintain stability for the reconstructed lumbar spine. However, the load was mainly transmitted via the fixation rod rather than the vertebral implant, owing to the stress shielding effect. Therefore, the predicted strain on the endplate were insufficient for bone ingrowth under most of the spinal activates, which could cause bone loss and prosthesis loosening.

Conclusions

In this study, the comparisons of the reconstructed lumbar spine system with lateral and posterior fixation strategies were conducted. The Pros and Cons of these two fixation strategies was deeply discussed and the associated clinical issues were provided. The results of this study will have a clear impact in understanding the biomechanics of the lumbar spine with different fixation strategies and providing necessary instructions to the design and application of the lumbar spinal fixation system.

中文翻译：

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椎体置换的生物力学特征：不同固定策略的影响。

背景与目的

腰椎重建手术中通常采用带有侧向或后方螺钉杆固定系统的人工椎骨植入物，以在由于肿瘤或创伤而部分切除后重建腰椎。但是，很少有研究调查各种固定系统对重建腰椎系统生物力学的影响。这项研究旨在评估强度和长期稳定性方面不同的手术固定策略对重建的腰椎系统的生物力学性能的影响。

方法

根据临床数据建立了两个对应于外侧或后固定系统的典型腰椎重建病例模型。进行了有限元分析，并根据重建的腰椎模型的预测应力分布，终板的骨生长面积以及各种正常日常活动下的运动范围，对两个模型进行了比较。

结果

发现通过带有侧向固定系统的椎骨植入物，有效地将来自上椎体的负荷传递到了下椎体上。这有利于手术后的骨骼生长。然而，由于侧向固定结构不均匀，因此应力明显集中在螺钉与骨骼之间的相互作用区域周围。从长远来看，这可能会增加骨折和螺丝松动的风险。对于后路固定病例，稳定的后路固定结构有利于维持重建腰椎的稳定性。然而，由于应力屏蔽作用，载荷主要通过固定杆而不是椎骨植入物传递。因此，在大多数脊柱活动下，终板上预计的应变不足以使骨向内生长，

结论

在这项研究中，比较了重建的腰椎系统与侧向和后向固定策略。深入讨论了这两种固定策略的利弊，并提供了相关的临床问题。这项研究的结果将对了解采用不同固定策略的腰椎生物力学产生明显影响，并为腰椎固定系统的设计和应用提供必要的指导。