Dong Enchun, Shi Lei, Kang Jianfeng, Li Dichen, Liu Bin, Guo Zheng, Wang Ling, Li Xiangdong
State Key Laboratory for Manufacturing System Engineering, Xi'an Jiaotong University, Xi'an, 710054, Shaanxi, China.
Department of Orthopedics, Xijing Hospital, The Fourth Military Medical University, Xi'an, 710032, Shaanxi, China.
Comput Methods Programs Biomed. 2020 Dec;197:105741. doi: 10.1016/j.cmpb.2020.105741. Epub 2020 Sep 8.
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.
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.
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.
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.
在腰椎重建手术中，通常采用带有侧方或后方螺钉-棒固定系统的人工椎体植入物，用于因肿瘤或创伤导致部分切除后重建腰椎。然而，很少有研究探讨各种固定系统对重建腰椎系统生物力学的影响。本研究旨在从强度和长期稳定性方面评估不同手术固定策略对重建腰椎系统生物力学性能的影响。
基于临床数据构建了对应侧方或后方固定系统的两种典型腰椎重建病例模型。进行了有限元分析，并根据重建腰椎模型的预测应力分布、终板骨生长区域以及各种日常活动下的运动范围，对两种模型进行了比较。
发现采用侧方固定系统的椎体植入物能有效地将来自上位椎体的载荷传递到下位椎体；这有利于术后骨生长。然而，由于侧方固定结构不均匀，螺钉与骨之间的相互作用区域周围应力显著集中；从长远来看，这可能增加骨折和螺钉松动的风险。对于后方固定情况，稳定的后方固定结构有利于维持重建腰椎的稳定性。然而，由于应力遮挡效应，载荷主要通过固定棒而非椎体植入物传递。因此，在大多数脊柱活动下，终板上预测的应变不足以促进骨长入，这可能导致骨质流失和假体松动。
本研究对采用侧方和后方固定策略的重建腰椎系统进行了比较。深入讨论了这两种固定策略的优缺点，并提出了相关的临床问题。本研究结果将对理解不同固定策略下腰椎的生物力学以及为腰椎固定系统的设计和应用提供必要指导产生明显影响。
