Department of Bioengineering, Engineering Center for Orthopaedic Research Excellence, The University of Toledo, 2801 West Bancroft St, Toledo, OH 43606, USA.
Spine J. 2011 Aug;11(8):766-76. doi: 10.1016/j.spinee.2011.06.008. Epub 2011 Jul 29.
Wear simulators and their corresponding wear predictive models provide limited information on wear characteristics of artificial discs. Analyses in previous studies that controlled loading profiles according to International Standards Organization (ISO)/American Society for Testing and Materials standards did not account for factors such as the influence of anatomic structures. Retrieval analyses reveal failure modes that are not observed in benchtop simulations and thus indicate deficiencies associated with existing approaches.
To understand the impact of the adjoining spinal structures of a ligamentous segment on the wear of an artificial cervical disc.
Prediction of wear in artificial disc implants (total disc replacement [TDR]) in situ using finite element modeling.
A novel predictive finite element model was used to evaluate wear in a simulated functional spinal unit (FSU). A predictive finite element wear model of the disc alone (TDR Only) was developed, along the lines of that proposed in the literature. This model was then incorporated into a ligamentous C5-C6 finite element model (TDR+FSU). Both of these models were subjected to a motion profile (rotation about three axes) with varying preloads of 50 to150 N at 1 Hz, consistent with ISO 18192. A subroutine based on Archard law simulated abrasive wear on the polymeric core up to 10 million cycles. The TDR+FSU model was further modified to simulate facetectomy, sequential addition of ligaments, and compressive load; simulations were repeated for 10 million cycles.
The predicted wear patterns in the isolated disc (TDR Only) and in TDR+FSU were completely inconsistent. The TDR+FSU model predicted localized wear in certain regions, in contrast to the uniformly distributed wear pattern of the TDR-only model. In addition, the cumulative volumetric wear for the TDR-only model was 10 times that of the TDR+FSU model. The TDR+FSU model also revealed a separation at the articulating interface during extension and lateral bending. After facetectomy, the wear pattern remained lopsided, but linear wear increased eightfold, whereas volumetric wear almost tripled. This was accompanied by a reduction in observed liftoff. The addition of anterior longitudinal ligament/posterior longitudinal ligament did not affect volumetric or linear wear. On the removal of all ligaments and facet forces, and replacement of follower load with a compressive load, the wear pattern returned to an approximation of the TDR-only test case, whereas the cumulative volumetric wear became nearly equivalent. In this case, the liftoff phenomenon was absent.
Anatomic structures and follower load mitigate the wear of an artificial disc. The proposed model (TDR+FSU) would enable further study of the effects of clinical parameters (eg, surgical variables, different loading profiles, different disc designs, and bone quality) on wear in these implants.
磨损模拟器及其相应的磨损预测模型仅提供了有关人工椎间盘磨损特征的有限信息。根据国际标准化组织（ISO）/美国材料与试验协会标准进行加载分析的先前研究并未考虑解剖结构的影响等因素。检索分析揭示了在台式模拟中未观察到的失效模式，从而表明与现有方法相关的缺陷。
了解韧带节段毗邻脊柱结构对人工颈椎间盘磨损的影响。
使用有限元建模预测原位人工椎间盘植入物（全椎间盘置换术 [TDR]）的磨损。
使用新型预测有限元模型评估模拟功能脊柱单元（FSU）中的磨损。沿着文献中提出的方法，开发了单独的椎间盘（TDR 仅）的预测有限元磨损模型。然后，将该模型纳入 C5-C6 韧带有限元模型（TDR+FSU）中。这两个模型都受到旋转三个轴的运动轮廓（以 1 Hz 的 50 至 150 N 的不同预载）的影响，符合 ISO 18192。基于 Archard 定律的子程序模拟了聚合物核心的磨料磨损，达到 1000 万次循环。进一步修改 TDR+FSU 模型以模拟小关节切除、连续添加韧带和压缩载荷；模拟重复 1000 万次循环。
孤立椎间盘（TDR 仅）和 TDR+FSU 的预测磨损模式完全不一致。与 TDR 仅模型的均匀分布磨损模式相比，TDR+FSU 模型预测了某些区域的局部磨损。此外，TDR 仅模型的累积体积磨损是 TDR+FSU 模型的 10 倍。TDR+FSU 模型还显示在伸展和侧向弯曲时在关节界面处分离。小关节切除后，磨损模式仍然不均匀，但线性磨损增加了 8 倍，而体积磨损几乎增加了两倍。这伴随着观察到的抬起现象减少。前纵韧带/后纵韧带的添加不会影响体积或线性磨损。当去除所有韧带和小关节力，并将跟随力替换为压缩力时，磨损模式恢复到 TDR 仅测试用例的近似值，而累积体积磨损变得几乎相等。在这种情况下，不存在抬起现象。
解剖结构和跟随力减轻了人工椎间盘的磨损。所提出的模型（TDR+FSU）将能够进一步研究临床参数（例如手术变量、不同的加载情况、不同的椎间盘设计和骨质量）对这些植入物磨损的影响。
