Department of Orthopedic Surgery, College of Medicine, Seoul National University, SMG-SNU Boramae Medical Center, Korea; Institute of Medical and Biological Engineering, Medical Research Center, Seoul National University, Seoul, Korea.
Artif Organs. 2013 Nov;37(11):1014-20. doi: 10.1111/aor.12107. Epub 2013 Jul 30.
Intervertebral disc spacers using bioactive ceramics have been used to treat degenerative spinal disease. Tooth-shaped spacers are commonly used to prevent migration, but there is a possibility of fracture when inserted or after insertion. Intervertebral disc spacers with either an isosceles triangle-shaped tooth (T1) or a right triangle-shaped tooth (T2) were used as a control group. The design factors for the experimental group were modified to prevent fractures induced by stress concentration, and the surfaces of the spacers were designed as either an isosceles triangle-shaped valley (V1) or a right triangle-shaped valley (V2). Linear analysis using finite element model (FEM) was performed, and Von Mises stress distribution was calculated by applying 1000 N of uniformly distributed load. Samples of the V2 design were made with bioactive glass-ceramics (BGS-7) and evaluated for compressive strength, fatigue degree, and impact strength. Von Mises stress was highest at the first tooth from the posterior side for the control group and at the center for the experimental group. Compared with the control group, the experimental group showed 18.4% and 82.5% reduction (V1 vs. T1 and V2 vs. T2, respectively) in the maximum stress at the bottom of the valleys. The FEM analysis revealed that the V2 design had the most even load distribution. The V2 samples with bioactive glass-ceramics were evaluated for compressive strength, and all six samples were not fractured up to 24 000 N. However, the average impact strength was 19.42 kN, suggesting that momentary force caused damage at a lower load than compression with a steady speed. The BGS-7 intervertebral disc spacer with V2 design was not fractured during the fatigue test at maximum pressure of 8000 N, R ≥10, 5 Hz, and 5 million cycles. These data confirm that the BGS-7 spacer with the V2 design may be clinically applicable. Collectively, the modified surface geometry of the experimental group significantly lowered Von Mises stress values at the bottom of the valleys, and thus the possibility of fracture by compressive load was greatly reduced. Also, impact during insertion was confirmed to cause fracture more easily, as the impact strength was lower than the compressive strength in the experimental group.
生物活性陶瓷椎间间隔物已被用于治疗退行性脊柱疾病。齿状间隔物通常用于防止迁移，但在插入或插入后存在骨折的可能性。等腰三角形齿（T1）或直角三角形齿（T2）的椎间间隔物用作对照组。实验组的设计因素进行了修改，以防止由应力集中引起的骨折，并且间隔物的表面设计为等腰三角形谷（V1）或直角三角形谷（V2）。使用有限元模型（FEM）进行线性分析，并通过施加 1000 N 的均匀分布载荷来计算 Von Mises 应力分布。用生物活性玻璃陶瓷（BGS-7）制造了 V2 设计的样品，并评估了抗压强度、疲劳程度和冲击强度。对于对照组，最大 Von Mises 应力在前侧的第一个齿处最高，对于实验组，最大 Von Mises 应力在中心处最高。与对照组相比，实验组谷底的最大应力分别降低了 18.4%和 82.5%（V1 与 T1 和 V2 与 T2）。有限元分析表明，V2 设计具有最均匀的载荷分布。对具有生物活性玻璃陶瓷的 V2 样品进行了抗压强度评估，所有六个样品在高达 24000 N 的压力下均未断裂。但是，平均冲击强度为 19.42 kN，这表明在较低的负载下，瞬间力会造成损坏，而不是以恒定速度进行压缩。在 8000 N 的最大压力、R≥10、5 Hz 和 500 万次循环的疲劳试验中，BGS-7 V2 设计椎间间隔物未发生断裂。这些数据证实，V2 设计的 BGS-7 间隔物可能具有临床应用价值。总的来说，实验组表面几何形状的修改显著降低了谷底的 Von Mises 应力值，从而大大降低了压缩载荷引起骨折的可能性。此外，在插入过程中确认冲击更容易导致骨折，因为实验组的冲击强度低于抗压强度。
