Goel V K, Monroe B T, Gilbertson L G, Brinckmann P
Iowa Spine Research Center, Department of Biomedical Engineering and Orthopaedics, University of Iowa, USA.
Spine (Phila Pa 1976). 1995 Mar 15;20(6):689-98.
This study analyzed interlaminar shear stresses across the laminae of a ligamentous L3-L4 motion segment. A three-dimensional finite element model of the motion segment was developed and its response in axial compression mode was predicted.
The contributions of "mechanical" factors in producing laminae separation in a disc are not well understood, especially when the nucleus is still gel-like in appearance (stage 1 of disc degeneration). All types of stresses are likely to contribute to laminae separation. The authors believe it is partially due to the interlaminar shear stresses at the laminae interfaces in specific regions of an intact disc because the disc is a composite structure. The effects of anular tears on the interlaminar shear stresses were also investigated. These tears can be circumferential or radial in nature, and commonly occur in the aged, degenerated disc.
A large number of biomechanical studies dealing with the role of the disc vis-a-vis other spinal components have been reported in the literature. The role of mechanical factors, however, in producing laminae separation, especially when the nucleus is still gel-like in appearance (stage 1 of disc degeneration), is not entirely clear.
A three-dimensional nonlinear finite element model of an intact L3-L4 lumbar motion segment, based on the use of a special type of element for the disc anulus, was created to investigate the interlaminar shear stresses in the anulus. The effects of radial "out-in," radial "in-out," and "circumferential" injuries were analyzed. Injury was modeled as element removal in the posterolateral portion of the disc. Models subjected to axial compressive loads, ranging from 200 N to 2000 N, were analyzed. In addition to the interlaminar shear stresses, disc bulge, and displacements including coupled motions were predicted.
The theoretical disc bulge predictions for the radial in-out injury case were in agreement with the disc bulge data obtained experimentally. Displacements, disc bulge, and coupled motions increased with injury, as expected. The interlaminar shear stresses were highest in the posterolateral portions of the intact disc model. Interlaminar shear stresses, in general, increased with injury. Also, a slight increase in circumferential injury was sufficient to see a substantial increase in interlaminar shear stresses.
The interlaminar shear stresses being higher in the posterolateral regions of the intact disc reinforces that, from clinical studies, tears originate in the posterolateral portion of the disc. The large interlaminar shear stresses, caused by asymmetry in the disc structure due to injury, along with chemical and structural changes in the disc with age, may be an important cause of further degeneration through laminae separation. This is the case for traditional composite laminates. This study points out the importance of interlaminar shear stresses to gain further understanding of the role of mechanical factors in producing disc degeneration, especially delamination of the anulus. Clinical relevance of the findings and possible relationship to the aging process are explored.
本研究分析了L3 - L4韧带运动节段各层间的层间剪切应力。建立了该运动节段的三维有限元模型，并预测了其在轴向压缩模式下的响应。
椎间盘各层分离中“机械”因素的作用尚未完全明确，尤其是当髓核外观仍呈凝胶状时（椎间盘退变的第1阶段）。所有类型的应力都可能导致各层分离。作者认为部分原因在于完整椎间盘特定区域层间界面处的层间剪切应力，因为椎间盘是一种复合结构。还研究了环状撕裂对层间剪切应力的影响。这些撕裂在性质上可以是周向或径向的，且常见于老化、退变的椎间盘中。
文献中已报道了大量关于椎间盘相对于其他脊柱部件作用的生物力学研究。然而，机械因素在导致各层分离中的作用，尤其是当髓核外观仍呈凝胶状时（椎间盘退变的第1阶段），尚不完全清楚。
基于使用一种特殊类型的椎间盘纤维环单元，创建了一个完整L3 - L4腰椎运动节段的三维非线性有限元模型，以研究纤维环中的层间剪切应力。分析了径向“外 - 内”、径向“内 - 外”和“周向”损伤的影响。损伤通过去除椎间盘后外侧部分的单元来模拟。分析了承受200 N至2000 N轴向压缩载荷的模型。除了层间剪切应力外，还预测了椎间盘膨出以及包括耦合运动在内的位移。
径向“内 - 外”损伤情况下椎间盘膨出的理论预测值与实验获得的椎间盘膨出数据一致。如预期的那样，位移、椎间盘膨出和耦合运动随损伤程度增加。完整椎间盘模型后外侧部分的层间剪切应力最高。一般来说，层间剪切应力随损伤程度增加。此外，周向损伤的轻微增加足以使层间剪切应力大幅增加。
完整椎间盘后外侧区域的层间剪切应力较高，这进一步证明了临床研究中撕裂起源于椎间盘后外侧部分的观点。损伤导致椎间盘结构不对称所引起的较大层间剪切应力，以及随着年龄增长椎间盘的化学和结构变化，可能是通过各层分离导致进一步退变的重要原因。传统复合层压板的情况也是如此。本研究指出了层间剪切应力对于进一步理解机械因素在椎间盘退变尤其是纤维环分层中的作用的重要性。探讨了研究结果的临床相关性以及与衰老过程的可能关系。
