Raza Ali, Howell Gwynneth T, Michalek Arthur J
Department of Mechanical & Aerospace Engineering Clarkson University Potsdam New York USA.
JOR Spine. 2024 Jul 25;7(3):e1361. doi: 10.1002/jsp2.1361. eCollection 2024 Sep.
The annulus fibrosus (AF) of the Intervertebral disc (IVD) is composed of concentric lamellae of helically wound collagen fibers. Understanding the spatial variation of collagen fiber orientations in these lamellae, and the resulting material anisotropy, is crucial to predicting the mechanical behavior of the complete IVD.
This study builds on a prior model predicated on path-independent displacement of fiber endpoints during vertebral body growth to predict a complete, three-dimensional annulus fibrosus fiber network from a small number of subject-independent input parameters and vertebral endplate topographies obtained from clinical imaging. To evaluate the model, it was first fit to mid-plane fiber orientations obtained using polarized light microscopy in a population of bovine caudal discs for which computed tomography images vertebral endplates were also available. Additionally, the model was used to predict the trajectories based on human lumbar disc geometries and results were compared to previously reported data. Finally, the model was employed to investigate potential disc-related variations in fiber angle distributions.
The model was able to accurately predict experimentally measured fiber distributions in both bovine and human discs using only endplate topography and three input parameters. Critically, the model recapitulated previously observed asymmetry between the inclinations of right- and left-handed fibers in the posterolateral aspect of the human AF. Level to level variation of disc height and aspect ratio in the human lumbar spine was predicted to affect absolute values of fiber inclination, but not this asymmetry.
Taken together these results suggest that patient-specific distributions of AF fiber orientation may be readily incorporated into computational models of the spine using only disc geometry and a small number of subject-independent parameters.
椎间盘（IVD）的纤维环（AF）由螺旋状缠绕的胶原纤维同心薄片组成。了解这些薄片中胶原纤维取向的空间变化以及由此产生的材料各向异性，对于预测完整椎间盘的力学行为至关重要。
本研究基于先前的一个模型，该模型基于椎体生长过程中纤维端点的与路径无关的位移，从少量与个体无关的输入参数和从临床成像获得的椎体终板地形来预测完整的三维纤维环纤维网络。为了评估该模型，首先将其拟合到使用偏振光显微镜在一组牛尾椎间盘获得的中平面纤维取向上，对于这些椎间盘也可获得计算机断层扫描图像的椎体终板。此外，该模型用于根据人类腰椎间盘几何形状预测轨迹，并将结果与先前报道的数据进行比较。最后，该模型用于研究纤维角度分布中潜在的与椎间盘相关的变化。
该模型仅使用终板地形和三个输入参数就能准确预测牛和人椎间盘实验测量的纤维分布。至关重要的是，该模型重现了先前在人类纤维环后外侧观察到的右手和左手纤维倾斜度之间的不对称性。预计人类腰椎间盘高度和纵横比的节段间变化会影响纤维倾斜度的绝对值，但不会影响这种不对称性。
综合这些结果表明，仅使用椎间盘几何形状和少量与个体无关的参数，就可以很容易地将特定患者的纤维环纤维取向分布纳入脊柱的计算模型中。
