Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
Department of Rehabilitation Medicine, University of Minnesota, Minneapolis, MN 55455, USA.
J R Soc Interface. 2018 Nov 14;15(148):20180550. doi: 10.1098/rsif.2018.0550.
Due to its high level of innervation, the lumbar facet capsular ligament (FCL) is suspected to play a role in low back pain (LBP). The nociceptors in the lumbar FCL may experience excessive deformation and generate pain signals. As such, understanding the mechanical behaviour of the FCL, as well as that of its underlying nerves, is critical if one hopes to understand its role in LBP. In this work, we constructed a multiscale structure-based finite-element (FE) model of a lumbar FCL on a spinal motion segment undergoing physiological motions of flexion, extension, ipsilateral and contralateral bending, and ipsilateral axial rotation. Our FE model was created for a generic FCL geometry by morphing a previously imaged FCL anatomy onto an existing generic motion segment model. The fibre organization of the FCL in our models was subject-specific based on previous analysis of six dissected specimens. The fibre structures from those specimens were mapped onto the FCL geometry on the motion segment. A motion segment model was used to determine vertebral kinematics under specified spinal loading conditions, providing boundary conditions for the FCL-only multiscale FE model. The solution of the FE model then provided detailed stress and strain fields within the tissue. Lastly, we used this computed strain field and our previous studies of deformation of nerves embedded in fibrous networks during simple deformations (e.g. uniaxial stretch, shear) to estimate the nerve deformation based on the local tissue strain and fibre alignment. Our results show that extension and ipsilateral bending result in largest strains of the lumbar FCL, while contralateral bending and flexion experience lowest strain values. Similar to strain trends, we calculated that the stretch of the microtubules of the nerves, as well as the forces exerted on the nerves' membrane are maximal for extension and ipsilateral bending, but the location within the FCL of peak microtubule stretch differed from that of peak membrane force.
由于其高度的神经支配，腰椎小关节囊韧带（FCL）被怀疑在腰痛（LBP）中起作用。腰椎 FCL 中的伤害感受器可能会经历过度变形并产生疼痛信号。因此，如果希望了解 FCL 在 LBP 中的作用，了解 FCL 及其下神经的机械行为至关重要。在这项工作中，我们构建了一个在经历生理弯曲、伸展、同侧和对侧弯曲以及同侧轴向旋转运动的脊柱运动节段上的腰椎 FCL 的基于多尺度结构的有限元（FE）模型。我们的 FE 模型是通过将先前成像的 FCL 解剖结构变形到现有的通用运动节段模型上来为通用 FCL 几何形状创建的。我们模型中的 FCL 纤维组织是基于对六个解剖标本的先前分析的基于个体的。从这些标本中提取的纤维结构被映射到运动节段上的 FCL 几何形状上。使用运动节段模型确定特定脊柱加载条件下的椎体运动学，为仅 FCL 的多尺度 FE 模型提供边界条件。FE 模型的解然后提供组织内详细的应力和应变场。最后，我们使用该计算应变场和我们之前对嵌入在纤维网络中的神经在简单变形（例如单轴拉伸、剪切）过程中的变形的研究，根据局部组织应变和纤维排列来估计神经变形。我们的结果表明，伸展和同侧弯曲导致腰椎 FCL 的应变最大，而对侧弯曲和弯曲的应变值最低。与应变趋势类似，我们计算出神经的微管的拉伸以及神经膜上的力在伸展和同侧弯曲时最大，但微管拉伸的峰值位置与膜力的峰值位置不同。
