小关节角矢状化、椎间盘退变对退变性腰椎滑移作用的有限元研究

Contribution of sagittal orientation of facet joints and disc degeneration to degenerative spondylolisthesis in lumbar spine:A finite element research

目的探讨小关节矢状化与椎间盘退变间的关系及其对退变性腰椎滑移的作用和意义。方法采用一种新型CAD方法精确构建65°小关节角、45°小关节角、25°小关节角与正常椎间盘、轻度退变椎间盘、重度退变椎间盘相组配的9种腰椎L4-L5活动节段有限元模型。生理压缩载荷下,分别对9种有限元模型的生物力学参数进行测试。结果与小关节角45°和25°有限元模型相比,小关节角65°有限元模型的矢状方向椎体前移位增加,关节突、峡部等效应力和关节突水平方向接触力明显增加;小关节角65°有限元模型的终板膨出减小,纤维环基质应力增加。与正常有限元模型相比,椎间盘轻度退变有限元模型刚度下降,小关节突及峡部应力轻度增加。9种有限元模型中,轻度退变椎间盘结合小关节角65°有限元模型的抗前剪力能力最差。结论小关节角矢状化既是退变性腰椎滑移的原发诱因,又是局部应力变化导致关节突再塑形的继发病理改变,矢状型小关节腰椎活动节段矢状方向内在不稳定性受椎间盘退变程度的影响,椎间盘退变对小关节角矢状化无明显促进作用。

Objective To research the connection between the sagittal orientation of facet joints and disc degeneration in lumbar spine and to investigate the contribution of which to development the degenerative spondylolisthesis. Methods A new effective CAD method was used to accurately establish 9 finite element models（FEM）which were assembled respectively with facet-joint angle 65°, 45°, 25°, with normal disc, light degenerative disc and severe degenerative disc. The biomechanical parameters of 9 finite element models were measured under axial compressive load within physiological range. Results Compared with FEMs with facet-joint angle 45° and 25°, anterior displacement of L4 vertebra in FEMs with facet-joint angle 65° was increased, where the maximum yon Mises stresses on facet surface, isthmus and the contact force on facet surface in horizontal orientation were obviously increased. Meanwhile, FEMs with facet-joint angle 65° showed a decrease in end-plate bulge and an increase in stress of annular matrix. The stiffness in light degenerative disc FEMs was reduced and the yon Mises stresses on facet surface and isthmus was slightly increased compared with the normal disc FEMs. Among all, the FEM with facet-joint angle 65° combined with light degenerative disc showed the poorest resisting anterior shear force. Conclusion Sagittal orientation of facet joints is not only the primary inducement of the degenera- tive spondylolisthesis but the secondary pathological change of remodeling of the facet-joints induced by the regional stress change. The inherent instability of lumbar motion segment of sagittal orientation of facet joints is influenced by the lumbar disc degeneration. The lumbar disc degeneration has no manifested contribution to the aggravation of the sagittal orientation of facet joints.