Zhu Rui, Niu Wen-Xin, Zeng Zhi-Li, Tong Jian-Hua, Zhen Zhi-Wei, Zhou Shuang, Yu Yan, Cheng Li-Ming
Spine Division of Orthopaedic Department, Tongji Hospital, Tongji University School of Medicine, 389 Xincun Road, 200065 Shanghai, China; Department of Histology and Embryology, Tongji University School of Medicine, 1239 Siping Road, Shanghai 200092, China.
Spine Division of Orthopaedic Department, Tongji Hospital, Tongji University School of Medicine, 389 Xincun Road, 200065 Shanghai, China.
Clin Biomech (Bristol). 2017 Jan;41:34-38. doi: 10.1016/j.clinbiomech.2016.11.007. Epub 2016 Nov 26.
Whether muscle weakness is a cause, or result, of degenerative spondylolisthesis is not currently well understood. Little biomechanical evidence is available to offer an explanation for the mechanism behind exercise therapy. Therefore, the aim of this study is to investigate the effects of back muscle weakness on degenerative spondylolisthesis and to tease out the biomechanical mechanism of exercise therapy.
A nonlinear 3-D finite element model of L3-L5 was constructed. Forces representing global back muscles and global abdominal muscles, follower loads and an upper body weight were applied. The force of the global back muscles was reduced to 75%, 50% and 25% to simulate different degrees of back muscle weakness. An additional boundary condition which represented the loads from other muscles after exercise therapy was set up to keep the spine in a neutral standing position. Shear forces, intradiscal pressure, facet joint forces and von Mises equivalent stresses in the annuli were calculated.
The intervertebral rotations of L3-L4 and L4-L5 were within the range of in vitro experimental data. The calculated intradiscal pressure of L4-L5 for standing was 0.57MPa, which is similar to previous in vivo data. With the back muscles were reduced to 75%, 50% and 25% force, the shear force moved increasingly in a ventral direction. Due to the additional stabilizing force and moment provided by boundary conditions, the shear force varied less than 15%.
Reducing the force of global back muscles might lead to, or aggravate, degenerative spondylolisthesis with forward slipping from biomechanical point of view. Exercise therapy may improve the spinal biomechanical environment. However, the intrinsic correlation between back muscle weakness and degenerative spondylolisthesis needs more clinical in vivo study and biomechanical analysis.
目前对于肌肉无力是退变性腰椎滑脱的原因还是结果尚未完全明确。几乎没有生物力学证据能够解释运动疗法背后的机制。因此，本研究的目的是探讨背部肌肉无力对退变性腰椎滑脱的影响，并梳理出运动疗法的生物力学机制。
构建了L3-L5的非线性三维有限元模型。施加代表整体背部肌肉和整体腹部肌肉的力、随动载荷和上身重量。将整体背部肌肉的力分别降低至75%、50%和25%，以模拟不同程度的背部肌肉无力。设置了一个额外的边界条件，该条件代表运动疗法后其他肌肉的载荷，以使脊柱保持中立站立姿势。计算了剪切力、椎间盘内压力、小关节力和椎间盘环中的冯·米塞斯等效应力。
L3-L4和L4-L5的椎间旋转在体外实验数据范围内。计算得出站立时L4-L5的椎间盘内压力为0.57MPa，与先前的体内数据相似。当背部肌肉力降低至75%、50%和25%时，剪切力越来越向腹侧移动。由于边界条件提供了额外的稳定力和力矩，剪切力变化小于15%。
从生物力学角度来看，降低整体背部肌肉的力可能导致或加重退变性腰椎滑脱并伴有向前滑移。运动疗法可能会改善脊柱生物力学环境。然而，背部肌肉无力与退变性腰椎滑脱之间的内在关联需要更多的临床体内研究和生物力学分析。
