Division of Research, Logan University, 1851 Schoettler Rd., Chesterfield, MO 63017, USA.
Spine J. 2010 Dec;10(12):1069-77. doi: 10.1016/j.spinee.2010.09.012.
Nerve fiber growth inside the degenerative intervertebral discs and facets is thought to be a source of pain, although there may be several other pathological and clinical reasons for the neck pain. It, however, remains difficult to decipher how much disc and facet joints contribute to overall degenerative segmental responses. Although the biomechanical effects of disc degeneration (DD) on segmental flexibility and posterior facets have been reported in the lumbar spine, a clear understanding of the pathways of degenerative progression is still lacking in the cervical spine.
To test the hypothesis that after an occurrence of degenerative disease in a cervical disc, changes in the facet loads will be higher than changes in the disc pressure.
To understand the biomechanical relationships between segmental flexibility, disc pressure, and facet loads when the C5-C6 disc degenerates.
A poroelastic, three-dimensional finite element (FE) model of a normal C5-C6 segment was developed and validated. Two degenerated disc models (moderate and severe) were built from the normal disc model. Biomechanical responses of the three FE models (normal, moderate, and severe) were further studied under diurnal compression (at the end of the daytime activity period) and moment loads (at the end of 5 seconds) in terms of disc height loss, angular motions, disc pressure, and facet loads (average of right and left facets).
Disc deformation under compression and segmental rotational motions under moment loads for the normal disc model agreed well with the corresponding in vivo studies. A decrease in segmental flexibility because of DD is accompanied by a decrease in disc pressure and an increase in facet loads. Biomechanical effects of degenerative disc changes are least in flexion. Segmental flexibility changes are higher in extension, whereas changes in disc pressure and facet loads are higher in lateral bending and axial rotation, respectively.
The results of the present study confirmed the hypothesis of higher changes in facet loads than in disc pressure, suggesting posterior facets are more affected than discs because of a decrease in degenerative segmental flexibility. Therefore, a degenerated disc may increase the risk of overloading the posterior facet joints. It should be clearly noted that only after degeneration simulation in the disc, we recorded the biomechanical responses of the facets and disc. Therefore, our hypothesis does not suggest that facet joint osteoarthritis may occur before degeneration in the disc. Future cervical spine-based experiments are warranted to verify the conclusions presented in this study.
在退行性椎间盘和小关节内的神经纤维生长被认为是疼痛的一个来源，尽管颈部疼痛可能还有其他几个病理和临床原因。然而，要确定椎间盘和小关节对整体退行性节段反应的贡献程度仍然很困难。虽然腰椎间盘退行性变（DD）对节段柔韧性和后路小关节的生物力学影响已有报道，但颈椎退行性进展的途径仍不清楚。
检验以下假设，即颈椎间盘发生退行性疾病后，小关节负荷的变化将高于椎间盘压力的变化。
为了了解 C5-C6 椎间盘退变时节段柔韧性、椎间盘压力和小关节负荷之间的生物力学关系。
建立并验证了一个正常 C5-C6 节段的多孔弹性三维有限元（FE）模型。从正常椎间盘模型中构建了两个退行性椎间盘模型（中度和重度）。进一步研究了三种 FE 模型（正常、中度和重度）在日间压缩（白天活动结束时）和力矩载荷（5 秒结束时）下的生物力学响应，包括椎间盘高度损失、角运动、椎间盘压力和小关节负荷（右侧和左侧小关节的平均值）。
正常椎间盘模型在压缩下的椎间盘变形和在力矩载荷下的节段旋转运动与相应的体内研究吻合良好。由于 DD 导致节段柔韧性降低，同时伴随着椎间盘压力降低和小关节负荷增加。退行性椎间盘变化的生物力学效应在屈曲时最小。节段柔韧性的变化在伸展时更高，而椎间盘压力和小关节负荷的变化分别在侧屈和轴向旋转时更高。
本研究结果证实了这样的假设，即小关节负荷的变化比椎间盘压力的变化更大，这表明由于退行性节段柔韧性降低，后路小关节比椎间盘更容易受到影响。因此，退行性椎间盘可能会增加后路小关节过度负荷的风险。需要明确的是，只有在椎间盘发生退行性变的模拟之后，我们才记录了小关节和椎间盘的生物力学反应。因此，我们的假设并不表明小关节骨关节炎可能在椎间盘退行性变之前发生。未来需要基于颈椎的实验来验证本研究提出的结论。
