The facet joint contributes to lumbar spine stability as it supports the weight of body along with the intervertebral discs. However, most studies on the causes of degenerative lumbar diseases focus on the intervertebral discs and often overlook the facet joints. This study aimed to investigate the impact of facet joint degeneration on the degenerative changes and diseases of the lumbar spine. A finite element model of the lumbar spine (L1–S1) was fabricated and validated to study the biomechanical characteristics of the facet joints. To simulate degeneration of the facet joint, the model was divided into four grades based on the number of degenerative segments (L4–L5 or L4–S1) and the contact condition between the facet joint surfaces. Finite element analysis was performed on four spine motions: flexion, extension, lateral bending, and axial torsion, by applying a pure moment to the upper surface of L1. Important parameters that could be used to confirm the effect of facet joint degeneration on the lumbar spine were calculated, including the range of motion (ROM) of the lumbar segments, maximum von Mises stress on the intervertebral discs, and reaction force at the facet joint. Facet joint degeneration affected the biomechanical characteristics of the lumbar spine depending on the movements of the spine. When analyzed by dividing it into degenerative onset and onset-adjacent segments, lumbar ROM and the maximum von Mises stress of the intervertebral discs decreased as the degree of degeneration increased in the degenerative onset segments. The reaction force at the facet joint decreased with flexion and increased with lateral bending and axial torsion. In contrast, lumbar ROM of the onset-adjacent segments remained almost unchanged despite severe degeneration of the facet joint, and the maximum von Mises stress of the intervertebral discs increased with flexion and extension but decreased with lateral bending and axial torsion. Additionally, the facet joint reaction force increased with extension, lateral bending, and axial rotation. This analysis, which combined the ROM of the lumbar segment, maximum von Mises stress on the intervertebral disc, and facet joint reaction force, confirmed the biomechanical changes in the lumbar spine due to the degeneration of isolated facet joints under the load of spinal motion. In the degenerative onset segment, spinal instability decreased, whereas in the onset-adjacent segment, a greater load was applied than in the intact state. When conducting biomechanical studies on the lumbar spine, considering facet joint degeneration is important since it can lead to degenerative spinal diseases, including adjacent segment diseases.

中文翻译：

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分析腰椎小关节的孤立退变：使用有限元分析对退变不稳定性和腰椎生物力学的影响

小关节有助于腰椎的稳定性，因为它与椎间盘一起支撑身体的重量。然而，大多数关于退行性腰椎疾病病因的研究都集中在椎间盘上，而往往忽视了小关节。本研究旨在探讨小关节退变对腰椎退行性改变和疾病的影响。制作并验证了腰椎 (L1–S1) 的有限元模型，以研究小关节的生物力学特征。为了模拟小关节的退变，根据退变节段的数量（L4-L5或L4-S1）和小关节表面之间的接触情况将模型分为四个等级。通过对 L1 的上表面施加纯力矩，对四种脊柱运动进行有限元分析：屈曲、伸展、侧向弯曲和轴向扭转。计算了可用于确认小关节退变对腰椎影响的重要参数，包括腰椎节段的运动范围（ROM）、椎间盘上的最大冯米塞斯应力以及小关节的反作用力。小关节退变影响了腰椎的生物力学特征，这取决于脊柱的运动。将其分为退变起始段和起始相邻节段进行分析时，腰椎活动度和椎间盘最大von Mises应力随着退变起始段退变程度的增加而降低。小关节处的反作用力随着屈曲而减小，随着侧向弯曲和轴向扭转而增大。相比之下，尽管小关节严重退变，起始相邻节段的腰椎活动度几乎保持不变，椎间盘的最大 von Mises 应力随着屈曲和伸展而增加，但随着侧向弯曲和轴向扭转而减小。此外，小关节反作用力随着伸展、横向弯曲和轴向旋转而增加。该分析结合了腰椎节段的活动度、椎间盘上的最大 von Mises 应力和小关节反作用力，证实了由于脊柱运动负荷下孤立的小关节退变而引起的腰椎生物力学变化。在退变的起始节段中，脊柱不稳定性减少，而在起始相邻节段中，施加了比完整状态更大的负载。在对腰椎进行生物力学研究时，考虑小关节退变很重要，因为它可能导致退行性脊柱疾病，包括邻近节段疾病。