Background

The motion path of instantaneous center of rotation (ICR) is a crucial kinematic parameter to dynamically characterize cervical spine intervertebral patterns of motion; however, few studies have evaluated the effect of cervical disc degeneration (CDD) on ICR motion path. The purpose of this study was to investigate the effect of CDD on the ICR motion path of degenerated and adjacent segments.

Method

A validated nonlinear three-dimensional finite element (FE) model of a healthy adult cervical spine was used. Progressive degeneration was simulated with six FE models by modifying intervertebral disc height and material properties, anterior osteophyte size, and degree of endplate sclerosis at the C5–C6 level. All models were subjected to a pure moment of 1 Nm and a compressive follower load of 73.6 N to simulate physical motion. ICR motion paths were compared among different models.

Results

The normal FE model results were consistent with those of previous studies. In degenerative models, average ICR motion paths shifted significantly anterior at the degenerated segment (β = 0.27 mm; 95% CI: 0.22, 0.32) and posterior at the proximal adjacent segment (β = −0.09 mm; 95% CI: −0.15, −0.02) than those of the normal model.

Conclusion

CDD significantly affected ICR motion paths at the degenerated and proximal adjacent segments. The changes at adjacent segments may be a result of compensatory mechanisms to maintain the balance of the cervical spine. Surgical treatment planning should take into account the restoration of ICR motion path to normal. These findings could provide a basis for prosthesis design and clinical practice.

中文翻译：

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颈椎间盘退变对退行及邻近节段瞬时旋转中心运动路径的影响：有限元分析

背景

瞬时旋转中心（ICR）的运动路径是一个关键的运动学参数，可以动态表征颈椎椎间运动模式。但是，很少有研究评估颈椎间盘退变（CDD）对ICR运动路径的影响。这项研究的目的是调查CDD对变性和邻近节段的ICR运动路径的影响。

方法

使用经过验证的健康成人颈椎的非线性三维有限元（FE）模型。通过修改椎间盘高度和材料特性，前骨赘大小以及终板硬化程度（在C5至C6水平），使用六个有限元模型对进行性退化进行了模拟。所有模型均承受1 Nm的纯力矩和73.6 N的压缩从动载荷，以模拟物理运动。在不同模型之间比较了ICR运动路径。

结果

正常的有限元模型结果与先前的研究一致。在退化模型中，平均ICR运动路径在退化段明显向前移动（β  = 0.27 mm； 95％CI：0.22，0.32），而在近端相邻段向后移动（β  = -0.09 mm； 95％CI：-0.15， -0.02）。

结论

CDD严重影响了变性和近端相邻节段的ICR运动路径。相邻节段的变化可能是维持颈椎平衡的补偿机制的结果。手术治疗计划应考虑ICR运动路径恢复正常。这些发现可以为假体设计和临床实践提供基础。