Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN.
Department of Neurologic Surgery, Mayo Clinic, Rochester, MN.
Spine (Phila Pa 1976). 2023 Jan 15;48(2):127-136. doi: 10.1097/BRS.0000000000004470. Epub 2022 Sep 6.
In vitro study.
The purpose of the present study was to utilize an idealized cervical spine model to determine whether the parallax effect or changes in the position of the spine relative to the x-ray generator influence intervertebral motion parameters on dynamic cervical spine radiographs.
The utility of flexion-extension radiographs in clinical practice remains in question due to poor reliability of the parameters utilized to measure motion.
A cervical spine model with tantalum beads inserted into the tip of each spinous process was utilized to measure interspinous process distance (IPD) on plain radiographs. The model was then manipulated to alter the generator angle and generator distance, and the IPD was measured. The impact of individual and combined changes in these parameters on IPD was assessed. Multivariate analysis was performed to identify independent drivers of variability in IPD measurements.
Isolated changes in the generator distance and generator angle and combined changes in these parameters led to significant changes in the measured IPD at each intervertebral level in neutral, flexion, and extension, which, in many instances, exceeded an absolute change of >1 mm or >2 mm. Multivariate analysis revealed that generator distance and generator angle are both independent factors impacting IPD measurements that have an additive effect.
In an idealized cervical spine model, small clinically feasible changes in spine position relative to the x-ray generator produced substantial variability in IPD measurements, with absolute changes that often exceeded established cutoffs for determining the presence of pathologic motion across a fused segment. This study further reinforces that motion assessment on dynamic radiographs is not a reliable method for determining the presence of an arthrodesis unless these sources of variability can be consistently eliminated.
体外研究。
本研究旨在利用理想化的颈椎模型，确定视差效应或脊柱相对于 X 射线发生器位置的变化是否会影响颈椎动态 X 光片上的椎间运动参数。
由于用于测量运动的参数的可靠性较差，屈伸位 X 光片在临床实践中的实用性仍存在疑问。
使用在每个棘突尖端插入钽珠的颈椎模型来测量 X 光片上的棘突间距离（IPD）。然后，对模型进行操作以改变发生器角度和发生器距离，并测量 IPD。评估这些参数的个体和组合变化对 IPD 的影响。进行多变量分析以确定 IPD 测量值变化的独立驱动因素。
单独改变发生器距离和发生器角度以及这些参数的组合变化导致在中立、屈伸位时每个椎间水平的测量 IPD 发生显著变化，在许多情况下，变化超过了 >1 毫米或 >2 毫米的绝对变化。多变量分析显示，发生器距离和发生器角度都是影响 IPD 测量的独立因素，具有累加效应。
在理想化的颈椎模型中，脊柱相对于 X 射线发生器的位置发生微小的临床可行变化，会导致 IPD 测量值出现显著变化，绝对值变化通常超过确定融合节段病理性运动存在的既定临界点。本研究进一步证实，除非能够始终消除这些变化源，否则动态 X 光片上的运动评估不是确定融合术存在的可靠方法。
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