The instantaneous helical axis (IHA) is a characteristic of neck movement that is very sensitive to changes in coordination and that has potential in the assessment of functional alterations. For its application in the clinical setting, normative patterns must be available, and its reliability must be established. The purpose of this work is to describe the continuous paths of the IHA during cyclic movements of flexion-extension (FE), lateral bending (LB), and axial rotation (AR) and to quantify their reliability. Fifteen healthy volunteers participated in the study; two repetitions were made on the same day (by different operators) and over an 8-day interval (by the same operator) to evaluate the inter-operator and inter-session reliability, respectively. The paths described by the IHA suggest a sequential movement of the vertebrae in the FE movement, with a large vertical displacement (mean, 10 cm). The IHA displacement in LB and AR movements are smaller. The paths described by the IHAs have a very high reliability for FE movement, although it is somewhat lower for LB and RA movements. The standard error of measurement (SEM) is less than 0.5 cm. These results show that the paths of the IHA are reliable enough to evaluate changes in the coordination of intervertebral movement. Graphical abstract A video photogrammetry system is used to record the cyclic movements of the neck, from which the continuous trajectories of the associated instantaneous helical axis (IHA) are calculated. We have analyzed the movements of flexion-extension (FE), lateral flexion (LB), and axial rotation (AR) for a sample of 15 healthy subjects. The measurements have been repeated with two different operators (in the same session) and in two separate sessions (same operator). IHA displacement patterns have been obtained in each movement, and the reliability of the measurement of such IHA trajectories has been estimated.

中文翻译：

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主动运动期间颈椎瞬时旋转轴的路径-模式和可靠性。

瞬时螺旋轴（IHA）是颈部运动的特征，对协调的变化非常敏感，并且在评估功能改变方面具有潜力。对于其在临床环境中的应用，必须有规范的模式，并且必须建立其可靠性。这项工作的目的是描述IHA在屈伸（FE），横向弯曲（LB）和轴向旋转（AR）循环运动期间的连续路径，并对其可靠性进行量化。15名健康志愿者参加了研究。在同一天（由不同的操作员）和在8天的间隔（由同一操作员）中进行两次重复，分别评估操作员之间和会话间的可靠性。IHA所描述的路径表明，椎骨在FE运动中是连续运动的，垂直位移较大（平均10厘米）。LB和AR运动中的IHA位移较小。IHA所描述的路径对于FE运动具有很高的可靠性，尽管对于LB和RA运动则略低。测量的标准误差（SEM）小于0.5厘米。这些结果表明，IHA的路径足够可靠，可以评估椎间运动协调性的变化。图形摘要视频摄影测量系统用于记录颈部的周期性运动，从中可以计算出相关的瞬时螺旋轴（IHA）的连续轨迹。我们分析了屈伸（FE），侧屈（LB），和15个健康受试者的样本的轴向旋转（AR）。已使用两个不同的操作员（在同一会话中）和两个单独的会话（同一操作员）重复进行了测量。已在每个运动中获得了IHA位移模式，并且已估算了此类IHA轨迹的测量可靠性。