Development of Kinematic Graphs of Median Nerve during Active Finger Motion: Implications of Smartphone Use

BackgroundCertain hand activities cause deformation and displacement of the median nerve at the carpal tunnel due to the gliding motion of tendons surrounding it. As smartphone usage escalates, this raises the public’s concern whether hand activities while using smartphones can lead to median nerve problems.ObjectiveThe aims of this study were to 1) develop kinematic graphs and 2) investigate the associated deformation and rotational information of median nerve in the carpal tunnel during hand activities.MethodsDominant wrists of 30 young adults were examined with ultrasonography by placing a transducer transversely on their wrist crease. Ultrasound video clips were recorded when the subject performing 1) thumb opposition with the wrist in neutral position, 2) thumb opposition with the wrist in ulnar deviation and 3) pinch grip with the wrist in neutral position. Six still images that were separated by 0.2-second intervals were then captured from the ultrasound video for the determination of 1) cross-sectional area (CSA), 2) flattening ratio (FR), 3) rotational displacement (RD) and 4) translational displacement (TD) of median nerve in the carpal tunnel, and these collected information of deformation, rotational and displacement of median nerve were compared between 1) two successive time points during a single hand activity and 2) different hand motions at the same time point. Finally, kinematic graphs were constructed to demonstrate the mobility of median nerve during different hand activities.ResultsPerforming different hand activities during this study led to a gradual reduction in CSA of the median nerve, with thumb opposition together with the wrist in ulnar deviation causing the greatest extent of deformation of the median nerve. Thumb opposition with the wrist in ulnar deviation also led to the largest extent of TD when compared to the other two hand activities of this study. Kinematic graphs showed that the motion pathways of median nerve during different hand activities were complex.ConclusionWe observed that the median nerve in the carpal tunnel was rotated, deformed and displaced during the hand activities that people may be performed when using a smartphone, suggesting an increased risk of carpal tunnel syndrome (CTS). In addition, the kinematic graphs of median nerve developed in the present study provide new clues for further studies on the pathophysiology of CTS, and alerting smartphone users to establish proper postural habits when using handheld electronic devices.

背景 部分手部活动可因周围肌腱的滑动运动，导致腕管内正中神经发生形变与移位。随着智能手机使用量攀升，公众愈发担忧使用智能手机时的手部活动是否会引发正中神经相关病症。
目的 本研究旨在：1）构建运动学图谱；2）探究手部活动过程中腕管内正中神经的相关形变与旋转信息。
方法 本研究对30名年轻成年人的优势侧腕部进行超声检查：将超声探头横向置于腕横纹处。受试者完成以下3种动作时录制超声视频片段：1）腕部处于中立位时的拇指对掌动作；2）腕部处于尺偏位时的拇指对掌动作；3）腕部处于中立位时的捏握动作。随后从超声视频中截取间隔0.2秒的6帧静态图像，以测定腕管内正中神经的1）横截面积（cross-sectional area, CSA）、2）扁平率（flattening ratio, FR）、3）旋转移位（rotational displacement, RD）及4）平移移位（translational displacement, TD）。随后对比两类数据：①单次手部活动中两个连续时间点的正中神经形变、旋转及移位信息；②同一时间点下不同手部活动对应的上述信息。最终构建运动学图谱，以展示不同手部活动过程中正中神经的活动度。
结果 本研究中，完成不同手部活动可导致正中神经横截面积逐渐减小，其中腕部尺偏位的拇指对掌动作引发的正中神经形变程度最大。与本研究中的另外两种手部活动相比，腕部尺偏位的拇指对掌动作还会导致最大程度的平移移位。运动学图谱显示，不同手部活动过程中正中神经的运动通路较为复杂。
结论 本研究观察到，人们使用智能手机时可能进行的手部活动会导致腕管内正中神经发生旋转、形变与移位，这提示腕管综合征（carpal tunnel syndrome, CTS）的发病风险升高。此外，本研究构建的正中神经运动学图谱为腕管综合征病理生理学的后续研究提供了新的思路，同时也提醒智能手机使用者在使用手持电子设备时应养成正确的姿势习惯。