The motion analysis of two-finger tip pinching using the thumb and index finger provides crucial data for designing the motion mechanism of electric prosthetic hands. The purpose of this study is to determine the joints that have high mobility during two-finger tip pinching by measuring the flexion angle of each joint. Ten Japanese men with normal hand were selected. CT images were obtained while the hands adopted the following four postures: a basic posture not pinching a cylinder, and three postures pinching wooden cylinders with different diameters (2, 10, and 30 mm). Three-dimensional bone models of the thumb and index finger were created using the CT images and used to measure the flexion angles of the joints. The flexion angles of the proximal interphalangeal and metacarpophalangeal joints of the index finger significantly decreased as the diameter of the cylinder increased. However, even when the diameter of the cylinder changed, the flexion angle of the distal interphalangeal joint of the index finger, and the flexion and rotation angles of all of the thumb joints did not change. When pinching objects of different sizes with a two-finger tip pinch, the posture of the thumb is fixed, and only the posture of the index finger changes. When designing the two-finger tip pinch motion for an electric prosthetic hand, it is sufficient to drive the joints of the index finger only.

中文翻译：

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使用从X射线计算机断层扫描（CT）图像构建的3D骨模型，在两指尖捏合中手指关节的弯曲角度。

使用拇指和食指捏住两个手指的运动分析为设计电动假手的运动机理提供了关键数据。这项研究的目的是通过测量每个关节的屈曲角度来确定在两指尖头捏合过程中具有高活动性的关节。选择十名日本人的正常手。双手采取以下四个姿势时获得了CT图像：基本姿势不挤压圆柱体，三个姿势挤压木质圆柱体（直径分别为2、10和30 mm）。使用CT图像创建了拇指和食指的三维骨骼模型，并用于测量关节的弯曲角度。食指的近端指间关节和掌指关节的屈曲角度随着圆柱体直径的增加而显着降低。然而，即使当圆柱体的直径改变时，食指的远侧指间关节的弯曲角度以及所有拇指关节的弯曲和旋转角度也没有改变。用两根手指捏住不同大小的物体时，拇指的姿势是固定的，只有食指的姿势会发生变化。在设计假肢手的两指尖捏动作时，仅驱动食指的关节就足够了。并且所有拇指关节的弯曲角度和旋转角度均未改变。用两根手指捏捏不同大小的物体时，拇指的姿势是固定的，只有食指的姿势会发生变化。在设计假肢手的两指尖捏动作时，仅驱动食指的关节就足够了。并且所有拇指关节的弯曲角度和旋转角度均未改变。用两根手指捏捏不同大小的物体时，拇指的姿势是固定的，只有食指的姿势会发生变化。在设计假肢手的两指尖捏动作时，仅驱动食指的关节就足够了。