Influence of the Diameter of Grasped Spheres on the Rotation Angle and Axis of the Second to Fifth Carpometacarpal Joints

Abstract

While previous studies have investigated the range of motion of the carpometacarpal (CMC) joints, there have been no results reported regarding the effects of the size of the grasped object. Therefore, we used a finite helical axis representation to investigate the rotation angles and rotation axes of the second to fifth CMC joints when three spheres with different diameters were grasped. Nine Japanese men were selected. Three-dimensional bone models were constructed based on cross-sectional images of the hand using X-ray computed tomography. Imaging was conducted under four conditions: a baseline posture without holding a sphere and postures in which three spheres with different diameters (table tennis ball: 40-mm; tennis ball: 67-mm; softball: 97-mm) were grasped. For all grasped spheres, the rotation angle was smallest for the third CMC joint and largest for the fifth CMC joint. Rotation angles were almost the same for all CMC joints regardless of the size of the grasped sphere. To quantitatively evaluate rotation axes, the angle created with the Z-axis (radioulnar axis) when the rotation axis was projected on the YZ plane (coronal plane) was defined as α (− 90° < α ≤ 90°). For the rotational axis, α angles of the second and fifth CMC joints tended to decrease as the diameter of the grasped sphere increased. Results demonstrated that in the spheres examined in the present study, CMC joint rotation axes rather than angles changed in response to differences in sphere size.