Motion Analysis of the Carpometacarpal Joint of the Thumb Using Three-dimensional Computed Tomography

Abstract

To clarify the motion of the first metacarpal bone (1^st MC) of the trapezium (Tz), the author took 3D-CT images of his own thumb in six positions : neutral, flexion, extension, adduction, abduction and opposition. Based on these images, these six positions were reconstructed using bone models of the 1^st MC and the Tz. In the neutral position, the axis of the 1^st MC was on the perpendicular axis of the Tz. The axis of the 1^st MC was flexed at 16°, adducted 10° and pronated 5° in flexion, extended 9°, abducted 5° and pronated 9° in extension, flexed 9°, adducted 40° and supinated 16° in adduction, flexed 0°, abducted 10° and pronated 11° in abduction, and flexed 15°, abducted 10° and pronated 30° in opposition. The main contacts of the Tz and 1^st MC were both central to volar in flexion, both radial in extension, radial and ulnar in adduction, both radial in abduction, and volar and radiovolar in opposition. Three-dimensional analysis of the position of the 1^st MC on the Tz in these six positions allowed the main contact areas of the Tz and 1^st MC to be deduced.