The three-dimensional rotational behaviors of the carpal bones.

The rotational behaviors of the carpal bones of ten fresh cadaver forearms were determined using a three-dimensional sonic digitizer, as the hands were passively moved through planar constrained motions. Changing forearm orientation from supination to pronation results in an increase in the magnitudes of extension of the proximal and distal carpal row bones and a reduction in the magnitudes of flexion of the distal carpal row bones. The included angles between each carpal bone screw displacement axis (SDA) and third metacarpal SDA for corresponding intervals of motion are significantly greater than zero, regardless of forearm orientation. The included angles of the proximal carpal row bones are significantly greater than those of the distal carpal row bones during third metacarpal radial-ulnar deviation. The carpal bone rotation magnitudes are significantly attenuated relative to the prescribed rotation magnitudes of the third metacarpal, with the exception of the trapezoid during third metacarpal extension. The rotational attenuation is greatest in the proximal carpal row bones and is most pronounced during third metacarpal flexion-extension motion and ulnar deviation. Evidence from this investigation favors a carpal row concept of wrist motion, as opposed to a carpal column model.