ROTATIONAL AXIS MOVEMENT OF THE WRIST DURING ULNA TO RADIAL DEVIATION.

Aim: The aim of this investigation was to determine how the rotational axis of the wrist moves as the hand goes from full ulna to full radial deviation. Materials & Methods: Ulna to radial deviation was assessed in 30 normal wrists in 15 normal subjects aged 19 to 32. Movement was measured with a Polhemus Fastrak (TM) magnetic tracking system. The system has translational and rotational measurement accuracies of 1 mm and 1 degree respectively. Subjects placed their palms on a flat wooded stool and had movement sensors attached over their 3rd metacarpal and distal radius. These sensors then recorded movement as the hand moved from full ulna to full radial deviation. Results: The mean range of movement was 47 degrees (SD 8). In full ulna deviation the wrist rotational axis was in the region of the lunate/capitate. As the hand moved towards radial deviation, the axis moved distally. At the end of the movement the mean distal displacement was 22 mm (SD 14). In 17 wrists the distal displacement was accompanied by mean displacement towards the ulna of 13 mm (SD 8). In 13 wrists the distal displacement was accompanied by a mean displacement towards the radius of 7 mm (SD 5). Conclusion: The rotational axis position indicates how the wrist is moving during radial deviation. In early movement, when the axis is proximal, there is a high degree of sideways translation. In later movement, when the axis is distal, there is more rotational movement. In some cases the axis moved distally and toward the radius, whereas in other cases it moved distally and toward the ulna. This spectrum of movement may support the theory of 2 type of carpal movement. i.e. Column movers and row movers [Craigen & Stanley].