VARIATION IN THE ROTATIONAL AXIS MOVEMENT OF THE WRIST DURING ULNA TO RADIAL DEVIATION

Abstract

The aim of this study was to investigate how the rotational axis of the wrist moves as the hand goes from full ulna to full radial deviation.

Fifty normal wrists in 25 subjects were assessed with a Polhemus Fastrak (TM) magnetic tracking system. The subjects, aged 19 to 57, placed their palms on a flat wooded stool. Sensors were attached over their 3rd metcarpal and distal radius. The sensors then recorded movement from ulna to radial deviation. The translational and rotational measurement accuracies were 1 mm and 1 degree respectively.

The mean range of movement was 45 degrees (SD 7). In ulna deviation the axis was in the region of the lunate. As the hand moved towards radial deviation, the axis moved distally. At the end of the movement the mean distal displacement was 21 mm (SD 15). In 32 wrists the distal displacement was accompanied by a mean displacement towards the ulna of 12 mm (SD 8). In 18 wrists the distal displacement was accompanied by a mean displacement towards the radius of 8 mm (SD 5).

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 types of carpal movement proposed by Craigen and Stanley (J. Hand Surg, 20B, 165–170, 1995).