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

Abstract

Aim: The carpal bone arrangement can be described as a matrix of two rows and three columns. There a various theories as to how the bones within the matrix move during ulna to radial deviation. One theory suggests that there are two types of wrist movement, namely Row & Column¹.

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

Materials and Methods: Ulna to radial deviation was assessed in 50 normal wrists in 25 normal subjects aged 19 to 57. 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 metcarpal 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 45 degrees (SD 7). In full ulna deviation the wrist rotational 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 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).

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 types of carpal movement. i.e. Column movers and row movers¹.