CONFIGURATION-SPACE ANALYSIS OF THE RHEUMATOID WRIST

Three-dimensional analysis of joint motion in vivo provides a tool for assessing the extent to which pathological conditions such as rheumat oid arthritis affect function. Kinematic analyses using conventional s ix-degree-of-freedom characterizations are strongly coordinate-system dependent and require careful interpretation. An alternative method, e xamining the motion in configuration space, permits identification of the number of degrees of freedom used to perform the motion. Radial-ul nar deviation movements of the wrist joint were tracked optoelectronic ally in a group of twenty-eight volunteers with rheumatoid arthritis, and an age- and gender-matched group of control subjects. Normal wrist s demonstrated highly repeatable one-dimensional configuration spaces for five cycles of hand movement. Wrists affected by rheumatoid arthri tis displayed more disorganized and two-dimensional configuration spac es. Two parameters from the configuration space trajectories were defi ned to quantify the range of motion (ROM) and amount of inconsistency or 'jitter' in the movement. Plots of jitter against ROM for the popul ation of fifty-six subjects showed strong separation of the case and c ontrol groups, with rheumatoid wrists displaying lower ROM and higher jitter. These indices provide a simple means of quantifying difference s between rheumatoid and normal wrists with minimal coordinate-system dependence.