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 rheumatoid arthritis affect function. Kinematic analyses using conventional six-degree-of-freedom characterizations are strongly coordinate-system depen dent and require careful interpretation. An alternative method, examining the motion in configuration space, permits identification of the number of degrees of freedom used to perform the motion. Radial-ulnar deviation movements of the wrist joint were tracked optoelectronically in a group of twenty-eight volunteers with rheumatoid arthritis, and an age- and gender-matched group of control subjects. Normal wrists demonstrated highly repeatable one-dimensional configuration spaces for five cycles of hand movement. Wrists affected by rheumatoid arthritis displayed more disorganized and two-dimensional configuration spaces. Two parameters from the configuration space trajectories were defined to quantify the range of motion (ROM) and amount of inconsistency or ‘jitter’ in the movement. Plots of jitter against ROM for the population of fifty-six subjects showed strong separation of the case and control groups, with rheumatoid wrists displaying lower ROM and higher jitter. These indices provide a simple means of quantifying differences between rheumatoid and normal wrists with minimal coordinate-system dependence.