Kinematic approach to gait analysis in patients with rheumatoid arthritis involving the knee joint.

OBJECTIVE To analyze abnormal gait patterns in patients with rheumatoid arthritis involving the knee joint. METHODS In 2 patient groups with rheumatoid arthritis, changes in relevant angular parameters in the sagittal plane were analyzed by an electromagnetic tracking instrument. One group consisted of patients with knee joint involvement and severe inflammation without progressive destruction; the other group had knee joint involvement with progressive destruction and low disease activity. Knee angle was measured as the projected angle in the sagittal plane formed by 3 sensors (hip-knee-ankle); the changing mean angle, angular velocity, and angular acceleration were displayed. Furthermore, the angle formed by the vector element's endpoints for each sensor's displacement (designated alpha angle) was measured continuously. RESULTS Compared with age-matched controls, patients with severe inflammatory knee joint involvement showed limitation of alpha angle change in the stance phase, and patients with knee joint destruction had shortened swing phase duration and decreased alpha angle change in the swing phase. A sharpened alpha angular velocity change curve was observed in the latter. Characteristic differences between groups with inflammation and destruction were more clearly evident from the alpha angle than from the knee angle itself. CONCLUSION We observed gait differences between rheumatoid arthritis patients with active inflammatory arthritic knee joint involvement without progressive destruction and those with joint destruction and minimal inflammation. Features of gait disturbance in rheumatoid arthritis were not simple, even with a single major site. Therefore, techniques such as biokinetic gait analysis can provide practical information about functional joint integrity in this patient population that could aid in therapeutic decision making.