Asymmetric dynamic center-of-pressure in Parkinson's disease

Gait disturbance gradually worsens as Parkinson's disease (PD) progresses, which significantly affects the quality of life of PD patients. Treadmill-based gait analysis systems can measure gait parameters including the dynamic center-of-pressure (COP) trajectory during ambulation. In this study, we hypothesized that altered dynamic COP changes are new gait characteristics for PD patients.

Dynamic COP parameters and classic spatiotemporal parameters were obtained for each patient using a treadmill-based system at the maximal comfortable treadmill speed (MCTS). We compared dynamic COP parameters between 44 PD patients and 31 controls, correlated these parameters with clinical and spatiotemporal data, and adjusted for age and MCTS to determine whether the parameters were independent from the treadmill speed. We also evaluated characteristics of COP parameters in relation to the more and less affected sides in PD patients.

During treadmill walking the length of the COP trajectory in the stance phase was decreased, an effect that was more prominent on the more affected side in PD patients. COP parameters related to this change were significantly altered in patients when compared to controls. Asymmetry of the COP trajectories compared between both feet was identified as a significant gait characteristic after adjusting for age and MCTS. The overlaid graphical display of dynamic COP trajectory in PD patients showed "distorted butterfly with asymmetric wing" feature.

Dynamic COP asymmetry provides a new and intuitive way to analyze gait abnormalities of PD patients. Further studies with prospective designs will substantiate the clinical usefulness of this feature of gait.