Agreement between an electrogoniometer and motion analysis system measuring angular velocity of the knee during walking after stroke

Abstract

Objectives There is a need to measure quality of movement to assess effectiveness of physical therapy interventions after stroke. Knee angular velocity may be a sensitive measure of change in performance of movement during functional activity, but not all clinical centres have access to a movement analysis laboratory. The aim of this study was to investigate the concurrent validity of using an electrogoniometer and a laboratory-based movement analysis system (Vicon Motion Systems Ltd, Oxford, UK) to measure knee angular velocity. Design Prospective agreement study. Setting Movement analysis laboratory. Participants Fifteen adult volunteers (mean age 55.6 years) at least 6 months after stroke and able to walk at least 4.5 m indoors. Interventions Kinematic data were collected simultaneously from the electrogoniometer and the Vicon system whist subjects walked forwards in the laboratory. Main outcome measures Electrogoniometer and Vicon data were filtered using a second-order Butterworth filter. Angular velocity was calculated for both sets of data, and the values for peak flexion and peak extension velocity for each stride were extracted for each subject trial. Results The intraclass correlation coefficient (ICC) and lower 95% confidence interval was 0.90 (0.87) for peak flexion angular velocity and 0.92 (0.89) for peak extension angular velocity. The limits of agreement were −50.64 to 80.28 °/second for peak flexion angular velocity and −30.59 to 86.27 °/second for peak extension angular velocity. Conclusions Despite high ICC values, the limits of agreement were wide. These data indicate that the Vicon system and an electrogoniometer may not be used interchangeably to measure knee angular velocity in stroke subjects.