Validity of motion analysis using the Kinect system to evaluate single leg stance in patients with hip disorders

Background: Abnormal movements during single leg stance in patients with hip disorders could be detected by the Kinect system as well as the three-dimensional motion analysis system. However, validity of the Kinect system to evaluate single leg stance in patients with hip disorders remains unknown. Research question: To investigate the concurrent validity of the Kinect system, relative to the VICON three-dimensional system which is considered as the gold standard for motion analysis, to measure trunk and pelvis alignment during single leg stance. To investigate the discriminant validity of the Kinect system between with and without hip disorders. Methods: For evaluation of the concurrent validity of the Kinect system, the intra-class correlation coefficient (ICC ((3,1))) was calculated for the angle of inclination of the pelvis and trunk in 5 healthy individuals. For evaluation of the discriminant validity of the Kinect system, the angle of inclination of the pelvis and trunk during single leg stance were measured in 27 individuals with hip disorders and 100 healthy individuals. Differences in the maximum angle of inclination of the pelvis and trunk were evaluated between hip disorders and healthy individuals using the Mann-Whitney U test. Results: ICC values were between 0.83-0.93 for the pelvic and 0.63-0.81 for the trunk angle, respectively. The maximum trunk inclination angle calculated using the Kinect system was significantly higher in patients with hip disorders than healthy individuals, with no significant between-group difference in the angle of inclination of the pelvis. Significance: The Kinect system was adequate to detect certain abnormal movements during single leg stance among patients with hip disorders. Therefore, the Kinect system could provide a convenient motion analysis tool for the assessment of patients with hip disorders.