Validity and reliability of Kinect skeleton for measuring shoulder joint angles: A feasibility study

Objective: To test the reliability and validity of shoulder joint angle measurements from the Microsoft Kinect™ for virtual rehabilitation. Design: Test-retest reliability and concurrent validity, feasibility study. Setting: Motion analysis laboratory. Participants: A convenience sample of 10 healthy adults. Methods: Shoulder joint angle was assessed in four static poses, two trials for each pose, using: (1) the Kinect; (2) a three-dimensional motion analysis system; and (3) a clinical goniometer. All poses were captured with the Kinect from the frontal view. The two poses of shoulder flexion were also captured with the Kinect from the sagittal view. Main outcome measures: Absolute and relative test-retest reliability of the Kinect for the measurement of shoulder angle was determined in each pose with intraclass correlation coefficients (ICCs), standard error of the measure and minimal detectable change. The 95% limits of agreement (LOA) between the Kinect and the standard methods for measuring shoulder angle were computed to determine concurrent validity. Results: While the Kinect provided to be highly reliable (ICC 0.76-0.98) for measuring shoulder angle from the frontal view, the 95% LOA between the Kinect and the two measurement standards were greater than ±5° in all poses for both views. Conclusions: Before the Kinect is used to measure movements for virtual rehabilitation applications, it is imperative to understand its limitations in precision and accuracy for the measurement of specific joint motions.