Digital data acquisition of shoulder range of motion and arm motion smoothness using Kinect v2

Range of motion (ROM) is a clinically important parameter in evaluating joint function. However, dynamic evaluation to determine the quality of the arm motion using digitized measurement is often overlooked during clinical assessment. We evaluated the accuracy of Kinect v2 (Microsoft, Redmond, WA, USA) as a digital tool for measuring shoulder ROM objectively and proposed a concept of motion smoothness reflecting the quality of arm motion.

Ten male participants were included in a 2-stage experiment. First, shoulder ROM was measured in 4 static poses (flexion, abduction, external rotation, and internal rotation) with Kinect v2, a 3-dimensional (3D) motion analysis system, and goniometry. Second, participants performed a point-to-point arm motion as naturally as possible. Kinematic data were collected with Kinect v2 and the 3D motion analysis system and then postprocessed to acquire parameters related to motion smoothness, including peak to mean velocity ratio, acceleration to movement time ratio, and number of peaks.

Kinect v2 resulted in very good agreement of ROM measurement (r > 0.9) with the 3D motion analysis (95% limits of agreement < ±8°) compared with goniometry (95% limits of agreement < ±10°). Kinect v2 also showed a good correlation and agreement of measurement of motion quality parameters compared with the 3D motion analysis (peak to mean velocity ratio, acceleration to movement time ratio, and number of peaks: r = 0.769, discrepancy = ±0.1; r = 0.922, discrepancy = ±5%; and mean = 1 ± 0, respectively).

We show that Kinect v2 can be used as a reliable tool to measure shoulder ROM and arm motion smoothness.