Digital testing device to measure the active range of motion of finger joints using an RGB-D camera

Range of motion (ROM) is an essential index for assessing the effectiveness of therapeutics in clinical practice. Rehabilitation therapists commonly use a goniometer to manually measure the ROM of finger joints. However, the measurement could be time consuming and burdening for patients, particularly when multiple finger joints are required to be measured. The required measurement accuracies of general rehabilitation and hand therapy tests are less than 5° and 2°, respectively. Therefore, in this study, we developed an active ROM digital testing device to reduce the measurement time and ease the burden on both patients and rehabilitation therapists during the measurement. The proposed digital testing device comprises an Intel RealSense depth camera and a computer. Rehabilitation therapists point the camera toward the patient’s finger joints to capture the RGB and depth images. Similar to the measurement principle of the goniometer, the target joint angle can be computed by obtaining the three-dimensional coordinates of the point cloud on the centerline of the finger bones that form the joint and the center point of the joint. The effectiveness of the proposed device was verified by comparing the generated results with those obtained from the goniometer. In 91.7% of the trials conducted in this study, the error of the proposed digital testing device was found to be less than 2° with a mean measurement time of 4.9 s, which is 46.2% less that of the goniometer.