Knee Joint Angle Measurement during Running by Bending Angle Sensor Attached to Loose-fitting Clothing

<p>Anterior cruciate ligament (ACL) injuries and reconstruction surgeries result in changes in the knee joint kinematics, necessitating improvements of the movement pattern of the injured knee joint via monitoring of the knee joint movement pattern. Visual estimation does not afford satisfactory accuracy during walking and running. Furthermore, three-dimensional (3D) motion capture devices using cameras have limited measurement ranges. These problems can be solved by wearable sensors. However, for consistent accuracy, wearable sensors need to be fixed to straps, tapes, or skin-tight garments. Straps and tapes may interfere with movement, while skin-tight garments may be difficult for patients with joint problems to wear. The attachment of existing wearable sensors to loose-fitting clothes has resulted in the reduction of the measurement accuracy. Therefore, this study aims to develop a bending angle sensor that can be attached to loose-fitting garments and to determine whether it has sufficient accuracy for monitoring knee joint motion patterns, especially during running rehabilitation after an ACL injury or a reconstruction surgery. The subjects were twenty healthy adult males who wore loose-fitting garments with the bending angle sensor attached to the right knee. They performed running tasks on a treadmill at speeds of 8, 10, and 12km/h for 90 s. The right knee joint motion was simultaneously measured with a 3D motion capture device and the bending angle sensor. The data for 60 s, excluding the 15 s after the start and before the end, were compared:MAE=5.8±1.1°, RMSE=7.0±1.4°, and R²=0.94±0.02. The results show that loose-fitting clothes attached to the bending angle sensor enables monitoring of the knee joint motion during running rehabilitation.</p>