A Wearable Device for Accurate Ankle Movement Evaluation

In this paper, two devices were designed to create an accurate sensor platform for distal lower extremity movement monitoring. This sensor platform is intended to facilitate later development of a smart ankle brace or to guide ankle joint rehabilitation. The first device, a scanning apparatus, includes a commercial 3D scanner (EinScan Pro) and it is designed to move the scanner around a subject's ankle, enabling the creation of a detailed 3D model of subject-specific anatomy with accuracy of 0.5 mm. This 3D model informs correct placement of sensors on the second device, the sensor platform. The sensor platform is equipped with two Inertial Measurement Units and a Micro-Controller Unit to monitor foot rotations around the subtalar and talocrural axes of the ankle. The reference IMU is placed on the tibia bone as the reference frame, while the measurement IMU is placed on the intermediate cuneiform, representing the moving frame of interest. A custom flexible printed circuit board was fabricated to integrate the IMUs and MCU and ensure comfortable usage of the device. The sensor platform enables efficient data collection with the ability of wireless streaming to MATLAB, where the data is formatted for the OpenSense module of OpenSim. Both qualitative and quantitative validations were performed for ankle rotation angles and the measurement error was calculated to be 2.43° ±0.27° across three replications, each consisting of 120-second trials, with a peak-to-peak mean angle measurement error equal to 0.728°. Results of motion tracking and simulations are available at https://youtu.be/i24nhEXNHkw.