Telerehabilitation is an emerging field of rehabilitation. Combining medicine and engineering, telerehabilitation provides an alternative method of rehabilitation therapy in areas lacking medical resources, and an easy way to resolve the inconvenience for the disabled patients to seek rehabilitation services. This study developed a device that integrates inertial measurement units (IMU) and an ankle foot orthosis (AFO) named AFO-IMU module. We further demonstrate the AFO-IMU module on telerehabilitation diagnostic including patients with muscle weakness due to brain injuries and patients who will receive total knee replacement surgery due to osteoarthritis of knee joints to determine the feasibility in clinical usage. The results from this study indicate that AFO-IMU module is a simple and effective telerehabilitation system to correctly assess knee joint activity and track knee joint rehabilitation diagnosis.