## 1 Introduction  
Early rehabilitation training is important to patients who have undergone lower limb surgery, which can speed up the recovery of limb function, greatly reduce the rehabilitation process, and effectively prevent the occurrence of postoperative complications [1; 2]. However, early postoperative rehabilitation training techniques are limited for the lack of sensor and evaluation methods. For example, all patients should be recumbent for a certain period of time after surgery to prevent from secondary injury in China. Another problem of this method is that it may bring about complications such as venous thrombosis and more serious consequences [3]. Thus, it has become a major challenge to select a suitable method for early sensor technique and evaluation of effectiveness after surgery to ensure better recovery of patients. Studies have shown that the health condition of a persons' lower limbs can be reflected by the persons' gait characteristics and plantar pressure distribution [4; 5; 6]. There are certain laws in the distribution of healthy persons' plantar pressure. Deformity and abnormal function will destroy the normal distribution of plantar pressure, showing different distribution laws [7]. Therefore, it is of great value to evaluate the rehabilitation effect of patients by combining rehabilitation training with plantar pressure.  
Moreover, most of the traditional patterns of lower limb postoperative rehabilitation training adopt physician-assisted manual training or gait rehabilitation robot assisted training, which is confined to hospital or nursing sites, and at least one physician or nurse is needed [8; 9; 10]. With the increase of postoperative patients, the current shortage of medical resources and professional rehabilitation physicians is obviously not satisfactory, and the medical costs are high [11; 12; 13]. Thus, more and more attention has been paid to the mode of treatment in the hospital and rehabilitation out of hospitals [14; 15; 16]. Currently, by using the plantar pressure with current telemedicine, some rehabilitation processes in the hospital can be transferred to communities or families by setting up a powerful information database. More importantly, it can improve medical efficiency and reduce the medical cost, but the information interaction between patients and doctors is a main challenge in this mode. With the development of \"medical + internet\" technology, researchers have done much work with tele-medicine methods [17; 18]. In this study, an Android mobile phone application (app) is designed, through which information between patients and doctors can be transmitted immediately, such as downloading training plans to patients, uploading training data to doctors. Patients can also learn about their own training status, such as the training phase and training effect. In addition, patients can communicate with doctors via various ways such as voice, small video, and internet messaging, realizing the rehabilitation mode for the patient out of hospital and greatly reducing hospitalization time to compensate for inconvenience caused by the current shortage and imbalance of distribution of medical resources.