Knee injuries are common in people of all ages, due to physical activity and other reasons. In all cases, physical therapy is prescribed but it will depend on the type of injury suffered. Latest research in robotics has developed assistive devices to contribute to improving the patient's quality of life. In this paper, we propose a five-bars-linkage knee rehabilitation device, which is reconfigurable according to the patient's height. We present the kinematic modeling of the device to show that it can reproduce certain exercises or routines prescribed at physiotherapy during the knee rehabilitation according to a processor developed. For this, we show the corresponding workspace and the required mechanical configuration of the five-bars-linkage system. To validate the functionality of the processor and of the mechanism, we implement a real case routine performed by a healthy subject. We use the hip and knee angular positions to process them and show the feasibility of the system, obtaining and comparing the corresponding workspaces.