Continuous passive motion (CPM) and continuous active motion (CAM) physiotherapy devices are commonly used to promote rehabilitation of damaged synovial joints. CAM devices use some form of mechanical resistance to patient muscle activity. This paper presents a combined CAM/CPM device which functions conventionally in the CPM mode, but in the CAM mode uses the motor to exert a constant force against patient activity, simulating the effect of a spring load. In the CAM mode, the motor is embedded in a feedback loop with two sensors, one a force sensor, the other an angular position sensor. The PC provides full recording and graphic display of the patient?s force and, angular position of the device and motor force. The simulated-spring-load system operation is smooth and natural. The presented design will be of use for diagnosis, therapy and research.