For above-knee amputees, today's artificial knees are vast improvements over their counterparts of just a few years ago. But even these advanced prosthetics have limits: they can't adapt to a patient's natural way of walking or to changing terrain, like sudden steep hills or varying surfaces.

Researchers at MIT's Leg Laboratory in the Artificial Intelligence Laboratory have developed a prosthetic knee that can adjust to these situations. With built-in sensors, the device detects the position of the knee in space and all the forces applied to it. The sensors transmit the information to a microprocessor within the knee, which sends a signal to an actuator that modulates the knee's mechanical behavior. If a person fitted with the artificial knee moves from, say, cement to tall grass, the sensors detect that the knee has less forward speed and is no longer swinging as easily; the system then compensates for the change. The new device represents a dramatic improvement over the most sophisticated current system, which requires that users connect the knee to a separate computer each time they need to change its settings. Flex-Foot, a maker of leg prosthetics based in Aliso Viejo, CA, is commercializing the Leg Lab's electronic knee. The company hopes to have a product in beta trials next month.