The Hybrid Knee Prosthesis is a lightweight, versatile prosthetic knee with a unique hybrid design. The RIC Hybrid Knee uses a motor, transmission, and control system only for activities that require power, such as climbing stairs. When a person has to perform less difficult activities, such as standing or walking, the motor and transmission are disconnected. By strategically providing power only when needed, this unique hybrid configuration allows the prosthetic knee to be very lightweight and quiet (so you don’t sound like Robocop!). A user can also walk when the battery runs out, which you cannot do with any current powered prostheses.
Currently no other commercially available prosthetic knee can switch between passive and powered modes – you must choose between one device or the other, which both have benefits and disadvantages.
Passive prosthetic knees (which don’t use electrical energy, and are designed using a standard spring/damper system) are lightweight, functional, and quiet, but they are not ideal for completing challenging tasks. For example, when climbing up the stairs with a passive knee, you would have to step one leg at a time. Oftentimes, persons with lower-limb loss who use these types of devices may have to exert more energy and may become fatigued quickly.
On the other hand, powered prostheses provide some assistance for challenging walking tasks. While there have been numerous advances in powered prosthetic legs recently, these devices are significantly heavier than passive prostheses and are also much louder, due to the fact that these devices require a large motor for efficiency. A person who uses a powered prosthetic knee/leg may also constantly worry about losing battery power quickly.
The Hybrid Knee will combine the best of both of these worlds, provide intuitive control, and will also allow users freedom in having two operating modes available. In particular, its ability to adjust to allow for more force or speed is a unique component to prosthetic limbs, as its ability to operate in passive mode when a person does not need additional assistance. Finally, the device is roughly ½ the weight of currently available powered knees, making it the lightest powered knee to date.
This prosthesis will benefit persons with above-knee or knee-disarticulation amputation (when you retain full length of the femur bone). It will be especially useful for the elderly, or individuals who are smaller/weaker and may not be able to use a heavy prosthetic device.
In the final version, the goal is for the device’s control system to automatically sense when it should operate in passive mode, and when it should operate in active mode. This will allow for seamless transitions and will save battery life.
There are close to 1 million lower-limb amputees living in the United States—a population expected to double by 2050. Amputation above the knee is especially challenging. Research has found that above-knee amputees expend approximately 60% more energy during ambulation compared to able-bodied persons. These individuals are also more prone to joint disorders and chronic pain. The Hybrid Knee will especially benefit these persons by providing them with a lightweight prosthetic option that meets their daily needs and helps them maintain mobility.
Tommaso Lenzi, PhD, Assistant Director, Mechanical Engineering, The University of Utah. Dr. Lenzi is a former post-doctoral fellow and research scientist who developed the Hybrid Knee in collaboration with Dr. Levi Hargrove.