Small Form Factor Technology Solves Complexities of Thought-Controlled Leg Prosthetics

Rehabilitation Institute of Chicago has developed the first neural-controlled bionic leg, using no nerve redirection surgery or implanted sensors. It’s a powerful advancement in prosthetics, including motorized knee and ankle, and control enabled by the patient’s own neural signals. Powered by a tiny but powerful Computer-on-Module platform, this thought-controlled prosthetic represents a significant breakthrough in medical embedded design, improving patients’ lives and mobility with a prosthetic that more closely than ever acts like a fully-functioning natural limb.

The technology of prosthetic limbs has come a long way over time, yet options are still limited for leg amputees. While simple peg legs have evolved to more sophisticated and realistic artificial limbs, the patient was forced to undergo nerve surgery or endure invasive implants. And even though the technology to produce through-controlled mechanized arms has existed for some time, the complexities of leg motion have kept it from being successfully applied in leg prosthetics. Without the ability to move and control the knee and ankle, the prosthetic leg remained a passive solution for patients struggling to replicate natural leg motion.

The Rehabilitation Institute of Chicago (RIC) has taken on this challenge, teaming with scientists at Nashville’s Vanderbilt University for the development and study of a “bionic leg,” or one with motorized joints at the knee and ankle. For five years, this team has explored computing technology and collected information on how people walk – ultimately building a much more advanced prosthetic leg that incorporates natural muscle signals for better control.

Dr. Levi Hargrove, director of Neural Engineering for RIC’s Prosthetics and Orthotics Laboratory, says, “Technology has developed to the point where we can have these motorized joints, or bionic limbs. The battery-operated motors themselves must be very powerful as they carry the body weight, yet they must be power-efficient as they drag power on every step. We’re fortunate to see these elements now available in very small form factor embedded technologies, allowing us to create a small, lightweight computing package that enables the leg. It’s the first of its kind, revolutionary in that the user does not need nerve surgery or implants to control movement.”

Enabled by Gumstix’ Overo Air computer-on-module (COM) product family, the bionic leg is able to deliver significantly greater control and motion to patients than previous prosthetic devices.

Enabling Bionics with Computer-on-Modules
Reliable, low power components are at the core of the bionic leg, which must also handle cutting edge algorithms that require flexible, high performance microprocessors. For example, the leg’s computer uses an algorithm to determine which muscles are being signaled to move and then commands the motors to move the joint. “The sensors in the leg are extremely responsive and come in direct contact with the skin, eliminating the need for implants yet detecting the tiny electrical signals sent by the muscles when they attempt to move,” said Hargrove.

The motors powering the bionic leg are based on Gumstix’ Overo computer-on-module (COM) product family, featuring flexible wireless communications in a very small package. For example, the Overo AirSTORM-Y COM, based on the 800 MHz Texas Instruments AM3703 Sitara applications processor, includes an access point mode, 802.11b/g/n Wi-Fi and Bluetooth 4.1 with BLE using TI's WiLink 8 wireless module. COMs work in conjunction with an expansion board containing the customization for the end-use application; scientists are able to further customize expansion boards utilizing web-based design-to-order tools such as Geppetto D2O, to meet the unique requirements of their embedded medical devices.

“We chose the Gumstix Overo Air because it blended small form factor performance with wireless connectivity and flexible data storage.  During the research and development phase, we wanted a full operating system – Linux was an excellent option, providing an extensive set of analytic, storage and networking tools, useful in managing development."

The on-board motors help push the patient up ramps and stairs – actually walking upstairs instead of being dragged by the patient. This offers a tremendous advantage in quality of life, reducing the amount of physical strain a patient endures when using a conventional prosthesis. Safety is improved as well, as fewer compensation motions are required; this adds long-term health value by preventing overuse injuries in the future. With each step, the leg’s computer learns and memorizes a patient’s gait, using that knowledge to anticipate knee bend, ankle flexion and foot strike.

Improving Life for Amputees
For embedded designers, the bionic leg is a chance to make a real difference with small form factor design. With high performance in a tiny platform, COMs-based technology is uniquely able to help mimic natural leg movement and improve the long-term quality of life for amputees.

“With intelligent engineering, we’re enabling a near-normal gait for amputees, who can now transition seamlessly between sitting, standing and walking, as well as ascending and descending stairs and ramps," said Hargrove. "This leg's intuitive thought control not only lets patients walk without thinking too much about it, it also works just as well without nerve redirection surgery or implants placed into the body. The patient base is no longer limited to those able or willing to have surgery or implants to control an artificial limb, and within a few years we will have the ability to help many more of the one million people in the U.S. with leg amputations."

Nearly five years in the making, the bionic leg is still in trials. But thanks to determined researchers and advances in small form factor platforms, research continues – with engineers monitoring patients’ movements as they practice walking with the leg and making adjustments to their gait and usage needs. RIC’s team of engineers and clinicians next must complete about one year of home trials, allowing them to continue studying how the leg works in different situations. RIC’s plan is to continue making improvements and soon make the life-changing prosthetic available for everyone.