New Amputation Procedure Allows Prosthesis to Be Controlled by Brain Waves

Ewing takes his first steps with a prosthesis. Photograph courtesy of Brigham and Women's Hospital, Communications and Public Affairs.

Earlier this year, Jim Ewing, 52, underwent a first-of-its-kind, experimental surgical procedure to amputate his lower left leg at Brigham and Women's Faulkner Hospital, Boston. If successful, the surgery will enable him to perform complex actions and feel sensation by allowing his brain to interact with a robotic prosthesis. The hospital held a news conference on November 21 to share these developments, which included images of the patient walking with a conventional prosthetic leg.

In December 2014, Ewing was rock climbing in the Cayman Islands with some friends and his daughter when he fell about 50 feet to the ground. Among the many injuries he sustained were a shattered ankle and a hole in his heel. Physicians told him that the likelihood of his injuries healing properly, if at all, were very small. "Every step hurt," Ewing said. Given the constant pain and nerve damage, he opted for amputation. He also reached out to Hugh Herr, PhD, a fellow rock climber he had met 30 years before.

Herr, an associate professor of media arts and sciences at the Massachusetts Institute of Technology (MIT), told Ewing about the work he was doing with next-generation prostheses, and introduced him to Matthew J. Carty, MD, director of the Brigham and Women's Faulkner Hospital Lower Extremity Transplant Program. McCarty had developed a new surgical procedure, dynamic-modeling amputation, now called the Ewing Amputation. During surgery, tendon pulleys are created over the tibia to relink the opposing muscles on the leg. This preserves the normal signaling between the muscles and brain, and will allow the use of next-generation prostheses that are capable of natural ankle movement and provide the user with prosthetic control and proprioception. The surgery was a collaborative effort with plastic, orthopedic, and vascular surgeons at the hospital, and involved biomechatronics experts from the MIT Media Lab, which Herr leads. Herr and his colleagues built a new bionic leg for Ewing.

"Motors and sensors on board the device enable the leg to move through the same type of motion that exist in the natural leg," explained Tyler Clites, a doctoral candidate with the MIT Media Lab. "This means that Jim will be able to point and flex his prosthetic toes as well as turn his ankle in and out.... This versatility goes far beyond the motion that is available in existing devices."

The next phase will be connecting the prosthetic leg to Ewing's nervous system, Clites said. They have started to evaluate the muscles in Ewing's residual limb and to put a system in place to communicate with the electrical activity in his muscles. The team is using sensors that are placed on Ewing's residual limb to capture and transmit the electrical activity from his muscles. Different electrical activity is received from each of the four muscles, which, with this surgery, allows them to connect each of those muscles signals to a different motion on the prosthesis; in a traditional amputation, the signals typically overlap.) This advancement is a result of the surgery and rehabilitation protocol, Clites said.

Over the next several months, Ewing will be implanted with implanted myoelectric sensors (IMES) []developed by the Alfred Mann Foundation, and then fitted with the prosthesis. The IMES will be injected into Ewing's leg muscles and replace external sensors that are being used during the initial testing phase. "Then, experiments will begin to evaluate his independent control over all the different motions and they will be compared to someone who has had a traditional amputation," Clites said.

Additional improvements are planned for the prosthesis, such as extending the battery life, increasing the amount of power to the leg, and reducing the noise, as well as adding a joint to help with push-off. Development of a knee joint is also planned so the team can start exploring applications of the surgery to patients with transfemoral amputations, Clites added.

"Jim represents a proof of concept and a best-case scenario in which we still have a lot to work with," said Carty. "We have, through the course of developing the idea underlying Jim's procedure, thought of iterations of this that would be applicable to folks who have already experienced limb loss." He added that this technique should be applicable for either a lower-limb or an upper-limb amputation.

Editor's note: This story was adapted from materials provided by Brigham and Women's Faulkner Hospital.