In a non-weight-bearing environment, transfemoral amputees demonstrated the ability to control a motorized powered knee and virtual ankle, according to recent study results.

In a previous study published in 2011, Levi J. Hargrove, PhD, director of the Neural Engineering for Prosthetics and Orthotics Laboratory at the Rehabilitation Institute of Chicago, and colleagues detailed results of transfemoral patients’ abilities to control a knee and an ankle in a virtual environment.

“What we wanted to do was test a few more transfemoral amputees,” Hargrove said. “We also wanted to try controlling a motorized knee as well. We didn’t have a motorized ankle at the time we completed this present study, so we just tested the amputees’ ability to control a motorized knee, as well as an ankle in a virtual environment.”

Synergistic muscle activation

Between September 2009 and September 2011, researchers performed two sets of experiments at the Rehabilitation Institute of Chicago. In the first component, researchers developed an offline data collection procedure where a pattern recognition system was trained and the offline classification accuracy of the system was computed. Six participants with unilateral transfemoral amputations and six healthy controls were not provided real-time feedback and attempted to move their phantom limb as instructed by a photograph displayed on a computer screen during this component. In the second component, three of the six transfemoral amputee participants returned to participate in a motion test where they controlled a virtual or physical prosthesis in real time.

Study results showed that, using only myoelectric signals measured from nine residual muscles in the thigh, sagittal plane motions of the knee and ankle were accurately recognized and controlled in both a virtual environment and on the actuated transfemoral prosthesis. The researchers also found that participants had accurate control of both the femoral and tibial rotation degrees of freedom within the virtual environment. Researchers also found that only five residual thigh muscles are required to achieve accurate control.

“Since the muscles that control the knee are largely still remaining after a transfemoral amputation, we were expecting the amputees to be able to control the knee. However, we were surprised with how well transfemoral amputees could control the ankle even though the muscles that primarily control the ankle are located below the knee,” Hargrove said. “We think there is some sort of synergistic muscle activation so they have these patterns that remain from when they previously controlled their ankle that we can measure from the quadriceps and hamstrings and other muscles that are above the knee.”

Hargrove told O&P Business News that transfemoral amputees have the ability to control knees and ankles using EMG signals in non-weight-bearing 
circumstances.

“We certainly need to do more work to transition this to weight-bearing or ambulation, but these results show that it certainly is possible to control knees and ankles when transfemoral amputees are in a seated position,” Hargrove said.

Future studies

Hargrove and colleagues are continuing their research by investigating how they can improve powered lower limb devices. The researchers are extending their work to include walking, stair climbing and walking on slopes, which is where they believe the future of research will go.

“It’s preliminary at this point, but I think within the year we’ll have some exciting results to share,” Hargrove said. “These powered lower limb devices are becoming more available and if we develop new and better control systems we will be able to provide more capability for the patients.” — by Casey Murphy