By Annette M. Boyle
BALTIMORE – If practice makes perfect, then stroke patients at the VA Maryland Health Care System in Baltimore should have a great boost in relearning the ideal walking gait, with some help from the Anklebot.
The device allows patients to move their ankles with a robotic “coach” 1,000 times in a typical therapy session rather than the 80 times patients working only with a human physical therapist would experience.
“The Anklebot doesn’t experience fatigue the way a physical therapist does, so patients can perform many more movements each session,” said Neville J. Hogan, PhD, director of the Newman laboratory for biomechanics and human rehabilitation and a professor at the Massachusetts Institute of Technology.
Improving walking in patients who have hemiparetic gait following stroke has long-term benefits. More than 70% of patients fall within the first six months following a stroke as a result of gait or balance issues, increasing the risk of potentially devastating hip fractures and other injuries.
The Anklebot is an exoskeletal robotic system that can move a patient’s foot in a full range of motion. Mounted on a knee brace and connected to a specially designed shoe that uses switchplates to measure the force, direction and angle of movement, the Anklebot provides a modulated boost to get the foot moving correctly.
In seated therapy, the patient responds to a visual display by trying to move the foot to a certain point to play a video game. “If they can’t make the movement at all, the robot will push them in the right direction. If they can initiate, even just a tiny movement, even in the wrong direction, the robot will guide them to the proper position,” Hogan said.
The technology “permits the patient to do as much as he can, then, as in coaching, helps them improve by using a built-in algorithm to progressively raise the bar,” Hogan told U.S. Medicine. Over time, the Anklebot offers less assistance while increasing the speed and number of movements the patient must perform.
As with passive-motion machines that simply rotate patients’ feet through the range of motion, the Anklebot improves joint mobility. Unlike them, it also improves function. “That was the first of the surprises,” Hogan said. “The first study at the Baltimore VA showed that even this form of treatment [seated] increased overall walking speed.”
That six-week study engaged eight veterans with hemiparetic gait deficits following a stroke in seated training with the Anklebot. Participants experienced a 20% increase in walking speed and significant gains in ankle motor control. In comparison, the researchers found in previous studies that it took six months of treadmill exercise alone to improve walking speeds by 17%. The increase in speed among the robotic-device users translated into greater independence and mobility for the participants, half of whom became community or limited community walkers.1
Another study by the same group, led by Larry W. Forrester, PhD, director of human motor performance laboratory at the Baltimore VAMC and a research associate professor in physical therapy and rehabilitation science and neurology at the University of Maryland School of Medicine, found that stroke patients who used the Anklebot during early sub-acute hospitalization following a stroke experienced significantly greater improvements in temporal symmetry, step-length symmetry and ankle control compared to patients receiving passive manual stretching. Both groups saw improvements in walking speed. The study appeared in Neurorehabilitation and Neural Repair in February.2
This past fall, the researchers stepped up the use of the Anklebot to see whether they could further improve gait in stroke survivors by getting patients to stand and walk with the device. “It’s way too early for us to draw concrete conclusions, but initial results suggest that repeatedly walking on a treadmill with the Anklebot may improve independent gait velocity and forward propulsion by improving ankle control at key times during walking,” Forrester said.
Study participants use the robotic device on a treadmill for 40 minutes three times a week. Already, “many of our study participants are telling us that Anklebot is really helping them,” Forrester said.
Improving ankle control has a direct bearing on gait and stability. “Normal walking is essentially controlled falling,” Hogan said. “What happens when you stop is what matters. How do you control the fall? You move your foot. How do you control the foot? You control the ankle. Stroke patients have stiffer ankles than other people. The Anklebot resolves the stiffness and leads to walking faster.”
The robot uses electrodes to determine the stiffness of the ankle by measuring the angular displacement and torque at the joint as it goes through the movements in therapy. As flexibility increases, it changes the force used to assist move the foot through its paces.
A significant part of the improvement in walking comes from rewiring the brain, in addition to relaxing and retraining the ankle. “In stroke, some part of the brain is starved of oxygen, and that creates a ‘hole in the brain.’” But that hole can be repaired or overcome in some cases by repeated actions, Hogan explained.
“Hebb’s Law states that ‘neurons that fire together, wire together,’ so when a patient responds to a visual display by attempting to move the foot and achieves something approximating the right movement with robotic assistance, the neural information comes back up to the brain at about the right time to reinforce that good response,” Hogan said. The more that happens, the stronger the neural connections and the faster the response becomes. The muscular movement and the intent reinforce each other. To get the full benefit, “the patient must be intentionally involved,” he added.
The Anklebot is also being used in research at the West Haven, CT, VAMC.
1Forrester LW, Roy A, Krebs HI, Macko RF. Ankle training with a robotic device improves hemiparetic gait after a stroke. Neurorehabil Neural Repair. 2011 May;25(4):369-77.
2Forrester LW, Roy A, Krywonis A, Kehs G, Krebs HI, Macko RF. Modular Ankle Robotics Training in Early Subacute Stroke: A Randomized Controlled Pilot Study. Neurorehabil Neural Repair. 2014 Feb 10. [Epub ahead of print]
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