Initial Test of Bionic Leg Brace Yields Rapid Results in Patients After Stroke

By Robin Hindery

UCSF clinical specialist Heather Brown adjusts the Tibion PK100 or PowerKnee for study participant Eric McHuron.

After suffering a stroke, many patients set goals as they work to regain functional independence, and progress is often measured in increments most of us take for granted: buttons on a shirt, words strung into sentences or limbs moving in harmony. For Vikki Harrigan, progress is measured by getting across the street before the red light flashes at the crosswalk that stretches across the four lanes of Geary Boulevard near her San Francisco home. “I know that I have to walk at a 2.2 [miles per hour] pace to get across Geary in time, and after 10 years, I can finally do it before the light changes,” said Harrigan, a UCSF patient whose stroke occurred in December 1998 when she was 48 years old. Harrigan attributes her recent breakthrough to four weeks of rehabilitation at UCSF’s Physical Therapy Health and Wellness Center, using a state-of-the-art bionic leg brace that supplements muscle strength and provides self-regulating mobility assistance.

Eric McHuron practices leg lifts with the Tibion PK100, a sort of robotic boot that inserts into the user’s shoe and extends up to mid-thigh.

The device, the Tibion PK100, or PowerKnee, is a sort of robotic boot that inserts into the user’s shoe and extends up to mid-thigh. It is equipped with multiple sensors and microprocessors that can detect the user’s actions – such as transitioning from sitting to standing, or climbing stairs – and adjust support and flexibility accordingly. “Basically, the device determines what the patient is trying to do and then assists in that action,” said Jean Nelson, vice president of marketing for Tibion, which is based at NASA Research Park in Moffett Field. “The computer’s learning algorithm allows it to adapt after the first few steps.” In addition to helping patients with neuromuscular impairment due to stroke, multiple sclerosis or Parkinson’s disease, Tibion designed the PK100 to serve individuals suffering from osteoarthritis or recovering from knee surgery. The battery-operated device can be personalized according to a user’s height, weight and physical needs. For example, the knee angle can be adjusted for those who don’t have full range of motion. The first commercial model of the PK100 was unveiled in February at a meeting of the American Physical Therapy Association in Las Vegas. UCSF is among the first places to test it out on physical therapy patients, Nelson said. Throughout the month of April, three or four times a week, Harrigan and two other patients in the chronic post-stroke phase worked with physical therapists in the health and wellness center and with representatives from Tibion to see whether the PK100 produced any noticeable improvements in their unassisted walking speed, stride length, balance and endurance.

Eric McHuron takes a break between exercises with his wife Carol.

“If this technology is going to work as an effective training tool, it has to have enable activities that are goal-directed, repetitive and progressed in difficulty,” said Nancy Byl, PT, PhD, professor emerita in the UCSF Department of Physical Therapy and Rehabilitation Science, who supervised the case study. The device also needs to be easy for patients to use on their own, without the assistance of a physical therapist, she said. After just four weeks, each of the UCSF patients reported significant improvements in their physical capabilities – and Byl’s stopwatch backed up those claims. Eric McHuron, who suffered a stroke in December 2003, shaved nearly seven seconds off his unassisted 10-meter walking pace after training with the PK100, Byl said. He also increased the distance he was able to walk over a six-minute period by more than 20 percent, from 170 meters to 207 meters. “This is a significant gain in only four weeks in a patient who is almost six years post-stroke,” Byl said. McHuron’s wife, Carol, said her husband uses his cane less frequently around the house since he started using the PK100. “He’s just gotten better all around, just this past month,” she said during the couple’s April 30 visit to the Physical Therapy Health and Wellness Center, located on UCSF’s Mission Bay campus. “He’s so excited to show me what he can do. He keeps saying, ‘Watch!’” McHuron’s newfound physical confidence was on full display on April 30 as he put the PK100 through a workout, laughing his way through wall sits and even taking a spin on the center’s elliptical trainer. “This has been so good for his mental as well as his physical health,” Carol McHuron said. “Rehabilitation is so important, and it’s forever.” Byl said she is constantly amazed by the gains patients can make even years after a stroke – gains she attributes in large part to neuroplasticity, the lifelong ability of the brain to reorganize neural pathways, based on new experiences. Patients after stroke can quickly develop poor form by avoiding the use of impaired limbs or using abnormal patterns of movement that are difficult to change. But through guided movements and repetitive use of those limbs, the brain can relearn how to incorporate them into everyday activities. New technology like the PK100 now enables patients to achieve the necessary learning-based repetitions to change neural processing, Byl said. “Patients are often discouraged after a stroke or brain injury, but there’s hope,” she said. “You might not be able to repair damaged neurons, but there are a lot of neurons you’ve never used before. The challenge is to learn to make new synaptic connections and recruit alternative neurons to perform the tasks compromised by the injury.

Nancy Byl, MPH, PhD, professor emeritus in Physical Therapy & Rehabilitation Science at UCSF, explains a device that measures movement resistance for study participant Victoria Harrigan, left.

“You may not be able to be the same as you were before the injury, but you can learn to be independent and restore quality of life despite the impairment,” she added. In a single month, the PK100 and the other forms of physical therapy Harrigan has received at UCSF have largely repaired the damage caused by 10 years of bad habits, she said. “Every day, little by little, I’m making changes and repatterning my brain,” she said. “After my stroke, I learned over time to cope and just do what I needed to do to get around. Now I’m learning to do it correctly.” Photos by Susan Merrell

Related Links:

UCSF Physical Therapy Health and Wellness Program at Mission Bay

Tibion Corporation

Harnessing the Brain’s Plasticity Key to Treating Neurological Damage
UCSF News Release, Feb. 15, 2007