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Walk This Way

Posted November 19, 2012

You were taught to read and write. You were taught to do arithmetic. But chances are, you taught yourself to walk. And quite possibly you got it wrong, and are now walking in a way that could damage your hips. If that’s the case, says Cara Lewis, an expert on gait and the musculoskeletal causes of hip pain, you could be the recipient of one of the 250,000 hip replacements that are performed in this country each year. Lewis is developing methods- including a robotic device – to teach people how to correct a hip-battering walk.

“My goal is to intervene early on, so that osteoarthritis doesn’t progress—or doesn’t even develop,” says the Sargent College of Health & Rehabilitation Sciences assistant professor of physical therapy.

Lewis has been honored for her research with a Peter Paul Career Development Professorship (see sidebar below), and with a $275,000 grant from the National Institutes of Health.

Her research has convinced her that hip pain can’t be written off as a burden of old age. That wouldn’t explain the increasing number of young people, especially runners and other athletes, who suffer from acetabular labral tears, an injury to cartilage in the hip socket that increases the risk of developing arthritis.

The repetitive stress from an improper gait, Lewis believes, will cause hip pain, “which then progresses to a labral tear; you then start losing stability in the joint, which then leads to the arthritis—which [may result in the need for] a hip replacement. The replacement might be happening when you’re 60, but it’s because of something you did when you were 30.”

The 20- and 30-somethings are the population to target. “If you change the way they’re walking now, you can change their pain after they already have a tear—or maybe change it before they get the tear,” she says.


For Lewis, the answer came at the University of Michigan, Ann Arbor, where she did postdoctoral work on robotic exoskeletons for the ankle joints. She built a robotic orthosis, a pneumatically powered exoskeleton consisting of a brace each for the waist and two legs.

In a newly built lab at Sargent College, where Lewis has been teaching since fall 2009, healthy subjects wear the orthosis while walking on a custom treadmill with two plates measuring force separately for the left foot and the right foot. Electrodes on their legs record their muscle activity. And they are covered in reflective markers monitored by several motion-capture cameras.

“The computer system picks up the marker positions and then can re-create a model of the skeleton,” she says. “From that we can tell differences in angles and figure out when we want to apply the robotic force, and how much.”

When the subjects exhibit what Lewis calls “the lazy walk”—straining their hips by using them to swing one leg forward while the other leg lags far behind—she presses a button. Air from a large pressurized air tank bursts into the orthotic actuators and corrects their gait.

“It’ll start bringing your leg forward sooner,” Lewis says. “It keeps you out of that bad position. I can wean people off of the bad position and they can walk normally on the street.”

Lewis has also had success correcting lab subjects’ gait with decidedly low-tech verbal cues. “Some of it is just saying, ‘Hey! The way you walk doesn’t work; push more with your foot!’” Lewis says with a laugh. “Or ‘Change your posture’ or ‘Take shorter steps.’”

Lewis’ lab is now focusing on research, rather than intervention, but she envisions a time when her systems are put to work in clinics. People recovering from hip injuries could work out on the treadmill until they trained themselves to walk properly. And healthy people could use the orthosis to improve their walking and prevent a hip injury.

Source: Boston University, story by Patrick L. Kennedy

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