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Science & Tech

The Race for a Nimble Old Age

SAR prof gets a Peter Paul award for robotic walking device


The graphic representation of a patient’s skeleton is generated by a special computer program in the lab of Cara Lewis (right), a SAR assistant professor of physical therapy. Photos by Vernon Doucette and Kalman Zabarsky

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 all wrong. Sure, you get from point A to point B. But you might also be damaging your hips. As a result, you could be on track to needing a hip replacement someday, according to Cara Lewis, an expert on gait and the musculoskeletal causes of hip pain. Fortunately, she’s built a robotic device that can be used to teach both the healthy and the injured 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 was honored last month for her research with one of four Peter T. Paul Career Development Professorships. Other honorees are Pietro Cottone (top, right), a School of Medicine assistant professor, who uses integrative molecular biological, pharmacological, quantitative, and behavioral methods to study the neurobiology of food intake, addiction, and stress; Simon Rabinovitch (middle, right), a College of Arts & Sciences assistant professor of modern Jewish history; and Delvon Parker (lower, right), a School of Management assistant professor of operations and technology management, whose main research interests include product modularity, supply chain management, and production system complexity.

The Peter Paul awards recognize outstanding young faculty within the first two years of their BU appointment, and provides $40,000 a year for three years in salary support and research funds. They were established in 2006 with a gift from entrepreneur, philanthropist, and BU trustee Peter T. Paul (GSM’71), president of the mortgage banking company Paul Financial, LLC, who gave the University $1.5 million to fund 10 professorships over five years.

“There are a lot of questions in physical therapy that we don’t know the answers to, like why one treatment works and another doesn’t,” says Lewis. “The Peter Paul professorship will give me more time and money to get the pilot data, so that I can compete for larger funding opportunities.”

Lewis’ research has convinced her that hip pain can’t be written off as a burden of old age, a sign of wear and tear. That wouldn’t explain the increasing number of young people, especially runners and other athletes, who are now being diagnosed with acetabular labral tears. A source of hip pain that has been recognized only recently, labral tears heighten the risk of developing arthritis in the hip earlier than expected, says Lewis.

The labrum is a ring of fibrocartilage attached to the rim of the acetabulum, the hip socket in which the femur sits. “The labrum is some of the tissue that helps add stability, similar to that in the shoulder,” she says.

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. So “identifying the people who are at risk for the tear and changing their mechanics,” is the way to go.

But how do you change the mechanics of a person’s gait?

For Lewis, the answer came at the University of Michigan, Ann Arbor, where she did postdoctoral work on robotic exoskeletons for the ankle joints. “Because of advancements in orthotic materials, in actuator technology,” she explains, “we were able to finally move the technology to doing work at the hip joint.”

She built a robotic orthosis, a pneumatically powered exoskeleton consisting of a brace each for the waist and two legs. An orthosis is any device that supports or corrects limb or torso movement; splints and arch supports are orthoses.

“She’s in virgin territory,” says former Michigan colleague and kinesiology expert Dan Ferris. “She’s using an orthosis for motor retraining rather than for assistive technology. That’s what’s novel.”

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.”

That means when 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, “so it keeps you out of that bad position” more effectively than verbal direction does.

Then, “because I have such precise control over the timing and amount of assistance, I can wean people off of the bad position,” she says. “And then they can walk normally on the street.”

Currently the lab is doing research, not intervention. But Lewis envisions a time when this system is replicated in clinics all over. If you were recovering from a hip injury, you could visit a clinic regularly to work out on the treadmill until you’d trained yourself to walk better. Furthermore, she hopes, healthy people could use the orthosis to prevent a hip injury from happening.

No one can say whether this will work, because no one has ever tried it, says Ferris. But if anyone can pull it off, it’s Lewis. “Most physical therapists—in fact, virtually all—do not have the level of technical understanding in terms of quantitative biomechanical analysis that she does,” Ferris says. “She has a unique background that’s going to really set her up for success regardless of what project she undertakes.”

Patrick Kennedy can be reached at plk@bu.edu.

This article originally appeared in the Fall 2010 issue of Inside Sargent.

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