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Watch the way you walk

By Kay Lazar
Globe Staff / October 17, 2011

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Cara L. Lewis often has to squelch the urge to jump in front of people who are walking or running by her and yell “Stop! Do you realize the damage you are doing to your hips?’’

The 40-year-old assistant professor of physical therapy at Boston University’s Sargent College - a runner herself - is in a race to spare members of a younger generation from the joint pains of their parents.

Lewis studies the way people walk and believes that if they can learn how to move properly, taking the stress off their hips, they may avoid the injuries and joint deterioration that often lead to a hip replacement down the road.

She’s got company.

As the number of Americans undergoing hip and knee replacements steadily increases, a growing number of researchers are searching for ways to head off damage to these pivotal joints.

Surgeons are replacing 320,000 hips and more than 670,000 knees each year, according to the federal government’s latest count, and the numbers are expected to mushroom over the next two decades.

Many of these patients are hobbled by osteoarthritis, a disease that typically worsens with age and wears down the cartilage that cushions the bones in joints.

At least 67 million adults - a quarter of the adult population - will have arthritis by the year 2030, according to government projections, and most will have osteoarthritis.

The legions in pain could be even higher, disease trackers warn, because of the growing number of younger overweight Americans. Excessive weight is a major risk factor for osteoarthritis in weight-bearing joints.

In her lab at Boston University, Lewis has designed a device, called a robotic hip exoskeleton, that she hopes will help shrink the suffering by teaching people how to correct their walking styles.

There’s a lot that can go wrong in a single step.

“They may not be pushing with their foot as much as they should be,’’ Lewis said, “or they may be taking too long of a step, so their leg ends up far behind them.’’

Another walking no-no is excessive swinging of the pelvis from side to side.

“While that may be sexy, it may not be the best for their hip joints,’’ Lewis said.

The plastic and metal robotic device she designed, which is strapped around the pelvis and thighs, weighs about 11 pounds and is powered by an air compressor attached to each thigh - think bicycle pump - that is turned on by the researcher at the precise point when a person walking on a treadmill needs some correction. For instance, the compressor can exert pressure on the front of the thigh to shorten a stride.

Lewis’s earlier research indicates that the device can help people change the way they walk while they are wearing it. But the researchers still have several more years of work to know whether the changes will be lasting, and whether such retraining might head off hip problems.

Across the Charles River, at the Spaulding National Running Center in Cambridge, director Irene Davis has focused on knee, rather than hip, osteoarthritis.

Davis has been studying runners and their injuries for 25 years, and more recently has become an advocate of barefoot running, as well as minimal support in other types of footwear.

She said the layers of cushioning typically found in shoes can alter a person’s running style and can contribute to injuries.

“The cushioning has encouraged heavier landing on your heel, and that puts an impact on your body that was not meant to be there,’’ said Davis, who is a physical therapist with a doctorate in biomechanics.

Researchers are finding that certain injuries, for instance the growing number of anterior cruciate ligament, or ACL, knee injuries, in high school and college sports can significantly increase the likelihood that athletes will develop severe knee osteoarthritis 10 to 20 years later.

Scientists are also finding that chronic stress on the knees from an abnormal walking style, as is the case with people who are bowlegged, can increase their chances of developing arthritis in those joints.

Davis has studied bowlegged walkers and has found that placing a wedge-shaped orthotic in their shoes that is thicker on the outside can coax their knees inward toward a more normal position, but still not in the normal range.

Much more effective was a different approach by Davis that placed bowlegged walkers on a treadmill with a real-time graphic of their gait in front of them. The interactive graphic showed their exact knee position with each step, along with a shaded “normal’’ region that they were instructed to aim for.

“With each foot strike, they learn to pull their knee in a bit more,’’ Davis said.

She reported her findings in a study published last year in the Journal of Biomechanics. The study found that the bowlegged walkers learned to walk differently after eight sessions, and were able to demonstrate the corrected walking style a month later.

But these otherwise healthy walkers confessed that they didn’t typically walk with that corrected gait in the interim month outside Davis’s lab. They didn’t feel pain when walking in their usual bowlegged style - even though it may be wearing down their knee joints - so they had no incentive to stick with the corrected gait, Davis said.

Now she is planning on developing a device, perhaps something small that could be slipped into a shoe, that would give the bowlegged walkers a gentle reminder, “so that when they drift back, they get a little buzzing sound,’’ Davis said.

She is also planning another gait retraining study on bowlegged individuals who already have painful knee osteoarthritis.

Researchers working on gait retraining are typically studying people younger than 50 because they are more agile and able to make changes.

As scientists better understand joint deterioration and osteoarthritis, they are realizing the disease often begins much earlier than they previously realized.

“We have thought about the disease in the wrong way,’’ said Dr. John Hardin, chief science officer for the Arthritis Foundation.

Just as scientists have come to understand that cardiovascular disease doesn’t start with a heart attack, but years earlier when arteries are beginning to get clogged, they are now realizing that cartilage in joints begins to break down within days of certain injuries, such as an ACL tear in the knee, Hardin said.

The foundation, along with the National Institutes of Health, is funding a study that is searching for a marker that could pinpoint in a patient’s blood, urine, or by X-ray, the earliest signs of trouble, long before someone feels arthritis pain.

The ultimate goal is to be able to routinely test a patient for that marker, so that someone who has an ACL knee injury, for instance, could be offered a treatment that would halt the cartilage breakdown at the earliest stages, Hardin said.

But it will likely be 10 to 15 years before such treatments are on the market, he said.

Which is why the foundation is pushing programs now to help children and teens build strong cartilage through physical activity.

“There are studies that show if you exercise high school students their cartilage gets stronger,’’ Hardin said. “The time to start thinking about preventing osteoarthritis is in childhood.’’

Kay Lazar can be reached at Follow her on Twitter @GlobeKayLazar.

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