Flat feet tied to knee pain in older adults: MedlinePlus

Flat feet tied to knee pain in older adults


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Monday, January 24, 2011 Reuters Health Information Logo

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By Amy Norton

NEW YORK (Reuters Health) - Older adults with "flat feet" may be more likely than those with higher arches to have chronic knee pain, a new study suggests.

Researchers say the findings raise the possibility that flat feet sometimes contribute to knee osteoarthritis -- the common "wear-and-tear" form of arthritis in which the cartilage cushioning the joint breaks down.

If that's the case, they say, it could open up new ways to lower some older adults' risk of the painful knee condition.

The study, of 1,900 adults in their 50s or older, found that those with the flattest feet were 31 percent more likely than other study participants to say they had knee pain on most days. And they were 43 percent more likely to show damage to the cartilage at the inside of the knee.

The findings, reported in the journal Arthritis Care & Research, don't prove that flat feet caused the knee problems.

"We don't know which came first," said lead author K. Douglas Gross, a clinical research associate at Boston University School of Medicine and assistant professor of physical therapy at the Massachusetts General Hospital Institute of Health Professions in Boston.

Studies that follow people over time, looking at whether those with flat feet are more likely to develop knee pain or cartilage damage, are still needed to be sure, Gross told Reuters Health.

There is reason to believe that flat feet could be the culprit, however.

In general, people with flat feet have a lowered arch at the inside of the foot, such that if they wet their feet and stood on a flat surface, they would leave a complete footprint.

"When your feet flatten, it can change your posture or the way you move," Gross explained. One consequence may be that, when a person puts weight on a flat foot, the lower leg rotates inward -- which over time could damage the cartilage at the inner knee.

In their study, Gross and his colleagues found that 22 percent of all participants reported chronic knee pain. But it was more common when the same-side foot was flat.

They measured "flatness" with participants standing on both feet, then scored each foot using a common "arch index." Individual feet were then matched with the qualities of the knee of the same leg.

Of the flattest 1,047 feet the team examined, 30 percent came with a painful knee. That compared with a rate of 21 percent for all other feet.

When the researchers accounted for several other factors in knee arthritis risk -- like age and body weight -- having a flat foot was linked to a 31 percent greater chance of having chronic knee pain.

A similar pattern was seen when it came to cartilage damage at the inside of the knee, detected using MRIs. Such knee damage was found with 29 percent of the flattest feet, versus 19 percent of other feet.

If further studies show that flat feet do precede knee problems, then it might be possible to reduce that risk by using shoe inserts to support the inner arch of the foot, according to Gross.

But it's too soon to advise the flat-footed to run out and buy arch supports, he said.

"There are still many things we need to know before we can recommend that people do that," Gross said. "We're just at the first step."

All babies and toddlers have flat feet, with the arch developing during childhood. But some people maintain a lifelong flattened arch -- usually what's called a "flexible" flat foot, which does form an arch when you stand on your toes.

It's not clear how often people might develop flat feet later in life, according to Gross -- though it's possible that the aging process or factors like weight gain could contribute.

Also unclear, Gross said, is just how common flat feet are among older adults. It depends on how studies specifically define flat feet, he noted.

One recent study of an ethnically diverse sample of Americans age 65 and up found that 19 percent had flat feet.

About nine million Americans, more than half of whom are older than 65, have knee osteoarthritis. A 2008 government study estimated that 46 percent of U.S. adults can expect to develop arthritis in at least one knee by the age of 85.

SOURCE: http://bit.ly/dOKjoy Arthritis Care & Research, online January 10, 2011.
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Flat feet tied to knee pain in older adults: MedlinePlus