FRIDAY, Nov. 9 (HealthDay News) -- Sore, arthritic knees may do better with flip-flops and flexible walking shoes than with other types of footwear, new research suggests.

In fact, the closer to barefoot, the better for the knees, the study finds.

"The main finding of the study is that footwear not only affects your feet but can affect other joints at your lower extremity, in particular the amount of load your knees experience when you walk," said lead researcher Dr. Najia Shakoor, an assistant professor of internal medicine at Rush University Medical College in Chicago.

Her team was to present the findings Thursday at the American College of Rheumatology annual meeting in Boston.

Previous research by Shakoor and her team suggested that walking barefoot was associated with lower load on the knees compared to walking with normal walking shoes.

A team of researchers at Rush performed gait analysis on 13 men and three women with osteoarthritis of the knee as they walked barefoot and then with two stability shoes (Dansko clogs and Brooks Addiction shoes), flip-flops and flexible walking shoes (Puma H-Street).

Right now, experts typically recommend stability shoes as supportive, stable and comfortable walking shoes.

A standard measure of load on the knee, using percent body weight times height, was assessed at normal walking speed.

The researchers found that the stability shoes were associated with significantly increased load on the knees compared to barefoot walking. Flip-flops, flexible walking shoes and barefoot walking all put a similar load on the knees.

Shakoor cautioned, "We are not advocating flip-flops. Flip-flops can be associated with other foot problems such as plantar faciitis and are probably not appropriate footwear for older individuals because of their increased association with falls. Therefore, based on this preliminary data we would probably recommend walking shoes over flip-flops for clinical use."

Physical therapist Teresa Schuemann agreed that flip-flops should not top the prescription pad for people with osteoarthritis. Schuemann, a spokeswoman for the American Physical Therapy Association, stressed caution when interpreting these results.

"Depending on what the sole of the shoe is made of, it may or may not absorb shock," said Shuemann, who pointed out that these results may be due in part to stability shoes having a more firm sole and less shock absorption as a result. Yet, she said, a more flexible sole may not be the long-term answer to knee pain. "The question is what is the alignment of the shoe. If your foot falls to the inside of the arch, you're going to be hurting your knee because you are not bearing weight on it."

Schuemann advised people who have been told to wear stability shoes to talk to their doctor about these results before slipping into flip-flops. Stability shoes are usually prescribed to help align the leg from foot to hip and also may be necessary for other reasons, such as arches that are too high or too low.

"If you have osteoarthritis and perfectly aligned feet, the more flexible shoes are probably helpful," she said. But only a minority of people can claim perfect alignment and as people get older and arches fall, that adds more stress to the feet, said Schuemann. The average age of people in the study was 56 -- prime fallen arch years.

The research, according to Shakoor, "gives a better understanding of the biomechanics of the lower extremity."

This is only the first step for the researchers, who plan to evaluate the long-term effects of specific shoes on joint loads in a controlled clinical trial.

"I think [this research] is actually quite novel from the standpoint of understanding that stresses and strains on feet and knees and hips aren't all to be regarded the same way," said rheumatologist Eric Matteson, of the Mayo Clinic. "What's interesting is that we have this emphasis on proper shoe wear, but we need to consider that what we wear has an impact on other joints."

Matteson said there are still some questions that need to be answered.

"We need to do a little bit more work on this. The study was very small and there are a lot of ways that gait analysis can be performed, although they did a pretty sophisticated gait analysis," he explained. "They don't have a lot of different kinds of patients with different kinds of knee problems and they don't have a great diversity of shoewear relating it to different kinds of problems, but it does make me reflect on some of the advice that I have been giving."

According to Matteson, osteoarthritis of the knee is not the same for all people. Some people feel pain inside their knees, others feel it on the outside. He expressed interest in determining how footwear might relate with the different manifestations of knee pain. Osteoarthritis is a massive problem, said Matteson, affecting 20 million to 30 million Americans every year.

"Literally hundreds of thousands of knee replacement surgeries are due to osteoarthritis," he noted.

Knee osteoarthritis is caused by cartilage breakdown in the knee joint. Factors that increase the risk of knee osteoarthritis include being overweight, age, injury or stress to the joints, and family history.

In knee osteoarthritis, there is abundant evidence that patients with abnormally high loading knees (high amounts of stress on part or all of the knee joint) are at increased risk of both injury and disease progression, according to the American College of Rheumatology.

More information

For more on osteoarthritis, head to the Arthritis Foundation.

SOURCES: Eric Matteson, M.D., consultant rheumatologist, Mayo Clinic, Rochester, Minn.; Teresa Schuemann, PT, SCS, ATC, CSCS, spokeswoman, American Physical Therapy Association; Najia Shakoor, M.D., assistant professor, internal medicine, Section of Rheumatology, Rush Medical College, Chicago; Nov. 8, 2007, presentation, American College of Rheumatology annual meeting, Boston

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