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The knee is the most common joint affected by osteoarthritis or degenerative joint disease, a major cause of disability in the United States, researchers say. In the United States, nearly 27 million adults suffer from osteoarthritis, and 16% of cases in people aged 45 and older affect the knee. Almost 19% of symptomatic knee osteoarthritis patients are women and 13.5% are men, according to the U.S. Centers for Disease Control and Prevention.
However, the new study finds that "stronger quadricep [thigh] muscles may protect older adults from developing the combination of osteoarthritis on X-ray and daily pain or stiffness in their knees," said lead researcher Dr. Neil Segal, director of the Clinical Osteoarthritis Research Program at the University of Iowa.
"We already knew that quadriceps strength was associated with better ability to walk and get up from a chair," Segal said. "However, one implication of these new findings is that quadricep strength may protect against developing symptomatic knee osteoarthritis."
The report is published in the September issue of Arthritis Care & Research.
For the study, Segal's team followed more than 3,000 men and women between 50 and 79 years of age, all of whom took part in the in the Multicenter Knee Osteoarthritis Study (MOST). The trial was designed to find out if knee strength would predict knee osteoarthritis, either as observed on an X-ray or through patient symptoms.
Over two and a half years, the researchers evaluated each participant for thigh muscle strength. Muscle strength between the quadriceps and the hamstrings was used to determine weakness in the lower leg muscles. To see if people developed osteoarthritis, the researchers took X-rays of the participants' knees at the beginning and end of the study. They also asked about pain, aching or stiffness in the knees.
By the end of the study, 48 of 680 men and 93 of 937 women developed osteoarthritis detectable by X-ray. About 10% of the women and 8% of the men had symptoms of knee osteoarthritis, the researchers found.
These results showed that thigh muscle strength was not a significant predictor of osteoarthritis that was detected via X-ray. However, women with the strongest thighs had a lower incidence of symptomatic, or painful, knee osteoarthritis, Segal's group found.
However, men with strong thigh muscles had only slightly better odds of avoiding painful knee osteoarthritis compared with men with weaker knee extensor strength.
It remains to be seen whether strengthening the thighs might help people avoid arthritic knees, the researchers stressed. "Our study was observational, so interventional studies need to be done to determine whether strengthening exercises for people with weak quadriceps will reduce their risk for developing symptomatic knee osteoarthritis years later," Segal said.
Samantha Heller, an exercise physiologist, said a few simple, low-impact exercises can help people -- even those with osteoarthritis -- strengthen their thighs and knees.
"The exercises that people can do, and tend to do correctly, and can do on their own, are climbing stairs -- up and down," Heller said.
Heller recommends climbing stairs slowly, making the best use of the thigh muscles. "You don't have to run up or down stairs. You can go up and down even one or two steps at a time -- that helps strengthen the leg muscles. Strong leg muscles not only support knee health, but they support your independence as you get older," she said.
In addition, walking is good for your muscles and your bones, Heller said. Walking engages all the muscles in your legs, she added. "If you want to have happy knees, you want to have the muscles surrounding the knee strong and balanced," she said.
People can also see a physical therapist to get on a program that will strengthen the legs, Heller said. "There's a whole ton of leg and knee exercises you can do," she said.
SOURCES: Neil Segal, M.D., associate professor and director, Clinical Osteoarthritis Research Program, University of Iowa, Iowa City; Samantha Heller, R.D., C.D.N., registered dietitian, clinical nutritionist, exercise physiologist, Fairfield, Conn.; September 2009 Arthritis Care & Research
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