Knee Osteoarthritis - New Study Shows Higher Risk

A large, population-based study in N.C. finds the lifetime risk of knee OA is greater than the lifetime risk of diabetes.

By Brenda Goodman

9/15/08 Researchers tracking knee pain in the population of a North Carolina county say the knee osteoarthritis risk is far higher than experts had known. The results of their latest study suggest that nearly 1 in 2 people will develop osteoarthritis in a knee before they reach the age of 85, with the risk approaching 2 in 3 for people who are overweight or obese.

By comparison, 1 in 8 women will get breast cancer in her lifetime and 1 in 3 men and 2 in 5 women will get diabetes in their lifetimes – making osteoarthritis of the knee more common than either of those ailments. (Read Arthritis Today's exclusive interview with the study's authors.) 

“This indicates a higher risk of arthritis than has been appreciated before,” said John Hardin, M.D., a rheumatologist and Chief Scientific Officer of the Arthritis Foundation, a national volunteer health organization based in Atlanta. The study was published in the Sept. 15, 2008 issue of Arthritis Care & Research.

“This is a very important knee osteoarthritis study. It is very well done, and I think it’s going to be one of the cornerstones of our discussions of arthritis in the future,” Dr. Hardin said. 

For this analysis, a team of investigators from the Centers for Disease Control and Prevention in Atlanta and the University of North Carolina at Chapel Hill followed more than 3,000 people living in six townships of Johnston County, N.C., for almost two decades. (Read about how the study was conducted and who the participants are.) 

The knee osteoarthritis study participants were asked to answer a battery of interview questions and given a slew of medical tests, including X-rays of their hips, knees, spine and hands. Five to seven years later, they were asked to repeat the process. (Learn more about the study participants.) 

After examining the baseline and follow-up data, researchers estimated that the risk of having symptoms of osteoarthritis in at least one knee by age 85 was 45.5 percent. Race, sex and education level seemed to have no effect on the risk of getting arthritis in a knee. 

But risk escalated significantly with increasing body weight. Those who maintained a normal weight over the course of their lives had the lowest lifetime risk of any group in the study – 30 percent. Those who were normal weight at age 18, but overweight or obese at the start of the study (27 or more years prior) and at their follow-up exams, had the highest lifetime risk of knee osteoarthritis – 60 percent.

“We hear a lot about why the obesity epidemic is so important,” said Joanne Jordan, MD, PhD, professor of medicine and orthopedics at the University of North Carolina at Chapel Hill. “We hear that you need to lose weight to prevent diabetes or lose weight to prevent heart disease. We never hear that you need to lose weight to prevent arthritis. But it is critical to realize that if you gain weight, you’re going to get arthritis in your knees and you’re going to be miserable.”

Previous studies have shown that being just 10 pounds overweight increases the force on the knee by 30 to 60 pounds. In another study of osteoarthritis in a population in Framingham, Mass., researchers estimated that a woman who lost 11 pounds or about 2 Body Mass Index (BMI) points, decreased her risk of osteoarthritis by more than 50 percent. Calculate your BMI.

Injuries also elevated knee osteoarthritis risk; 58 percent of those with a history of knee damage could expect to develop arthritis later in life.

“The key to preventing disease is preventing the injury to begin with,” Dr. Hardin said.  “Once the damage is done and the cartilage has been injured, it’s very hard to think about how you might recover from that,” he added.

Dr. Hardin said keys to preventing osteoarthritis include maintaining proper weight and preventing injury. And doing one helps with the other. Keeping muscles strong, particularly the quadriceps, the big muscles on the front of the thighs, helps prevent knee injuries.

Arthritis is a major cause of disability in the United States. There are more than 100 types of arthritis and related conditions, and the most common kind is osteoarthritis.

Data collected by the Healthcare Cost and Utilization Project, a government survey, show osteoarthritis accounted for $10.5 billion in hospital charges in 2006, making it a more expensive condition than pneumonia, stroke, or complications from diabetes. In fact hospital admission for arthritis more than doubled from 1993 to 2006.

Knees, hips and fingers are the joints where osteoarthritis is most commonly diagnosed. Early symptoms of knee osteoarthritis include pain, stiffness in the joint in the morning that lasts more than 30 minutes, instability or buckling, a grinding or cracking noise in the joint, and swelling or inflammation.

“People should seek the help of their physicians when symptoms first appear,” Dr. Hardin said. “It’s not something to write off because there are things that can be done.”