Knee osteoarthritis (OA) is being diagnosed at a much younger age than it was about 20 years ago – and it’s expected to place an additional burden on the health care system in the United States, according to a study presented at a meeting of the American College of Rheumatology in Chicago. The good news, according to a second study presented at the conference, is that that weight loss in combination with exercise can reduce pain and improve function in people with knee OA.

Elena Losina, PhD, co-director of the Orthopaedic and Arthritis Center for Outcomes Research at Brigham and Women’s Hospital in Boston, who presented the first study, suggests that the increased incidence of knee OA in younger adults may be partly related to what the Centers for Disease Control and Prevention has called the national obesity epidemic and to an increasing number of knee injuries.

The study shows that knee OA is diagnosed about 13 years earlier than it was in the 1990s, and the earlier age at diagnosis has led to a dramatic increase in total knee replacement surgeries in people younger than age 65. If the trend continues, it is estimated that more than half of all new diagnoses of knee OA will be in people ages 45 to 64.

“The mean age of onset of physician-diagnosed OA fell from 69 years in the 1990s to 56 years in 2010, according to our study,” says Losina. “Our findings are consistent with the recently observed tripling of total knee replacement use in 45- to 65-year-olds in the U.S. Now about 40 percent of all knee replacements are done in people under age 65.”

But not all of these patients may need surgery. A separate study presented at the conference found that weight loss along with exercise reduces pain and improves symptoms in people with knee OA. The Intensive Diet and Exercise for Arthritis trial evaluated the impact of weight loss and exercise in reducing pain associated with knee OA, and in improving function and mobility in 454 overweight adults with symptomatic knee pain. The diet-alone and the diet-plus-exercise groups were compared to a control group that exercised but did not attempt to lose weight. Exercise consisted of one hour of low to moderate intensity walking and resistance training three days a week.

After 18 months, among the 399 adults who completed the study, the group who dieted and exercised lost 11.4 percent of their body weight, the group that just dieted lost 9.5 percent of body weight, and the exercise-only group lost 2.2 percent of their body weight. The diet-plus-exercise group also had the best outcomes for reduced pain – by about 50 percent – and for improved function and mobility.

“Clinicians can tell their patients that they will see marked improvement in pain and function in six months or less with intensive diet and exercise, but significant differences favoring intensive diet and exercise may take as long as 18 months to appear,” says lead author Stephen P. Messier, PhD, professor and director of the J.B. Snow Biomechanics Laboratory and Wake Forest University Runners’ Clinic at Wake Forest University in Winston-Salem, N.C.

A third study presented at the conference may relieve worries that exercise and sports will lead to knee OA.

“Most sports probably don’t increase the risk of knee OA, especially if participation is recreational. People who want to reduce their risk of knee OA should participate in non-contact and low-impact sports, such as doubles tennis, swimming and cycling,” says lead author Jeffrey B. Driban, PhD, research associate at Tufts Medical Center in Boston.

Driban and colleagues looked at 16 studies with a total of 3,192 participants and found that knee OA occurred in 8.4 percent of former sports participants compared with 9.1 percent of people who did not participate in sports, suggesting that sports activity does not generally increase the risk of knee OA. However, the risk was higher in soccer players as well as elite long-distance runners, weight lifters and wrestlers – sports that involve weight bearing on the knee.

Scott J. Zashin, MD, clinical professor of medicine at the University of Texas Southwestern Medical School in Dallas, cites several possible reasons for the increase in knee OA among younger people: increased awareness by physicians as well as by patients seeking help for their symptoms; obesity; and more children playing soccer at younger ages and playing it year-round.

“I tell my patients that every 1 pound of body weight is equivalent to 4 pounds of weight on your knee,” Dr. Zashin says. “One of the best treatments that doesn’t involve medications is maintaining one’s ideal body weight.”