An estimated 10 million Americans suffer from knee arthritis. New projections indicate 6.5 million Americans between the age of 35 and 84 will be diagnosed with it in this decade.

“The diagnosis of knee osteoarthritis is occurring much earlier,” said Elena Losina, Ph.D., author of the study and co-director of the Orthopedics and Arthritis Center at Brigham and Women’s Hospital in Boston.

In the 1990s, the average age at diagnosis was 69. In the last decade, it was 56, she said.

Dr. Losina suspects that a rise in obesity and knee injuries in the 2000s may be spurring on the increase in knee arthritis.

Knee injuries – and certain sports -- have been linked to an increased risk of knee arthritis, said another researcher, Dr. Jeffrey Driban, an assistant professor of rheumatology at Tufts Medical Center in Boston.
Soccer players, long-distance runners, competitive weight lifters and wrestlers showed a higher risk of knee injuries and arthritis in studies, he said. Sports with a lower knee injury risk include cycling and swimming.

Losing weight if overweight may help those who have knee arthritis, experts suggest.