A study following more than a thousand medical school graduates for nearly 40 years has shown that young adults who've injured their knees have a substantially increased risk of developing arthritis as older adults.

A Hopkins research team, reporting in the Sept. 5 issue of the Annals of Internal Medicine, offers strong evidence that early trauma to the knees is a trigger for osteo-arthritis, the leading type of arthritis in the United States. The study also suggests that physicians may need to shift their approach to the disease, to one of prevention. "When you ask how early to intervene to prevent osteoarthritis," says rheumatologist Allan C. Gelber, who led the research team, "this study tells us 'the sooner the better.' "

Study participants who had suffered knee injuries as teens or young adults had a nearly threefold increase in risk of osteoarthritis by age 65, Gelber says.

The study also showed that those who'd had joint injuries as adults had an increased risk of osteoarthritis later on--fivefold for knees and threefold for hip injuries.

"While the results of our research may surprise no one--most people intuitively believe you're more prone to arthritis if you've had a joint injury some time in life--this proof has been fairly slow in coming," Gelber says.

"Until now, most studies have been cross-sectional: They compare groups of older people with arthritis and those without and ask, 'Have you ever had an injury?' But there are limits to the accuracy of that approach," Gelber explains. "People who are physically impaired or in pain often don't recall prior injuries accurately."

The present study is unusual, he says, because it's large and has permitted researchers to record both the injury--at a time close to when it occurred--and the development of the disease.

The researchers also followed participants with hip injuries, both early on and later in life. Having a hip injury later in life apparently made people more prone to arthritis than did earlier injury, though the results of that part of the study are less strong, says Gelber, because relatively few study members had injured their hips.

The research considered 1,321 subjects from the Johns Hopkins Precursors Study, a project begun in 1948 to spot early signposts for disease. From 1948 until 1964, the Precursors Study recruited graduates of the Hopkins School of Medicine--mostly white men in their 20s--and followed them through the years. Participants initially filled out a detailed health questionnaire and took a standard physical exam, which noted previous trauma to knee or hip joints. Then the researchers surveyed participants' health with annual questionnaires. This present study followed them through November 1995, a period of about 36 years for most, when they'd reached their early 60s.

Of the 47 people with early knee injuries--about 4 percent of those studied--most had had fractures or direct damage to joint cartilage or ligaments, Gelber says. At the end of the research period, many of them had symptoms of osteoarthritis such as joint tenderness and pain. Half were taking drugs for the problem, and a significant number had needed surgery, including joint replacement or arthroscopic surgery.

"This suggests that we should probably intervene before people develop arthritis, before symptoms appear," Gelber says. "Because many of the injuries were sports-related," he says, "perhaps we could make the sports young adults play safer--with safer equipment or on safer surfaces. Or we could also intervene after the injury, perhaps making greater use of braces or giving up a certain activity altogether. Finally, we need to develop new therapies for osteoarthritis, ones that go beyond pain relief to reconstitute damaged cartilage."

Osteoarthritis affects an estimated 21 million people in the United States.

Other researchers in the study were Nae-Yuh Wang, Fredrick Wigley, Lucy Mead and Michael Klag, of Johns Hopkins; and Marc Hochberg, from the University of Maryland, Baltimore.

Funding for the study was through grants from the National Institutes of Health and the Arthritis Foundation.