Reuters -- As Americans put their surfboards into storage, they're taking their ski and football gear out of mothballs. But a new report might make you think twice before hitting the slopes or the gridiron this season--US researchers say that a knee injury increases the risk of osteoarthritis in the joint later in life by as much as 3 to 5 times.
The study, based on data collected from over 1,300 people who graduated from Johns Hopkins Medical School between 1948 and 1964, showed that those who injured their knee during their teens or twenties had a three times higher risk of developing arthritis in the joint later in life than those who did not sustain knee injuries at those ages. In addition, the researchers found that those who injured a knee or hip later in adulthood had a five times greater risk of knee osteoarthritis and a three times greater risk of developing arthritis in the hip.
Dr. Allan C. Gelber, a rheumatologist who led the research team, noted that the study backs up previous research that linked joint injury to arthritis risk. Gelber said the new study differs from previous ones in the way it was conducted--instead of asking older people with arthritis if they were injured, it tracked a group of people over 36 years, using questionnaires to determine if they had injured a joint and/or developed arthritis. This prospective type of study design is thought to give more accurate results than the retrospective one.
"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," said Gelber in a statement.
In their report, published Tuesday in the Annals of Internal Medicine, the researchers note that previous injury was a risk factor for knee osteoarthritis, even after factors such as higher levels of physical activity in young adulthood and heavier body weight in later adulthood were taken into account.
"Harmful forces inflicted on a joint during injury lead to cartilage breakdown, (bone) microfracture, and bone remodeling," setting the stage for later arthritis, Gelber's team explains. Muscles may also be affected by joint injury, they add, either directly at the time of injury or indirectly due to disuse during convalescence. Weakness of the quadriceps muscles, at the front of the thigh, is related to later development of knee osteoarthritis.
The team acknowledges that their study has limitations--the study participants were 91% male and 97% white, and all were physicians. Thus the results may not apply to women, other races, or people in other occupations. Also, the researchers relied on the participants' answers on questionnaires, asking them about osteoarthritis symptoms, rather than examining them regularly or checking their medical records. However, the researchers did look at x-rays to confirm osteoarthritis in those reporting symptoms.
The study authors conclude that their findings "strongly demonstrate" that knee injuries during adulthood increase the risk of developing osteoarthritis at the same joint later in life.
"This suggests that we should probably intervene before people develop arthritis, before symptoms appear," said Gelber. "Because many of the injuries were sports-related, 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 on a certain activity altogether."
"Finally, we need to develop new therapies for osteoarthritis, ones that go beyond pain relief to reconstitute damaged cartilage," he added.
Health experts estimate that 21 million Americans have osteoarthritis.
SOURCE: Annals of Internal Medicine 2000:133:321-328.
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