膝关节的骨性关节炎（knee osteoarthritis）正日益威胁着美国的年轻一代，与上世纪90年代比较，如今美国人被诊断为膝关节骨性关节炎者的平均年龄已由当年的69岁降低至56岁，提示患膝关节的骨性关节炎者越来越年轻。另有推测认为“在接下来的十年间将有6500万年龄在35～84岁间的美国人被诊断为膝关节的骨性关节炎”。为何膝关节的骨性关节炎如此常见？显然与人寿的延长、不当的运动方式（如频繁的登楼梯、登山和跑步或反复下蹲、踢足球、举重和摔跤等）及超重或肥胖的体格等有关。最近，有学者报告“采用饮食治疗＋运动疗法以降低膝关节骨性关节炎之患者的体重，可以减轻这类患者的膝关节疼痛及增加其膝关节的运动能力，如行走更自如、更远和膝关节活动度更大等。由此可见，维持一个健康的体重对保护或改善膝关节的功能具有相当重要的意义。

Knee Arthritis Striking at Younger Ages, But Weight Loss May Help

Studies suggest playing sports longer, extra pounds might explain trend

SATURDAY, Nov. 5 (HealthDay News) -- Arthritis of the knee is striking Americans at younger ages, new research has found, but shedding a few pounds if you're overweight may reduce your risk.

The studies were to be presented Saturday at the American College of Rheumatology annual meeting, in Chicago.

Nearly 6.5 million Americans between the ages of 35 and 84 will receive a diagnosis of knee osteoarthritis in the next decade, according to these new projections.

"The diagnosis of knee osteoarthritis is occurring much earlier," said study author Dr. Elena Losina, co-director of the Orthopedics and Arthritis Center for Outcomes Research at Brigham and Women's Hospital in Boston.

When she compared the age at diagnosis in the 1990s to ages in the 2010s, "the average age at diagnosis has moved from 69 to 56," she said.

It strikes some earlier than the average age, of course. Losina found that adults aged 45 to 54 will account for nearly 5 percent of all knee osteoarthritis (OA) cases in the 2010s, while they represented only 1.5 percent of the knee OA patients in the 1990s.

Losina suspects that obesity and knee injuries, both of which have become more common in the past decade, may be helping to drive the increase in knee OA among younger people.

Injuries to the knee have been linked with an increased risk of knee arthritis. And certain sports are riskier than others, said another researcher, Dr. Jeffrey Driban, an assistant professor of rheumatology at Tufts Medical Center in Boston. He reviewed studies that looked at a link between sports participation and knee OA. He focused on 16 studies, and then honed in on 10 that looked at athletes and nonathletes.

While there were not great differences later in the amount of knee OA for former sports players and nonathletes, he did find a risk linked with the type of sport and level of participation.

Soccer players, whether elite level or not, had a greater risk of knee OA, he found. So did elite long-distance runners, competitive weight lifters and wrestlers.

The increased risk of arthritis in these participants varied from about threefold to more than sixfold compared to nonathletes, he said.

For those who already have knee OA, the best medicine may be weight loss if they are overweight, and exercise.

In another study, Dr. Stephen Messier of Wake Forest University found that a program of diet and exercise reduced pain and improved mobility by as much as 50 percent in those with knee arthritis.

He assigned adults with knee OA and pain to one of three groups for the 18-month program. One group dieted only, one group exercised only and one group did both.

In all, 399 overweight or obese men and women, average age 66, completed the study. The diet and exercise group lost the most weight, averaging 11.4 percent of their body weight. The diet-only group lost 9.5 percent; the exercise-only group lost 2.2 percent.

When they compared pain and mobility, the diet and exercise group reported much less pain and had greater walking speed than the other groups.

Driban suggested that those who want to minimize the risk of knee OA later should consider sports with a lower knee injury risk, such as swimming and cycling.

However, a sports medicine specialist took issue with that suggestion. "There is no evidence that impact sports like running causes arthritis in a healthy knee," said Dr. Stephen Nicholas, director of the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital, in New York City.

Like other experts, he does agree that once a knee injury occurs, a person is at higher risk for knee arthritis.

However, if someone has a healthy knee, Nicholas said he would tell them to pick the sport they enjoy.

Losina's research was funded by the U.S. National Institutes of Health's National Institute of Arthritis and Musculoskeletal and Skin Diseases. All three studies should be viewed as preliminary, as they were presented at a medical meeting and not yet peer-reviewed.

SOURCES: Stephen Nicholas, M.D., director, Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York City; Jeffrey B. Driban, Ph.D., assistant professor, rheumatology, Tufts Medical Center, Boston; Elena Losina, Ph.D., co-director, Orthopedics and Arthritis Center for Outcomes Research, Brigham and Women's Hospital, Boston; Nov. 5, 2011, presentation, American College of Rheumatology, annual meeting, Chicago