CHICAGO (EGMN) –The wisdom about practicing everything in moderation also may hold true for knees, especially in middle-aged adults with risk factors for osteoarthritis.

Light exercise, such as walking, appears to protect against OA, but the extremes – a sedentary lifestyle or more aggressive workouts – may accelerate OA onset in at-risk individuals, according to baseline data from the Osteoarthritis Initiative, a longitudinal, multicenter, observational study funded by the U.S. National Institutes of Health.

Osteoarthritis risk can be reduced by avoiding aggressive exercise and exercising safely, said the study’s lead author, Dr. Thomas M. Link, professor of radiology and chief of musculoskeletal imaging at the University of California, San Francisco.

Among at-risk patients, light exercisers had significantly less degeneration of the cartilage surrounding the knees on magnetic resonance imaging (MRI) than did those whose exercise routines were characterized as either minimal or moderate to strenuous.

Middle-age adults, particularly those with OA risk factors, need to be “extremely careful” with their cartilage, Dr. Link said in a press briefing Nov. 29 during the annual meeting of the Radiological Society of North America. “Once cartilage is gone, it’s gone forever.”

This doesn’t mean that patients should stop running or playing tennis, but it does mean they must make sure they are exercising safely to avoid sustaining an injury that could “initiate an osteoarthritis cascade, which will be very difficult to stop,” he said.

Research associate Keegan K. Hovis, R.N., said the key for patients who exercise strenuously is to focus on modifiable risk factors, such as maintaining a healthy weight and strengthening the knee stabilizing muscles, including the quadriceps.

Subjects included 132 at-risk patients and 33 controls matched for age and body mass index (99 women and 66 men between the ages of 45 and 55 years, BMI range of 18-27 kg/m²). Risk factors for OA included a previous knee injury or knee surgery, a family history of total knee replacement surgery, bone spurs on the fingers, and occasional knee symptoms.

Based on responses to the leisure activity component of the Physical Activity Scale for the Elderly, study participants were stratified according to intensity of exercise habits into sedentary, light, or moderate-strenuous exercisers. Patients also were grouped by whether they engaged in frequent knee-bending activities. These activities included climbing at least 10 flights of stairs daily, lifting objects weighing more than 25 pounds, or squatting, kneeling, or deep-knee-bending for at least 30 minutes per day.

Sedentary exercisers walked less than or equal to 2 days a week for less than 2 hours per day. Light exercisers walked or participated in other forms of light exercise such as table tennis or Frisbee plastic disk at least 3 days a week for less than 2 hours a day. Moderate-strenuous exercisers engaged in sports such as running, tennis, or soccer at least 3 days a week for greater than or equal to 1 hour per day.

To assess cartilage health, researchers used T2 mapping, a quantitative and qualitative MRI technique that, unlike anatomic imaging, reveals the chemical composition and structure of the cartilage (including collagen and water content) and can provide an image marker of cartilage degeneration in its earliest stages.

“T2 values can detect changes in cartilage at the molecular level, prior to irreversible changes in the structure; therefore, it has the potential to identify, with the earliest signs of degeneration, who may benefit from early treatment or behavioral intervention,” said Dr. Link.

Two radiologists analyzed T2 values in five cartilage areas – patella, medial femur, medial tibia, lateral femur, and lateral tibia – and graded overall visible signs of cartilage and meniscus damage using a modified whole-organ MRI scoring method (WORMS).

Among the 132 at-risk patients, T2 values were significantly lower, indicating less cartilage degeneration, in light exercisers than sedentary and moderate-strenuous exercisers in the overall average of all compartments (43.5 vs. 44.5 and 45.0, respectively) and in the lateral tibia (38.0 vs. 39.7 and 40.2). “Light exercise was associated with more intact collagen structure and lower cartilage water content, which are indicative of healthier cartilage,” said Ms. Hovis.

Moderate-strenuous exercise in women was significantly correlated with higher T2 values in the medial femur, indicating that moderate-strenuous exercise may accelerate cartilage degeneration and increase osteoarthritis risk in women who engage in more intense workouts, she reported.

Differences in cartilage health were not found in any of the three exercise groups in the control cohort. However, knee-bending activities were associated with higher T2 values in both the at-risk and control cohorts. In the at-risk cohort, those who engaged in frequent knee-bending activities had significantly higher T2 values in all compartments than those who did not (44.7 vs. 43.2) and a significantly higher WORMS score, indicating visible signs of cartilage degeneration. In the normal cohort, knee-bending activities were associated with higher T2 values in the medial femur and the medial tibia (49.9 vs. 47.0 and 35.4 vs. 32.5, respectively) with a trend toward significance in the overall average in all compartments.

“Knee-bending activity may accelerate cartilage degeneration in all individuals, but potentially to a greater degree in subjects already at risk for knee osteoarthritis,” Ms. Hovis said.

The researchers plan to collect longitudinal data at 2 and 4 years and are finishing an analysis of data on strength training.

Dr. Link disclosed that he has received research support from Merck & Co. Inc.

Copyright (c) 2010 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

芝加哥 (EGMN)——一项多中心纵向观察研究(Osteoarthritis Initiative)的基线数据显示，步行等轻度运动可预防骨关节炎，但久坐或过度运动可加速高危人群骨关节炎的发生。

该研究由加利福尼亚大学放射学教授Thomas M. Link博士带领完成，共纳入132例有骨关节炎危险因素的患者以及年龄和体重指数与之相匹配的33名对照者(女性99名，男性66名，年龄45~55岁，体重指数18~27 kg/m²)。骨关节炎的危险因素包括既往膝关节创伤或膝关节手术、全膝关节置换术家族史、手指骨疣以及偶尔出现膝关节症状。根据老年人身体活动量表将受试者按照活动强度习惯分为久坐者、轻度或中重度活动者。另外，根据是否经常屈膝将患者分组，屈膝活动包括每天至少爬十个台阶、举起25磅以上的物体，或蹲着、跪下或深度屈膝每天至少30min；久坐者每周步行不超过2天，每天少于2h；轻度活动者步行或参加其他形式的锻炼，如乒乓球或飞盘，每周至少3天，每天少于2h；中重度活动者参加的体育活动如跑步、网球或足球，每周至少3天，每天不少于1h。

研究者采用T2 mapping成像评价软骨的健康状况，这是一种定量和定性的MRI技术，可显示组织成分和软骨结构（包括胶原和水含量），可早期诊断膝关节软骨损伤。两名放射学家分析膝关节髌骨、股骨内侧髁、胫骨内侧髁、股骨外侧髁、胫骨外侧髁5处软骨的T2值，采用修订的全器官MRI评分方法(WORMS)对可见的软骨征象和半月板损伤分级。

结果显示，在132名高危患者中，同久坐者和中重度运动者相比，轻度运动者所有部位的平均值（分别为44.5、45.0和43.5）和胫骨外侧髁的T2值(分别为39.7、40.2和38.0)显著降低，提示软骨退化较少。轻度运动与软骨结构完整和软骨水含量少相关，说明软骨更健康。

在女性，中重度运动与股骨内侧髁T2值较高相关，提示中重度运动加速软骨退化，在从事更剧烈活动的女性可增加骨关节炎发病风险。

在对照组，三种运动方式对软骨健康状况的影响没有差别。然而，在高危组和对照组，屈膝活动与T2值升高有关。在高危组，经常屈膝活动者所有5个部位的T2值显著高于其他人(44.7 vs. 43.2)，WORMS评分显著升高。在正常对照组，屈膝活动与股骨内侧髁和胫骨内侧髁的T2值升高有关(分别为49.9、47.0，和35.4、32.5)。在所有受试者，屈膝活动可加速软骨退化，有膝关节骨关节炎风险的受试者软骨退化程度更重些。

三色T2加权磁共振成像扫描序列的第一回波显示：(A)久坐者胫骨外侧髁T2值高；(B) 轻度运动者胫骨外侧髁T2值低；(C) 有骨关节炎危险因素的中重度运动者胫骨外侧髁T2值高。 (RSNA提供，已获准使用)

该研究由美国国立卫生研究院资助。Link博士披露其接受了默克公司的科研支持。

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