According to a study, middle-aged men and women who engage in high levels of physical activity could be causing damage to their knees and increasing their risk for osteoarthritis. The study results also indicated that some activities carry a greater risk of knee damage over time.

Osteoarthritis is a degenerative joint disease that causes pain, swelling and stiffness. Osteoarthritis is the most common form of arthritis and affects an estimated 27 million American adults. Osteoarthritis mostly affects cartilage, the hard but slippery tissue that covers the ends of bones where they meet to form a joint. Healthy cartilage allows bones to glide over one another. It also absorbs energy from the shock of physical movement. In osteoarthritis, the surface layer of cartilage breaks down and wears away.  Osteoarthritis sufferers usually have joint pain and some movement limitations. Unlike some other forms of arthritis, such as rheumatoid arthritis, osteoarthritis affects only joint function and does not affect skin tissue, the lungs, the eyes, or the blood vessels.

Image: Top: A magnetic resonance (MR) image showing the right knee of a patient with moderate physical activity. Bottom: MR image showing the right knee of a patient with high physical activity, high PASE Scale score and area of full thickness loss of the medial femur cartilage.

"Our data suggest that people with higher physical activity levels may be at greater risk for developing knee abnormalities and, thus, at higher risk for developing osteoarthritis," said study author Christoph Stehling.

The study involved 236 asymptomatic participants who had not reported previous knee pain and were enrolled in the National Institutes of Health Osteoarthritis Initiative. Study participants included 136 women and 100 men, age 45 to 55, within a healthy weight range. The participants were separated into low-, middle-, and high-activity groups based on their responses to the Physical Activity Scale for the Elderly (PASE) questionnaire. PASE is a standard test that scores an older individual's physical activity level, based on the type of activity and the time spent doing it. Several factors contribute to the final PASE score, but a person whose activity level is classified as high typically might engage in several hours of walking, sports or other types of exercise per week, as well as yard work and other household chores.

Subsequent MRI analysis by two musculoskeletal radiologists indicated a relationship between physical activity levels and frequency and severity of knee damage. Specific knee abnormalities identified included meniscal lesions, cartilage lesions, bone marrow edema and ligament lesions. Abnormalities were associated solely with activity levels and were not age or gender specific.

"The prevalence of the knee abnormalities increased with the level of physical activity," Dr. Stehling said. "In addition, cartilage defects diagnosed in active people were more severe."

"This study and previous studies by our group suggest that high-impact, weight-bearing physical activity, such as running and jumping, may be worse for cartilage health," Dr. Stehling said. "Conversely, low-impact activities, such as swimming and cycling, may protect diseased cartilage and prevent healthy cartilage from developing disease."
References:
1. Christoph Stehling, et al. Subjects with Higher Physical Activity Levels Have More Severe Focal Knee Lesions Diagnosed with 3T MRI: Analysis of the Non Symptomatic Incidence Cohort of the Osteoarthritis Initiative. Radiological Society of North America, November 30 2009.
2. The National Institute of Arthritis and Musculoskeletal and Skin Diseases.