Fran Lowry

November 29, 2012

CHICAGO — People who engage in excessive high-intensity physical activity and those who do very little physical activity might be damaging their knee cartilage, according to research presented here at the Radiological Society of North America 98th Scientific Assembly and Annual Meeting.

Dr. Thomas Link

The loss of cartilage is progressive and irreversible. "Once the cartilage is gone, it is gone for good and cannot be recovered," said senior author Thomas M. Link, MD, PhD, chief of musculoskeletal imaging in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco (UCSF).

"This is why it is so important for people to do physical activity in moderation and to use safe practices when they do sports such as running and playing tennis," Dr. Link told Medscape Medical News.

To study the effects of exercise on the development of osteoarthritis of the knee, Dr. Link and his group measured T2 relaxation time using magnetic resonance imaging, which can detect biochemical changes in cartilage before irreversible loss occurs.

"In damaged cartilage, the water mobility is increased, [which] results in increased T2 relaxation time," Dr. Link explained.

A previous cross-sectional study demonstrated an association between a higher level of physical activity and higher T2 values at the patella, and between a moderate level of exercise and lower T2 values. However, that study focused only on a single point in time.

Following At-Risk Patients Over Time

In their study, Dr. Link and colleagues analyzed the association between physical activity levels and the evolution of early degenerative cartilage changes in the knee, measuring T2 relaxation times over 4 years in normal people and in those with risk factors for osteoarthritis (such as being overweight, having a family history, and previous knee injury). Occupations that require frequent knee bending are also a risk factor for knee osteoarthritis, Dr. Link said.

The 205 study participants, who were 45 to 60 years of age, were involved in the Osteoarthritis Initiative, a nationwide study funded by the National Institutes of Health.

At study entry, the body mass index (BMI) of the participants ranged from 19 to 27 kg/m², and they had no knee pain (a Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] score of 0).

The participants rated their degree of physical activity on the Physical Activity Scale for the Elderly (PASE) questionnaire. Activity level over the 4 years was averaged and then categorized into 3 tertiles.

T2 values of knee cartilage were measured at the patella, femur, and tibia at baseline and at the 2- and 4-year visits.

The sedentary tertile consisted of the 15% of study participants who walked less than 3 hours per week. The moderate tertile consisted of the 70% who engaged in moderate physical activity (such as moderate walking, golfing, and gardening). The active tertile consisted of the 15% who engaged in very high levels of physical activity (such as running and playing tennis several times a week).

The progression of T2 relaxation times was higher in the active tertile than in the moderate tertile at the medial tibia (2.8 vs 2.0; P = .04) and the patella (4.1 vs 3.1; = .02).

The average T2 relaxation time of all knee compartments was also higher in the active tertile (2.5 vs 2.0; P = .03) than in the moderate tertile. In the analysis, adjustments were made for age, sex, and BMI.

The participants in the sedentary tertile also had greater T2 progression than those in the moderate tertile; however, the differences did not reach statistical significance, Dr. Link reported.

Some limitations of the study include the fact that the PASE questionnaire does not distinguish between weight-bearing and nonweight-bearing activities and that it is subjective, Dr. Link pointed out.

He also stated that T2 relaxation is a relatively new biomarker that needs to be validated in other studies before it can be used in a clinical setting.

For now, it would be wise to counsel patients that moderate activity is best for their knee joints, he said.

"Osteoarthritis is going to be a major challenge as our population gets older," Dr. Link said. "Our older generation wants to be very active, they want to travel, they want to do sports, so they need to try to prevent osteoarthritis at an early stage."

Dr. Link said he sees many patients in the sports clinic at UCSF who have ruined their cartilage from doing aggressive sports.

"I have seen people in their 20s who have completely destroyed their cartilage surface and I wonder what is going to happen to them. They are going to live another 50 or 60 years. They cannot walk on bone, so they will need a total joint replacement, perhaps several, over their lifetime. Each time the bone gets thinner and weaker because bone does not react well to total joint replacement. This is going to become a serious problem," he said.

People need to learn how to protect their joints when they do physical activities, he said. "People should be active, but they should make sure they're exercising in a safe way and not destroying their joints."

Moderation Is "Common Sense"

Dr. Candice Johnstone

Candice Johnstone, MD, MPH, assistant professor of radiation oncology from the Medical College of Wisconsin, Milwaukee, told Medscape Medical News that this research shows how important "common sense" is when doing physical exercise.

"This shows that titrating your physical activity may be important.... Weekend warriors going out and killing themselves...may actually be worse than a moderate amount of exercise, like walking or simple aerobic exercises."

These findings are not particularly surprising, she added.

"Being sedentary is probably not good for your joints because the synovial fluid needs to flow for joint health, and being overly active may not be good for your joints either. There is always a risk/benefit analysis and people are autonomous; they can make those decisions for themselves. This study adds to the information they can use to design their own exercise program," Dr. Johnstone explained.

The study was sponsored by the National Institutes of Health. Dr. Link reports financial relationships with General Electric. The other study authors and Dr. Johnstone have disclosed no relevant financial relationships.

Radiological Society of North America (RSNA) 98th Scientific Assembly and Annual Meeting: Abstract LL-MKS-SU1B. Presented November 26, 2012.