Monday November 30 2009
The research did not look directly at arthritis but at knee health
“Middle-aged men and women may be risking arthritis if they overdo their exercise regime,” the BBC reported. It said a study of people aged 45 to 55 found that those who did more exercise were also more likely to have knee damage.
This story is from research presented at the annual conference of the Radiological Society of North America (RSNA). The study looked at MRI scans of the knees of more than 200 people, and found an association between knee abnormalities and reported levels of physical activity. The study has not been published yet, and this appraisal is based on the limited information available. However, it is known that this is a cross-sectional study, a type of study design that can only show an association, and not that one thing causes another. It also did not assess the type of exercise undertaken.
The findings of an association are not surprising. The Arthritis Research Campaign has said: "We have known for years that certain high impact sports and jobs are associated with an increased risk of osteoarthritis, particularly of the knee. But for the vast majority of people, exercise is good, not only for the cartilage but for total body health.”
Where did the story come from?
The study was carried out by Dr Christoph Stehling and colleagues affiliated to the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, and the Department of Clinical Radiology at the University of Muenster, Germany. The study was recently presented at the RSNA annual conference.
The research has not been published in a peer-reviewed journal. This article is based on an abstract of the presentation and a press release by the RSNA. It is not a full critical appraisal. There is no indication of who funded the work.
What kind of research was this?
This was a cross-sectional study that assessed physical activity levels and knee health in a group of middle-aged individuals.
What did the research involve?
The conference abstract reports that the researchers ‘analysed’ 236 people aged between 45 and 55, 136 of whom were women. It is not clear how these people were recruited to the study, but the researchers note that they were all without knee pain and had a BMI between 19 and 27, i.e. none were overweight or obese.
A questionnaire called the Physical Activity Scale for the Elderly (PASE) was used to determine activity levels in all participants. Their knee health was assessed using different types of MRI scans. These images were then rated by two musculoskeletal radiologists who graded cartilage, meniscal, ligamentous and other knee abnormalities, using a scoring system known as the Whole Organ Magnetic Resonance Imaging Score (WORMS scores).
What were the basic results?
In 47% of the subjects, there was evidence of meniscal lesions (tears in one or both of the half moon-shaped pieces of cartilage/fibrous tissue), 75% had cartilage lesions, 40% showed evidence of bone marrow oedema (abnormalities in the central portion of the bone marrow), and 17% had evidence of damage to the knee ligaments.
When the researchers analysed the damage relative to how much exercise the person said they had, they found an association between increasing levels of exercise and increasing incidence of knee damage.
How did the researchers interpret the results?
The researchers concluded that middle-aged non-symptomatic individuals had a high prevalence of knee abnormalities, including cartilage and meniscus lesions. Those with higher levels of physical activity had a higher number and more severe grade of knee abnormalities.
The abstract has limited information on how the participants were selected or how the study was carried out. Until more detail is available, a full critical appraisal is not possible. However, it is possible to deduce the following:
- This is a cross-sectional study, a type of study that can only show associations and cannot prove causation. It can demonstrate how prevalent knee abnormalities were in a sample of middle-aged people, and can suggest that there is an association between levels of exercise and incidence and severity of knee injuries. However, it cannot prove that one causes the other. It’s possible that people with bad knees are simply less likely to exercise.
- It is also important to note that the participants in this study did not have knee pain. This suggests that while they seemed to have exercise-associated knee abnormalities, this was not affecting their quality of life.
- This study did not actually assess arthritis as an outcome. It looked at the association between knee abnormalities and exercise in people without knee pain. Linking the observed knee abnormalities to arthritis is an inappropriate extrapolation of these results, therefore conclusions cannot be drawn about a link between exercise and arthritis. In fact, there is some evidence that land-based therapeutic exercises reduce knee pain and improve physical function for people with knee osteoarthritis in the short term.
Findings that higher levels of physical activity are associated with knee abnormalities are not surprising. Sports that have a high impact on the joints, such as running, are known to be linked to knee injury. However, there are alternatives such as swimming and cycling.
The Arthritis Research Campaign said: "We have known for years that certain high-impact sports and jobs are associated with an increased risk of osteoarthritis, particularly of the knee. But for the vast majority of people, exercise is good, not only for the cartilage but for total body health.”