No link between recreational physical activity, development of knee osteoarthritis
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Physical activity, defined as recreational whole-body physiological energy expenditure, and time spent in physical activity are not associated with knee osteoarthritis outcomes, according to data published in Arthritis & Rheumatology.
“While there are some well-established risk factors for knee OA including joint injury, obesity and female sex, the effect of [physical activity (PA)] on the risk of OA is unclear,” Lucy S. Gates, PhD, of the University of Southampton, in the United Kingdom, and colleagues wrote. “There is evidence to suggest that PA in the form of exercise improves clinical outcomes among those with OA. There is also evidence to suggest that some types of PA are a potential risk factor for the development of structural change at the knee.”
“Further research is required to examine the components of PA and using different metrics of PA,” they added. “This may help to advance our understanding of the biomechanical and pathophysiological changes that occur with PA which may ultimately help identify and explain the threshold between risk and protection. It is important to identify the role of PA in disabling diseases such as OA and to inform prevention strategies targeted to reduce the global burden of OA and encourage, where appropriate, participation in PA for the benefits of overall health.”
To examine the relationship between recreational physical activity and knee OA outcomes using comparable definitions for both physical activity and OA, Gates and colleagues conducted a meta-analysis of patient-level data from six global cohorts. Eligible participants demonstrated no evidence of knee OA or rheumatoid arthritis at baseline and were followed for 5 to 12 years. Assessed outcomes included radiographic knee OA — defined as a Kellgren Lawrence score of at least two — painful radiographic knee OA — defined as radiographic OA with knee pain — and OA-related knee pain.
The participants self-reported physical activity, which included sport, walking and cycling activities, quantified at baseline as metabolic equivalents of tasks (METS) in days per week. The researchers calculated and pooled risk ratios using an individual participant data meta-analysis. In a secondary analysis, Gates and colleagues examined the link between physical activity, as defined as the number of hours per week spent in recreational activity, and knee OA outcomes. A total of 5,065 participants were included in the study.
According to the researchers, the pooled risk ratio estimates for MET days per week and painful radiographic knee OA (1.02; 95% CI, 0.93-1.12), radiographic OA (1; 95% CI, 0.94-1.07) and OA-related knee pain (1; 95% CI, 0.96-1.04) were not significant. In addition, there were no significant associations for any outcome found in the secondary analysis of hours per week spent in physical activity.
“This is the first study to assess the relationship between PA defined as MET days/wk and knee OA,” Gates and colleagues wrote. “These findings suggest that PA as defined by whole-body, physiological energy expenditure during sport/walking/cycling activities is not associated with knee OA. Likewise, time spent in recreational PA is not associated with incident knee OA.”
“Further investigation with clear disaggregation between all components of PA (including type of activity, intensity, frequency and duration) over a lifetime would be of most use, however incredibly difficult to obtain such robust data,” they added. “Given what we also know about the effects of manual occupation on knee OA it would be useful to understand the association between activities according to loading, along with relative lifetime volume (intensity and duration) on knee OA using prospective investigation.”
Perspective
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David A. McLain, MD, MACR, FACP, FRCP
These researchers undertook a daunting task in this study: Combining six independent observational osteoarthritis (OA) cohort databases to analyze whether recreational physical activity (PA) was a risk factor for knee OA. Since these were independent studies, they had their own entry criteria, definitions (even the definitions of OA and PA), data collection fields and follow-up. For example, some cohorts had X-rays available, and some did not.
Physical activity, usually self-reported, varied from patients with extensive activity in the Framingham cohort to patients with very little activity in other cohorts – presumably as some cohorts did not record “light activity.”
Occupation-related physical activity could not be assessed in most of the cohorts. This has been shown to be a significant factor in the development of knee OA. The authors concede all these points. They converted various physical activities to MET days/week and is the first study to do so in evaluating knee OA and PA.
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