Background/Purpose: Regular physical activity (PA) reduces risk of cardiovascular disease, cancer, diabetes, and premature death. Moreover, PA can counteract the reduction in fitness, muscular strength, and endurance associated with aging, prevent or mitigate decline in physical function, and reduce risk and injury from falls. However, whether the increased joint loading associated with certain types or intensity of PA increases the risk of developing knee osteoarthritis (OA), or accelerate the progression of disease is uncertain. Prior studies about PA and knee OA risk used self-reported PA, which is subject to recall and social desirability bias, and activities captured may be limited. We analyzed the association between objectively measured physical activity and risk of developing knee OA in a community-based cohort of middle-aged and older adults.

Methods: We used data from the Osteoarthritis Initiative (OAI), an ongoing prospective cohort study of adults with elevated risk of symptomatic knee OA. Physical activity was measured by a uniaxial accelerometer worn on a waist belt for seven continuous days in two data collection cycles; minutes-per-week of moderate-equivalent intensity physical activity were calculated from these data. Incident knee radiographic OA (ROA), symptomatic OA (sROA), and joint space narrowing (JSN) were analyzed as outcomes. Incident ROA was assessed by Kellgren-Lawrence grade ≥2 in a knee that was KLG 0 or 1 at baseline, and sROA was defined as ROA plus pain, aching, or stiffness in the same knee. We defined knee JSN as ≥1 grade increase in either the medial or lateral tibiofemoral compartments from the previous clinical visit in a knee that did not have Kellgren-Lawrence grade ≥2 with JSN≥1 at baseline. The study population was free of the outcome at baseline (ROA n = 902, sROA n = 1,331, JSN n = 985), and were followed up to four years. Because outcomes were assessed every two years, we used discrete survival analysis and estimated hazard ratios (HR) and 95% confidence intervals (CI). Multivariable analyses adjusted for age, sex, race, body mass index, education, history of knee injury, and hip OA and symptoms.

Results: Participants who met the US Department of Health and Human Services (HHS) recommended physical activity level (≥150 min/week of moderate-intensity equivalent aerobic activity) had neither significantly increased nor decreased hazard of incident radiographic knee OA (HR: 1.57; 95% CI: 0.71–3.45), symptomatic knee OA (HR: 1.37; 95% CI: 0.58–3.21), or joint space narrowing (HR: 0.78; 95% CI: 0.35–1.72), compared with those who did not meet recommendations.

Conclusion: Meeting physical activity guidelines was not associated with the risk of developing knee OA or joint space narrowing over up to four years of follow up among OAI participants. Given the proven benefits of physical activity on joint health and general health, our results support the HHS physical activity recommendations to adults.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/objectively-measured-physical-activity-and-risk-of-knee-osteoarthritis-the-osteoarthritis-initiative/