Purpose: Because osteoarthritis may be caused by "wear and tear," we examined the association between level of physical activity and risk of knee osteoarthritis in the elderly.
Subjects and methods: Eligible subjects were participants in the Framingham Heart Study cohort who had radiographically normal knees at biennial exam 18 (1983-1985) and who also completed a physical activity questionnaire at exam 20 (1988-1989). Follow-up knee radiographs were obtained at biennial exam 22 (1992-1993). The study outcomes were the development of incident radiographic or symptomatic knee osteoarthritis between the baseline and follow-up exams.
Results: The number of hours per day of heavy physical activity was associated with the risk of incident radiographic knee osteoarthritis (odds ratio = 1.3 per hour, 95% confidence limits 1.1-1.6, P for trend = 0.006). Adjustment for age, sex, body mass index, weight loss, knee injury, health status, total calorie intake, and smoking strengthened this association (eg, odds ratio for > or = 4 hours heavy physical activity/day compared with no heavy physical activity = 7.0, 95% confidence limits 2.4-20, P for trend = 0.0002). Risk was greatest among individuals in the upper tertile of body mass index (odds ratio for > or = 3 hours/day of heavy physical activity = 13.0, 95% confidence limits 3.3-51). For incident symptomatic knee osteoarthritis, the results were similar, although the number of cases was small. No effects on these outcomes were observed from moderate and light physical activity, number of blocks walked, or number of flights of stairs climbed daily.
Conclusions: Heavy physical activity is an important risk factor for the development of knee osteoarthritis in the elderly, especially among obese individuals. Light and moderate activities do not appear to increase risk.