Level of physical activity and the risk of radiographic and symptomatic knee osteoarthritis in the elderly: The Framingham Study

PURPOSE: Because osteoarthritis may be caused by "wear and tear," we examin ed the association between level of physical activity and risk of knee oste oarthritis 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 e xam 22 (1992-1993). The study outcomes were the development of incident rad iographic or symptomatic knee osteoarthritis between the baseline and follo w-up exams. RESULTS: The number of hours per day of heavy physical activity was associa ted 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). Adjust ment for age, sex, body mass index, weight loss, knee injury, health status , total calorie intake, and smoking strengthened this association (eg, odds ratio for greater than or equal to 4 hours heavy physical activity/day com pared 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 ter tile of body mass index (odds ratio for greater than or equal to 3 hours/da y of heavy physical activity = 13.0, 95% confidence limits 3.3-51). For inc ident symptomatic knee osteoarthritis, the results were similar, although t he number of cases was small. No effects on these outcomes were observed fr om 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 de velopment of knee osteoarthritis in the elderly, especially among obese ind ividuals. Light and moderate activities do not appear to increase risk. Am J Med. 1999;106: 151-157. (C) 1999 by Excerpta Medica, Inc.