Is physical activity a risk factor for primary knee or hip replacement due to osteoarthritis? A prospective cohort study.

OBJECTIVE: To estimate prospectively any association between measures of physical activity and the risk of either primary knee or hip replacement due to osteoarthritis (OA).
METHODS: Eligible subjects (n = 39,023) were selected from participants in a prospective cohort study recruited 1990-1994. Primary knee and hip replacement for OA during 2001-2005 was determined by linking the cohort records to the National Joint Replacement Registry. A total physical activity level was computed, incorporating both intensity and frequency for different forms of physical activity obtained by questionnaire at baseline attendance.
RESULTS: There was a dose-response relationship between total physical activity level and the risk of primary knee replacement [hazards ratio (HR) 1.04, 95% CI 1.01-1.07 for an increase of 1 level in total physical activity]. Although vigorous activity frequency was associated with an increased risk of primary knee replacement (HR 1.42, 95% CI 1.08-1.86) for 1-2 times/week and HR 1.24 (95% CI 0.90-1.71) for ≥ 3 times/week), the p for trend was marginal (continuous HR 1.08, 95% CI 1.00-1.16, p = 0.05). The frequency of less vigorous activity or walking was not associated with the risk of primary knee replacement, nor was any measure of physical activity associated with the risk of primary hip replacement.
CONCLUSION: Increasing levels of total physical activity are positively associated with the risk of primary knee but not hip replacement due to OA. Physical activity might affect the knee and hip joints differently depending on the preexisting health status and anatomy of the joint, as well as the sort of physical activity performed.