Impact of Knee Extensor Power on Knee Pain in Adults With or at Risk for Osteoarthritis: The Multicenter Osteoarthritis Study.

OBJECTIVE Knee extensor power declines rapidly with aging and may contribute to knee pain. We evaluated the relationship between knee extensor power and changes in knee pain over 2 years in adults with or at risk for knee osteoarthritis (OA). METHODS We used data from the Multicenter Osteoarthritis Study. Knee extensor power was measured at baseline using isotonic contractions at 40% of one-repetition maximum. Pain severity (Western Ontario and McMaster Universities Osteoarthritis Index; WOMAC) and frequent knee pain (FKP; pain on most days in the past 30 days) were assessed at baseline, 8, 16, and 24 months in each knee. We examined the association between baseline sex-specific quartiles of knee extensor power and two outcomes-worsening WOMAC pain and incident FKP-using logistic regression with generalized estimating equations to account for within-subject correlations between knees. RESULTS Compared to the strongest quartile, the weakest quartile of knee extensor power had 1.35 (95% CI: 0.98-1.86; p for linear trend = 0.04) times the odds of worsening knee pain severity and 1.93 (95% CI: 1.22-3.05; p for linear trend < 0.05) times the odds of incident FKP. CONCLUSION Lower knee extensor power may be a risk factor for both worsening knee pain severity and the development of frequent knee pain in adults with or at risk for knee OA. Interventions targeting knee extensor power may reduce the risk for incident and progressive knee pain.