Reduced functional performance in the lower extremity predicted radiographic knee osteoarthritis five years later.

BACKGROUND Reduced quadriceps strength is an early finding in subjects with knee osteoarthritis, but it is not clear whether it is a cause or a consequence of knee osteoarthritis. OBJECTIVE To determine whether reduced functional performance in the lower extremity predicts the incidence or progression of radiographic knee osteoarthritis. DESIGN Prospective, epidemiological, population based cohort study. PATIENTS 148 subjects (62 women), aged 35-54 (mean 44.8), with chronic knee pain from a population based cohort. MEASUREMENTS Predictors analysed were age, sex, body mass index, baseline knee pain, and three tests of lower extremity functional performance: maximum number of one-leg rises from sitting, time spent walking 300 m, and timed standing on one leg. Weightbearing tibiofemoral knee radiographs were obtained at baseline and after 5 years (median 5.1, range 4.2-6.1), and classified according to Kellgren and Lawrence as no osteoarthritis (Kellgren and Lawrence = 0, n = 94) or prevalent osteoarthritis (Kellgren and Lawrence >/=1, n = 54). RESULTS Fewer one-leg rises (median 17 v 25) predicted incident radiographic osteoarthritis five years later (OR 2.6, 95% CI 1.1 to 6.0). The association remained significant after controlling for age, sex, body mass index, and pain. No significant predictor of radiographic progression in the group with prevalent osteoarthritis was found. CONCLUSION Reduced functional performance in the lower extremity predicted development of radiographic knee osteoarthritis 5 years later among people aged 35-55 with chronic knee pain and normal radiographs at baseline. These findings suggest that a test of one-leg rises may be useful, and interventions aimed at improving functional performance may be protective against development of knee osteoarthritis.