To examine longitudinal patterns in body mass index (BMI) over 14 years and its association with knee pain in the Chingford Study.
We studied a total of 594 women with BMI data from clinic visits at years (Y) 1, 5, 10, and 15. Knee pain at Y15 was assessed by questionnaire. Associations between BMI over 14 years and knee pain at Y15 were examined using logistic regression.
BMI significantly increased from Y1 to Y15 (P < 0.0005) with medians (interquartile ranges) of 24.5 kg/m(2)  (22.5-27.2 kg/m(2) ) and 26.5 kg/m(2)  (23.9-30.1 kg/m(2) ), respectively. At Y15, 45.1% of subjects had knee pain. A greater BMI at Y1 (odds ratio [OR] 1.34, 95% confidence interval [95% CI] 1.05-1.69), at Y15 (OR 1.34, 95% CI 1.10-1.61), and change in BMI over 15 years (OR 1.40, 95% CI 1.00-1.93) were significant predictors of knee pain at Y15 (P < 0.05). BMI change was associated with bilateral (OR 1.61, 95% CI 1.05-1.76, P = 0.024) but not unilateral knee pain (OR 1.22, 95% CI 0.73-1.76, P = 0.298). The association between BMI change and knee pain was independent of radiographic knee osteoarthritis (OA). The strength of association between BMI and knee pain at Y15 was similar during followup measurements.
Over 14 years, a higher BMI predicts knee pain at Y15 in women, independently of radiographic knee OA. When adjusted, the association was significant in bilateral, not unilateral, knee pain, suggesting alternative pathologic mechanisms may exist. The longitudinal effect of BMI on knee pain at Y15 is equally important at any time point, which may assist reducing the population burden of knee pain.