Obesity, physically demanding work and traumatic knee injury are major risk factors for knee osteoarthritis--a population-based study with a follow-up of 22 years.

OBJECTIVE Several studies have shown that knee OA is associated with obesity, physical stress at work, traumatic knee injuries, heredity and female gender. However, the body of such evidence comes from cross-sectional or case-control studies, and from only a few follow-up studies, mostly of short duration. Based on the nationwide Mini-Finland Health Survey, we analysed the potential risk factors for prediction of incident knee OA in the long term. METHODS Focused on major health problems, the survey was carried out in 1978-80 in a sample of 8000 subjects, representative of the Finnish population aged > or =30 years. Altogether 823 subjects free from knee OA at the baseline were re-examined in 2000-01, and after the intervening 22 years 94 new cases of knee OA were found. Knee OA was diagnosed on both occasions by physicians using information on disease histories, symptoms and standardized clinical examinations. RESULTS The risk of developing knee OA was strongly associated with BMI (kg/m(2)); adjusted for age and gender and other covariates, and compared with the reference category (BMI < 25.0); the relative odds ratios (ORs) with 95% CIs were 1.7 (95% CI 1.0, 2.8) and 7.0 (95% CI 3.5, 14.10) for subjects with BMIs 25.0-29.9 and > or =30.0, respectively. Similarly, the adjusted OR for the heaviest category of physical stress at work was 18.3 (95% CI 4.2, 79.4) compared with the lightest category, and 5.1 (95% CI 1.4, 19.0) for permanent complaints due to past knee injury. CONCLUSIONS This prospective study confirms the roles of obesity, heavy work load and knee injury in the aetiology of knee OA.