We used published guidelines of the Meta-analysis of Observational Studies in Epidemiology Group (MOOSE) to perform the meta-analysis. The search strategy employed included computerized bibliographic searches of MEDLINE, PubMed, EMBASE, The Cochran Library and references of published manuscripts. Study-specific incremental estimates were standardized to determine the risk of knee osteoarthritis associated with a 5 kg/m2 increase in BMI.
Twenty-one studies were included in the study. The results showed that body mass index was significantly positive associated with osteoarthritis risk in knee site. A 5-unit increase in body mass index was associated with an 35 % increased risk of knee osteoarthritis (RR: 1.35; 95 % CI: 1.21, 1.51). Magnitude of the association was significantly stronger in women than that in men with significant difference (men, RR: 1.22; 95 % CI: 1.19, 1.25; women, RR: 1.38; 95 % CI: 1.23, 1.54; p = 0.04). The summary effect size was 1.25(95 % CI: 1.18, 1.32) in case-control studies and 1.37 (95 % CI: 1.19, 1.56) in cohort studies (p = 0.28). Body mass index was positively associated with knee osteoarthritis defined by radiography and/or clinical symptom (RR: 1.25, 95 % CI: 1.17, 1.35) and clinical surgery (RR: 1.54, 95 % CI: 1.29, 1.83). The latter tended to be stronger than the former (p < 0.01).
Increased body mass index contribute to a substantially increased risk of knee OA. The magnitude of the association varies by sex and OA definition.