Body mass index, a measure of relative weight, is increasingly recognized as an important risk factor for osteoarthritis, especially in weight bearing joints. The objective was to assess the association between body mass index and hip osteoarthritis susceptibility and investigate the difference between sex, study type and osteoarthritis definition.

We did electronic searches of Medline, Embase and Cochrane library from the commencement to December 2009. A meta-analysis and meta-regression was executed to quantitatively assess the strength of associations between body mass index and hip osteoarthritis risk. Study-specific incremental estimates were standardized to determine the risk associated with a 5kg/m² increase in body mass index.

Fourteen epidemiological studies were included. Our study showed that body mass index was significantly positive associated with hip osteoarthritis risk. A 5-unit increase in body mass index was related to an increased risk of hip osteoarthritis (RR: 1.11; 95%CI: 1.07, 1.16). The magnitudes of associations were similar in women as compared with men (women, RR: 1.10; 95%CI: 1.05, 1.15; men, RR: 1.08; 95%CI: 1.04, 1.12; p>0.05). The summary estimates were 1.12 (95%CI: 1.02, 1.24) in case-control studies and 1.11 (95%CI: 1.06, 1.16) in cohort studies (p>0.05). Body mass index was positively associated with hip osteoarthritis defined by radiography and/or clinical symptom (RR: 1.04; 95%CI: 1.00, 1.07) and clinical surgery (RR: 1.16; 95%CI: 1.11, 1.22) with no significant difference (p>0.05).

Increased body mass index contributes to a positive effect on susceptibility to hip osteoarthritis. Associations between body mass index and hip osteoarthritis risk do not vary by sex, study design or osteoarthritis definition.