The impact of body mass index on later total hip arthroplasty for primary osteoarthritis - A cohort study in 1.2 million persons

Objective. To investigate the effects of body mass index (BMI), height, and age on the risk of later total hip arthroplasty for primary osteoarthritis (OA). Methods. We matched screening data on body height and weight from 1,152,006 persons ages 18-67 years who attended a compulsory screening for tuberculosis in 1963-1975 with data from the Norwegian Arthroplasty Register for the years 1987-2003. We identified 28,425 total hip replacements because of primary OA. Results. We found dose-response associations between both height and BMI and later hip arthroplasty. The relative risk (RR) among men with a BMI >= 32 kg/m(2) versus a BMI of 20.5-21.9 kg/m(2) was 3.4 (95% confidence interval [95% CI] 2.9-4.0). The corresponding RR in women was 2.3 (95% CI 2.1-2.4). There was a decreasing trend in the RR with an increasing age at screening. Among men, the RR for an increase of 5 kg/m(2) in the BMI was 2.1 (95% CI 1.7-2.5) when measured at age <25 years and 1.5 (95% CI 1.3-1.7) when measured at ages 55-59 years. Among women, the corresponding RR values were 1.7 (95% CI 1.5-1.9) and 1.1 (95% CI 1.1-1.2). Conclusion. There was a strong dose-response association between BMI and later total arthroplasty for OA of the hip. Being overweight entailed the highest RR among young participants, and the participants who were overweight at a young age maintained an excess RR for arthroplasty throughout the followup period.