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

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Abstract
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/m2versus a BMI of 20.5–21.9 kg/m2was 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/m2in 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.