Total Hip Replacement due to Primary Osteoarthritis in Relation to Cumulative Occupational Exposures and Lifestyle Factors: A Nationwide Nested Case-Control Study

Objective. To investigate the risk of total hip replacement (THR) due to primary osteoarthritis in relation to cumulative occupational mechanical exposures and lifestyle factors. Methods. Using register information, we identified first-time THR cases within the Danish working population in 2005-2006. For each case, 2 age-and sex-matched controls were drawn. Persons within 2,500 randomly selected case-control sets received a questionnaire about job history, weight at age 25 years, present weight and height, smoking, and sports activities at age 25 years. The job history was combined with a job exposure matrix. Cumulative exposure estimates were expressed according to the pack-year concept of smoking (e. g., cumulative lifting was expressed as ton-years). We used conditional logistic regression for statistical analyses. Results. In total, 1,776 case-control sets (71%) were available for analysis. The adjusted odds ratio (OR) for exposure to >= 20 ton-years was 1.35 (95% confidence interval [95% CI] 1.05-1.74) for men and 1.00 (95% CI 0.73-1.41) for women. Standing/walking and whole body vibration showed no associations. The adjusted OR for body mass index (BMI) >= 30 kg/m(2) at age 25 years was 2.44 (95% CI 1.38-4.32) for men and 5.12 (95% CI 2.30-11.39) for women. The corresponding adjusted ORs for an increase in BMI of >= 10 kg/m(2) since age 25 years were 2.16 (95% CI 1.25-3.70) and 2.46 (95% CI 1.47-4.13). Sports participation showed weak positive associations, while pack-years of smoking showed no associations. Conclusion. The results indicated a modest increase in risk of THR in relation to cumulative lifting among men and an increased risk in relation to a high BMI at age 25 years and to a gain in BMI in both sexes.