Occupational lifting is associated with hip osteoarthritis: A Japanese case-control study

Objective. Hip osteoarthritis (OA) is a frequent cause of pain and disabili ty in Western countries, but the disorder is less common in Japan. A case-c ontrol study in Britain found obesity, hip injury, and occupational lifting to be associated with hip OA among men and women. However, there are few e pidemiological studies concerning factors associated with hip OA in Japan. We performed a comparable case-control study of the disorder in Japan, and contrasted the findings with those from Britain. Methods. The study was carried out in 2 health districts in Wakayama Prefec ture, Japan. Cases were men and women aged greater than or equal to 45 year s listed for total hip arthroplasty due to OA over one year, and who did no t have an established cause of secondary OA (e.g., rheumatoid arthritis, an kylosing spondylitis). For each case, a control was selected randomly from the general population and was individually matched to the case for age, se x, and district of residence. Cases and controls were interviewed with a st ructured questionnaire about medical history, physical activity, socioecono mic factors, and occupation. Measurements were made of height and weight. Results. One hundred fourteen cases (103 women, 11 men) were compared with 114 controls. We found no relationship between obesity and hip OA (OR = 1.0 , 95% CI 0.5-1.9; highest vs lowest thirds of distribution of body mass ind ex). There was, however, a statistically significant association between oc cupational lifting and hip OA, such that regular lifting of 25 kg in the in dividual's first job (OR = 3.6, 95% CI 1.3-9.7) or of 50 kg in their main j ob (OR = 4.0, 95% CI 1.1-14.2) was associated with increased risk of hip OA . These associations remained after adjustment for potential confounding va riables. In contrast, those subjects who spent > 2 h each day sitting durin g their first job were significantly less likely to have the disorder (crud e OR = 0.5, 95% CI 0.3-0.9). This association also remained statistically s ignificant after adjustment for potential risk factors. Conclusion. Our findings support the hypothesis that occupational physical activity, particularly the lifting of very heavy loads in the workplace at regular intervals, predisposes to hip OA in both Britain and Japan. The lac k of association between obesity or hand involvement and hip OA in Japan su ggests that the contribution of constitutional and mechanical risk factors to this disorder might differ in different populations. However, attention to manual handling in the workplace would appear an important aspect of pre ventive strategies against hip OA in Western and Oriental populations.