OBJECTIVES:To assess the risk of knee osteoarthritis (OA) attributable to obesity, and the interactions between obesity and other established causes of the disorder.
METHODS:We performed a population-based case ± control study in three health districts of England (Southampton, Portsmouth and North Staffordshire). A total of 525 men and women aged 45 y and over, consecutively listed for surgical treatment of primary knee OA, were compared with 525 controls matched by age, sex and family practitioner. RESULTS: Relative to a body mass index (BMI) of 24.0 ± 24.9 kgam 2 , the risk of knee OA increased progressively from 0.1 (95% CI 0.0 ± 0.5) for a BMI`20 kgam 2 to 13.6 (95% CI 5.1 ± 36.2) for a BMI of 36 kgam 2 or higher. If all overweight and obese people reduced their weight by 5 kg or until their BMI was within the recommended normal range, 24% of surgical cases of knee OA (95% CI 19 ± 27%) might be avoided. As a risk factor for knee OA obesity interacted more than additively with each of Heberden's nodes, earlier knee injury and meniscectomy. In comparison with subjects of normal weight, without Heberden's nodes, and with no history of knee injury, people with a combination of obesity, de®nite Heberden's nodes and previous knee injury had a relative risk of 78 (95% CI 17 ± 354). CONCLUSIONS: Our ®ndings give strong support to public health initiatives aimed at reducing the burden of knee OA by controlling obesity. People undergoing meniscectomy or with a history of knee injury might be a focus for targeted advice.
There is now strong evidence for an occupational hazard of knee OA resulting from prolonged kneeling and squatting. One approach to reducing this risk may lie in the avoidance of obesity in people who perform this sort of work.
Hip osteoarthritis is a major cause of pain and disability. The authors explored individual risk factors for hip osteoarthritis in a population-based case-control study. The study was performed in two English health districts (Portsmouth and North Staffordshire) from 1993 to 1995. A total of 611 patients (210 men and 401 women) listed for hip replacement because of osteoarthritis over an 18-month period were compared with an equal number of controls selected from the general population and individually matched for age, sex, and family practitioner. Information about suspected risk factors was obtained by a questionnaire administered at interview and a short physical examination. Obesity (odds ratio (OR) = 1.7, 95% confidence interval (CI) 1.3-2.4; highest vs. lowest third of body mass index), previous hip injury (OR = 4.3, 95% CI 2.2-8.4), and the presence of Heberden's nodes (OR = 1.6, 95% CI 1.2-2.2) were independent risk factors for hip osteoarthritis among men and women. Hip injury was more closely related to unilateral as compared with bilateral disease. There were a negative association between cigarette smoking and osteoarthritis among men and a weak positive association with prolonged regular sporting activity. Obesity and hip injury are important independent risk factors for hip osteoarthritis, which might be amenable to primary prevention. Hip osteoarthritis may also arise as part of the polyarticular involvement found in generalized osteoarthritis.
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