Relationship of height, weight and body mass index to the risk of hip and knee replacements in middle-aged women

OBJECTIVES: To examine the effect of height, weight and body mass index (BMI) on the risk of hip and knee replacement in middle-aged women. METHODS: In a prospective cohort study 490 532 women aged 50-69 yrs who were recruited in the UK in 1996-2001 were followed over 2.9 yrs for incident primary hip and knee replacements. RESULTS: Height, weight and BMI were all associated with the risk of hip and knee replacement. Comparing the tallest group (>/=170 cm) with the shortest (/= 30 kg/m(2)) to women with a BMI < 22.5 kg/m(2), the relative risks for hip and knee replacement were 2.47 (95%CI 2.11-2.89) and 10.51 (95%CI 7.85-14.08), respectively. These effects did not vary according to age, education, alcohol and tobacco consumption, or with use of hormonal therapies. Currently, an estimated 27% of hip replacements and 69% of knee replacements in middle-aged women in the UK are attributable to obesity. CONCLUSION: In middle-aged women, the risk of having a hip or knee replacement increases with both increasing height and increasing BMI. From a clinical perspective, relatively small increases in average BMI among middle-aged women are likely to have a substantial impact on the already increasing rates of joint replacement in the UK