Weight change and the risk of total hip replacement.

BACKGROUND We examined the effect of adult weight change on risk for total hip replacement resulting from primary osteoarthritis, using a prospective study design. METHODS We linked data on body mass index and body weight from 3 screening surveys in 3 Norwegian counties (mean ages at screenings 34, 43, and 47 y; n = 38,868) with follow-up data on total hip replacement (n = 572). Mean age at the start of follow up was 55 years, and mean duration of follow up was 9 years. For each participant we calculated a rate of weight change (weight slope) by linear regression of body weight versus time from the first through the third screening. RESULTS Among men, mean weight change from first to last screening was +9.8 kg in the highest quartile and -3.7 kg in the lowest quartile. In women, the corresponding figures were +9.5 kg in the highest quartile and -5.2 kg in the lowest quartile. There was no association of weight slope, absolute weight change, or relative weight change between screenings with later total hip replacement resulting from primary osteoarthritis. We saw no change in the association between body mass index and later hip arthroplasty as the participants' age increased from 34 to 47 years at the 3 screenings. CONCLUSION The risk for later total hip replacement resulting from primary osteoarthritis was unaffected by weight change during the fourth and fifth decades of life. The dose-response association between adult body mass index and later total hip replacement was similar across these age groups.