Successive births, HRT hard on the joints

NEW YORK (Reuters Health) - Early puberty, giving birth to multiple children, and taking hormone replacement therapy (HRT) all increase a woman's risk of needing joint replacement surgery due to arthritis, according to data from a large, study of middle-aged women in the UK.

The findings come from the Million Women Study, in which 1.3 million British women recruited in 1996-2001 at an average age of 56. During an average follow-up of 6 years, approximately 12,000 women had hip replaced and 10,000 had a knee replaced.

Results showed that early menstruation (i.e., younger than 11 years old) increased the likelihood of both needing both types of joint surgery by between 9 percent and 15 percent, while every successive birth increased the risk of needing a new hip by 2 percent and a new knee by 8 percent.

Although use of oral contraceptives did not impact the risk of joint replacement surgery, "current use" of HRT raised the odds of hip replacement by 38 percent and of knee replacement by 58 percent, compared with never having used HRT.

Dr. Bette Liu and colleagues at the University of Oxford report their findings in the Annals of the Rheumatic Diseases, posted online on October 28.

Having a high body mass index (BMI) is known to increase the risk of osteoarthritis and joint replacement, the investigators note in their report, "but it is unlikely that a woman's current BMI would explain the associations found here as ... our findings were consistently observed within subgroups of current BMI."

Nonetheless, Liu's team concludes, "The underlying reasons for these findings remain unclear."

SOURCE: Annals of the Rheumatic Diseases, online October 28, 2008.