MONDAY, Oct. 27 (HealthDay News) -- Early puberty, having lots of children, and hormone replacement therapy all increase a woman's likelihood of having knee or hip replacement surgery, according to a study that looked at 1.3 million British women whose health was tracked for an average of six years after they turned 50.

The participants, all taking part in the Million Women Study, were asked how old they were when they had their first and last periods, how many children they'd given birth to, and whether they'd used oral contraceptives and hormone replacement therapy (HRT).

During the six years of monitoring, more than 12,000 of the women needed a hip replacement and almost 10,000 needed a knee replacement. The researchers concluded that starting menstruation at or before the age of 11 increased the probability of knee and hip replacement by between 9 percent and 15 percent. Each successive birth increased the risk of knee replacement by 8 percent and the likelihood of hip replacement by 2 percent.

Previous use of oral contraceptives had no effect on joint surgery risk, but current use of HRT was linked with a 58 percent increased chance of knee replacement and a 38 percent greater likelihood of hip replacement. However, the researchers noted that better use of health services by women on HRT may explain this association.

The findings, published online ahead of print in the Annals of the Rheumatic Diseases, suggested that estrogen and other female sex hormones may be among the reasons why women were more likely than men to have osteoarthritis, particularly of the knee.

More information

The National Institute of Arthritis and Musculoskeletal and Skin Diseases has more about joint replacement.