Serial Motherhood and HRT Boost Likelihood of Knee Replacement

They were quizzed about how old they were when they had their first and last periods, how many children they had given birth to, and whether they had used oral contraceptives and hormone replacement therapy (HRT).

On average, they were monitored for six years, to see whether they were admitted to hospital for a knee or hip replacement for the inflammatory joint disease, osteoarthritis.

During this period, more than 12,000 of them needed a hip replacement and just under 10,000 a knee replacement.

Starting menstruation at or before the age of 11 boosted the probability of both types of surgery by between 9% and 15%.

Every successive birth also increased the risk of a hip replacement by 2%, and that of a knee replacement by 8%.

And although previous use of oral contraceptives did not affect the risk of joint surgery, current use of HRT boosted the chances of a hip replacement by 38% and of a knee replacement by 58% compared with those who had never used HRT.