Women with osteoarthritis (OA) who take hormone replacement therapy (HRT) for at least six months after total hip or knee replacement surgery cut their risk of revision surgery – a second, do-over surgery – by almost 40 percent, according to a new British study published online in Annals of the Rheumatic Diseases. Taking HRT for a year or more cuts the risk in half.

Lead researcher Nigel Arden, MD, director of musculoskeletal epidemiology at the University of Oxford, in England, says it is the first published study “describing the effect of HRT on prosthesis survival in women undergoing hip or knee replacement.”

The implications are important because the rate of joint replacements is skyrocketing – the result of an aging population and the rise in obesity, which puts extra stress on joints. More than one million hip and knee replacements are performed each year in the United States. By 2030, the number of knee replacements alone is expected to approach 3.5 million annually.

But not all artificial joints last as long as they should – typically 10 to 20 years. According to the American Academy of Orthopaedic Surgeons, around 10 percent wear out sooner – often in the first five years. Failed implants must be removed and replaced with new components in what is known as revision surgery, which is often less successful and more expensive than the original procedure.

Implants fail for several reasons but the most common is osteolysis, which occurs when small particles from the implant cause an inflammatory response that destroys the supporting bone.

Researchers have tried various strategies to prevent bone loss around implants, including bisphosphonates such as risedronate (Actonel), alendronate (Fosamax) and ibandronate (Boniva) – drugs commonly used to treat osteoporosis. Although results of bisphosphonate trials have been mixed, Dr. Arden and colleagues found that patients taking them had a nearly twofold increase in implant survival.

Bisphosphonates are associated with rare but serious side effects, however, including atypical thigh fractures and destruction of bone tissue in the jaw (jaw osteocronosis). So the researchers decided to look at HRT, which is used to relieve symptoms of menopause, including thinning bones.

“There is evidence that drugs like hormone replacement therapy might have a beneficial effect on implant survival comparable to [a bisphosphonate],” Dr. Arden says.