NEW YORK, Mar 22 (Reuters Health) - Hormone replacement therapy after menopause is known to help prevent and treat the bone-thinning disease osteoporosis. Now new research suggests it also prevents the loss of cartilage that cushions the knee joint, possibly warding off arthritis.

In a study of 81 postmenopausal women, Australian researchers found that long-time users of estrogen replacement therapy (ERT) showed thicker cartilage in the knee joint compared with women who had never been on ERT. Cartilage is connective tissue that cushions the ends of bones within a joint. Because arthritis is marked by the breakdown of cartilage, ERT may offer a defense against the debilitating disease, according to the report in the April issue of the Annals of Rheumatic Diseases.

Osteoarthritis is the most common form of arthritis among the elderly, striking more than 20 million American adults. The affected joints become inflamed, stiff and painful. When the disease occurs in weight-bearing joints like the knees, it can be debilitating. Obesity is considered a risk factor for knee osteoarthritis, as is a history of injuries to the joint.

Whether ERT might be a factor in osteoarthritis risk is controversial, according to Flavia M. Cicuttini of Monash University in Prahran, Victoria, and her colleagues. But some research has suggested ERT reduces the risk of the condition in the hip and knee.

Cicuttini's team used MRI scans to gauge the volume of knee cartilage among the women, about half of whom had used ERT for at least 5 years. The rest of the women had never been on the therapy. The investigators found that, on average, cartilage thickness was about 8% greater among ERT users.

Both groups of women were similar in terms of body weight, prior knee injury, exercise and other factors that might affect joint health.

"This is the first study to show that women on ERT have more knee cartilage than those that don't take ERT, suggesting that ERT may protect women against developing osteoporosis," Cicuttini told Reuters Health. However, she added, more long-term research is needed before hormone replacement is prescribed for reducing the risk of arthritis.

The reason for the connection is unclear, Cicuttini said, but hormone replacement may protect cartilage from wearing away, just as it does for bone mass.

Researchers are just beginning to look into whether hormone replacement therapy benefits connective tissue, which includes cartilage, ligaments and tendons, Dr. Theodore Oegema of the University of Minnesota in Minneapolis, told Reuters Health.

One reason the idea is new is because older women with very thin bones have been shown to be at low risk for arthritis in the knee and hip. So, according to Oegema, there was little reason to believe that a treatment that boosts bone mass, like ERT, would also protect against arthritis.

But, Oegema said, it is possible that for the "vast majority" of older women, ERT might protect against both osteoporosis and arthritis. "It's a very interesting idea," he said. "And it will be great if it's true."

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