Taking Fosamax (search) or estrogen for osteoporosis (search) may help protect against knee osteoarthritis, according to a new study.

Osteoarthritis (search) is the most common type of arthritis in the U.S. It causes the breakdown of cartilage between joints. Knee osteoarthritis is common and disabling in many older adults, causing pain, inflammation, and limited joint movement.

In osteoporosis, bones become progressively thin and porous, leading to an increased risk of fracture. It affects more women than men, since women typically have smaller and lighter bones.  Women also lose bone mass at an earlier age and more quickly than men.

Medications to prevent or treat osteoporosis include Fosamax, Evista, (search) and estrogen (search). They work by altering the cycle of bone formation and breakdown.

These drugs were recently studied by researchers including Laura Carbone, MD, MS, of the University of Tennessee Health Center. Carbone and colleagues wanted to find out if these osteoporosis medications had benefits against knee osteoarthritis.

Study participants were about 800 white and black women who were around 75 years old, on average. The women were enrolled in a national, long-term research program called the Health, Aging, and Body Composition Study.

Participants rated their knee pain and had MRI images and X-rays taken of their knees. Once a year, they also brought in all of their medications -- including over-the-counter drugs and supplements -- for the researchers to record.

About 26 percent of the women were using osteoporosis drugs, including 125 on estrogen, 31 on Fosamax, and eight on Evista. Estrogen had been used for the longest period of time: almost 14 years, on average, compared to a little less than two years for Fosamax and Evista use.

Compared with participants who weren't taking osteoporosis medications, users of Fosamax and estrogen had fewer osteoarthritis bone abnormalities in their knees, according to the MRI images. Fosamax, but not estrogen, was also associated with reduced knee pain.

"Our study suggests that [Fosamax] and estrogen may protect against the development of bone abnormalities associated with knee osteoarthritis, which may have a beneficial effect on the overall course of the disease," write the researchers in the November issue of the journal Arthritis & Rheumatism.

Because few black women in the study took osteoporosis medications, the researchers can't promise that the same results apply to that population. They also note that the relatively short-term use of Fosamax and Evista might have an impact on the results of their study.  They say that longer studies are needed to evaluate the potential of using these drugs to treat or prevent osteoarthritis.

"Different relationships might be observed if the drugs had been taken for longer periods of time," they write, calling for further studies on the topic.

Meanwhile, experts say you can do your bones a favor by getting regular exercise to strengthen muscles, tendons, and ligaments that surround knee joints.  They also recommend maintaining a normal healthy weight and getting enough calcium (1,200 mg per day) and vitamin D for bone strength.

By  Miranda Hitti, reviewed by  Brunilda Nazario, MD

SOURCES: Carbone, L. Arthritis & Rheumatism, November 2004; vol 50: pp 3516-3525. WebMD Medical Reference from Healthwise: "Osteoporosis: Topic Overview." WebMD Medical Reference from Healthwise: "Osteoporosis: What Increases Your Risk." News release, John Wiley & Sons, Inc.