But advances in the last decade, particularly in genetics, have led to a fundamental rethinking of osteoarthritis. "The way we think about and research osteoarthritis now is to not be nihilistic or totally negative,"said Dr. Steven Abramson, director of rheumatology at the Hospital for Joint Diseases at New York University. "This is a disease you can intervene in."

Intervention is increasingly needed. Osteoarthritis is incurable, and treatments for it are inadequate. Currently 21 million Americans are coping with the disease, and it is the leading cause of disability in people ages 65 and older. Those numbers are likely to explode as the baby boomers age and as obesity rates rise.

Most patients must rely on oral pain relievers, which provide only temporary or partial relief, or invasive surgery to replace stiff and damaged joints.

New therapies have been slow to arrive, partly because osteoarthritis has been thought of as the result of mechanical wear and tear on the joints. "What we've learned in the last 5 or 10 years is that that's not entirely true," said Dr. Abramson. "There are abnormal chemicals and molecules being produced by these joints that are causing the joint to self-destruct."

The joint damage occurring in osteoarthritis resembles that in rheumatoid arthritis: much of it results from the immune system's misdirected attack on the body's own cells. Screening of rheumatoid arthritis patients for genetic mutations contributing to the process has led to effective medicines that provide relief by inhibiting inflammatory proteins like tumor necrosis factor and interleukin.

Osteoarthritis researchers have been quick to see the possibilities. "Those drugs have revolutionized treatment," Dr. Abramson said. "There are similar molecules in osteoarthritis that might be amenable to drug therapy."