Arthritis is the name for a group of conditions that affect the joints. Two important kinds are osteoarthritis and rheumatoid arthritis. Osteoarthritis is the most common form of the disease. It's caused by a degeneration, or wear and tear, on the affected joints. Normally, the ends of the bones that meet in a joint are covered with a protective layer of tough tissue, called cartilage. In osteoarthritis the cartilage breaks down and the ends of the bones rub together during movement. This leads to pain, inflammation and stiffness. The Arthritis Foundation estimates about 27 million Americans have osteoarthritis.

Rheumatoid arthritis is characterized by inflammation of the lining of a joint. It's believed to be caused by an autoimmune disorder, in which the body mistakenly attacks its own tissues. In early stages, the lining swells, causing pain, stiffness, redness, warmth and swelling around the joint. Over time, the lining thickens. Eventually, the inflammation leads to the destruction of cartilage and bone in the affected joints. The joint may lose its shape and mobility. Rheumatoid arthritis affects 1.3 million Americans.

Knee Replacement

A knee replacement is the surgical removal of a damaged or diseased knee joint and replacement with an artificial joint, or prosthesis. The American College of Rheumatology reports 418,000 total knee replacements were performed in the U.S. in 2003. As our population ages, the incidence of arthritis and the need for knee replacement are expected to increase. A recent article in American Medical News estimates 1.4 million knee replacements will be performed in 2015.

Usually, doctors recommend a knee replacement when traditional therapies no longer provide relief and knee pain becomes serious or interferes with daily activities. Yet, some people either are unwilling to have the surgery, or wait until they have severe symptoms or are unable to function. A few years ago, a study in the New England Journal of Medicine found women were three times more likely than men to delay knee replacement. A more recent study in the Canadian Medical Association Journal reports doctors are more likely to recommend knee replacement for men than to women.

Avoiding the Delay

Lynn Snyder-Mackler, P.T., Sc.D., a Physical Therapist at the University of Delaware and her colleagues recently evaluated 221 men and women who were candidates for knee replacement surgery. Several tests of function were performed. The researchers found women tended to have weaker thigh muscle strength, less function and greater disability than men. In addition, women were likely to have more advanced disease.

Snyder-Mackler says patients who have poor function and weakness prior to surgery tend to have poorer outcomes after surgery. So it's important to get an evaluation and consider knee replacement before the symptoms become severely debilitating. A physical therapist can perform several tests to get an objective measure of function and degree of disability.

Snyder-Mackler says, in the past, doctors often advised patients to wait because knee prostheses often wear out, requiring a second, more difficult replacement. However, today, there are improved surgical techniques and more variations in sizes to enable surgeons to get a better fit. There is even a knee prosthesis that is specifically designed for women.

For general information on knee arthritis and joint replacement:

American Academy of Orthopaedic Surgeons, public website

American College of Rheumatology

Arthritis Foundation

National Institute of Arthritis and Musculoskeletal and Skin Diseases