WASHINGTON (AP) -- Replacing diseased and painful knees with manmade joints is a highly successful and cost-effective procedure, says a panel of experts.

"It's a major elective surgery that carries a variety of important risks, but it often offers dramatic relief after other therapies fail," Dr. E. Anthony Rankin of Providence Hospital in Washington said Wednesday.

Rankin led the panel, which was assembled by the National Institutes of Health to analyze the risks and benefits of total knee replacement.

The panel found that most patients who undergo the procedure, in which the moving parts of the knee are replaced with a manmade joint, are Medicare beneficiaries, but the age of patients is declining. Today, it is not uncommon for patients in their 50s to receive new mechanical knees.

About 300,000 U.S. patients each year get new knees, and the procedure will become even more common as the American population ages.

The experts found the failure rate of the procedure has been about 1 percent per year over a 20-year period.

"There appears to be rapid and substantial improvement in the patient's pain, functional status and overall health-related quality of life in about 90 percent of patients, and 85 percent of patients are satisfied with the results of the surgery," the report said.

The cost of total knee replacement varies around the country, but the average is about $32,000, including charges for the hospital, the surgeon and the device itself.

The panel found the same racial and ethnic disparities for knee replacement that are seen in other fields of medicine. It called for a study to determine why fewer minorities are getting the surgery.

From 1998-2002, the surgery was performed at the annual rate of 4.8 per 1,000 white males, 3.5 per 1,000 Hispanic males and 1.9 per 1,000 black males, according to Medicare data cited by the report. For women, the rate was 5.9 per 1,000 white women, 5.4 per 1,000 Hispanics and 4.8 per 1,000 black women.

Several factors may be behind the disparity, the panel said, including physicians' beliefs about their patients, limited familiarity with knee replacement in minority communities and patient mistrust of the health care system.

The panel spent three days reviewing the latest medical findings on total knee replacement. The report is a formal assessment that will influence the way doctors treat patients in the United States.

A failure usually happens when the implanted knee loosens, the study found. The experts believe this is primarily caused by a biological reaction to the metal and plastic parts of the device.

A number of different knee prosthesis designs are now available, "but durability and success rates appear roughly similar," the panel concluded.

Total knee replacements tend to be more successful if the patients work with their primary physician and the orthopedic surgeon to prepare for the operation. The experts said preparation would include strengthening of muscles that play key roles in functioning of the knee. Also, obese patients should prepare by losing weight.

"There needs to be a coordinated effort between the patient and his doctors to get a better result," said Sue Karen Donaldson, a professor of physiology at Johns Hopkins University in Baltimore and a member of the advisory panel.

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