Medicine is ever advancing - and that includes orthopedic medicine, which has now developed gender-specific artificial knees that match the subtle anatomical differences between men and women. Technicians have also produced a computer program to assist orthopedic surgeons in correctly positioning replacement knees.

These two elements - gender-specificity and computer-navigated surgery - are being hotly discussed these days whenever orthopedic surgeons come together in professional gatherings.

Dr. Don Serot, an orthopedic surgeon at Lakeland Regional Medical Center in Lakeland, Fla., who operates only on knees, is one example of a physician who is enthusiastic about both new items.

When gender-specific knees for men and women were introduced, he said, he was skeptical. "But I looked at it and examined the models," he said. "I was really surprised at how much better the gender-specific fit."

Male and female bones differ in that men have larger thigh bones and women's knees rotate differently. Those dissimilarities led Zimmer Inc. to develop the gender-specific knees, which the company put on the market almost two years ago.

Zimmer also bought Orthosoft Inc., a Montreal, Quebec, company specializing in medical software, instruments and computerized systems. It made the computer navigation system.

In the operating room, the Orthosoft system, a computer fitted with cameras, reads data from tracking pins inserted in the knee to confirm the surgeon's judgment as to the correct alignment of the artificial implant and the patient's leg.

According to the American Academy of Orthopaedic Surgeons, women had 335,000 knee replacements in the United States in 2005, and

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