A New Knee Built for Women Only
The pitch: The female body needs its own design
Manufacturers of everything from running shoes to deodorants design products specifically for women. One of the latest entries: the first artificial joint created for-and heavily advertised to-females. Doctors say it's too soon to tell whether the Gender Knee represents a giant leap for womankind or if it gives its maker, Zimmer Holdings Inc., a leg up in the market.
In the case of the knees, according to Zimmer, here's how men and women are different: First, the patella, or kneecap, is thinner in women. Also, women's wider hips create a different angle between the pelvis and knee, which can mean the kneecap gets pulled to the side when the quadriceps contract. And the end of the thighbone is typically narrower in men. Most prosthetic knees were modeled on the male anatomy-which may explain why knee replacements in women aren't as successful when measured by reported pain and do-over rates.
But will the new (and more expensive) replacement actually serve women better? "In theory, yes, but the evidence isn't there," says Kimberly Templeton, an associate professor of orthopedic surgery at the University of Kansas Medical Center and a spokesperson for the American Academy of Orthopaedic Surgeons. Sheryl Conley, Zimmer's chief marketing officer, says seven studies now underway will look at patient satisfaction and range of motion. Preliminary data will be available in a year or so. Anatomical differences aside, Templeton says, replacement knees may underperform in women in part because females tend to delay surgery-sometimes until they're housebound by disability.
In addition, it's not clear that the manufacturer's specialized design will translate to less pain, says Steven Haas, an orthopedic surgeon and chief of the knee service at the Hospital for Special Surgery in New York. For example, making the front of the replacement knee thinner by one twenty-fifth of an inch won't necessarily make a noticeable difference to recipients. Having a correctly fitted device is clearly important, says Haas, who notes that other companies have modified their smaller knees to account for gender differences in anatomy. (Haas has consulted with Smith & Nephew, a rival to Zimmer.)
More important, says Haas, is to find a skillful surgeon. Differences between implants, he argues, are relatively minor compared to the technique of the surgeon putting them in.
This story appears in the August 13, 2007 print edition of U.S. News & World Report.