Unisex Replacement Knees Are Fine for Women

Knee replacement is a big business—more than half a million such operations were performed in 2005, according to the American Academy of Orthopaedic Surgeons. The group is holding its annual meeting in San Francisco this week, and two knee-replacement-related studies that were released there caught my attention.

The first deals with one of the major controversies in joint replacement: whether women, because of their smaller stature and different physiology, do better with knee replacements tailored specifically to them. When I wrote about this last year, one of the arguments I heard was that women typically do worse after knee replacement surgery, perhaps because their unisex implants don't fit correctly. Alternatively, it may be because, compared with men, they often put off the surgery until they're in worse condition. (The New York Times had a nice summary of a recent study looking at women delaying surgery.)

But the study presented at the AAOS meeting suggests that the regular implants don't produce worse outcomes for women after all. It examined records from almost 21,000 people—more than 13,000 women and over 7,000 men, both about 68 years old on average. After surgery, the two genders' range of motion, pain scores, and rate of revision (do-over surgeries) were similar. "There is no scientific evidence that women aren't doing as well as men," says Timothy Brox, an orthopedic surgeon with Kaiser Permanente in Fresno, Calif., and an author of the study. And if the existing outcomes are fine, that means there's no use for a gender-specific implant.

Another study tweaks conventional wisdom about the kind of exercise people can do once they've had their knee replaced. To reduce the pounding and strain on the new joint, doctors usually recommend low-impact activities like golf or walking rather than high-impact activities like running. But researchers at Scripps Clinic in La Jolla, Calif., reported that a golf swing can generate about as much force on an artificial knee, if it's in the forward knee, as jogging one step. That's not reason to give up golf, however; the number of golf swings in 18 holes is far, far smaller than the number of footfalls in a typical jog. And while golfing may irritate the knee and cause swelling, it's not the same kind of pounding that can actually wear out an artificial joint.

But golfers with artificial knees should at least be aware that their favorite activity may be a cause of knee pain. The solution? Work to modify your swing to put less strain on the forward knee. And if you are looking for something else to do, try biking on a stationary bike, which the study showed was a great way to get aerobic exercise and built up the quadriceps without straining the knee.