Knee Replacements: Are You Too Young, Too Old, Too Fat, or Too Active?

The implants have improved, yet patients are also more demanding

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Getting a new knee because the original has worn out and may have become painfully arthritic is an increasingly common surgery in America. First-time knee replacement surgeries rose 63 percent between 1997 and 2004, according to a 2008 paper in Arthritis Care & Research. If that clip keeps up, some 1.4 million such surgeries will be performed in 2015, the researchers estimated.

Findings coming out of the 2010 American Academy of Orthopaedic Surgeons annual meeting this month are shedding helpful light on knee replacements, including how active one can be with an artificial knee, how young or how old one should be to undergo the surgery, and the varying benefits to be gained. 

[Read 6 Alternatives to Arthroscopic Knee Surgery.] 

When patients and their doctors decide whether to proceed with a knee replacement, "it's always a quality-of-life issue," says Mark Figgie, chief of the Surgical Arthritis Service at Hospital for Special Surgery in New York. Osteoarthritis, which causes the cartilage in joints to wear away, is the usual culprit when knee pain has made walking painful. Even sleeping can be very uncomfortable—sometimes unbearably so—because a day's worth of moving around has inflamed the joint. And being unable to enjoy the activities you once did—say, golf or cycling—also can be a quality-of-life factor, says Figgie. 

Whereas patients used to have knee replacements in their late 60s or later, Figgie says he now is more often doing the procedure in folks in their 50s—and not infrequently, in patients in their 40s. The standard practice used to be that younger patients with knee trouble would be prescribed painkillers or be given steroid injections for several years to tide them over until surgery. Indeed, information presented at the AAOS meeting today found that the average age for Americans getting total knee replacements has declined. Comparing the years from 1990 to 1994 with 2002 to 2006, researchers learned that the average age has gone from 70 years to 68. 

Experts see several forces at work. "Now we've got better materials and we're more comfortable doing [total knee replacements] in patients younger than 60 or 65," says Michele D'Apuzzo, an orthopedic surgery resident at the Mayo Clinic in Rochester, Minn., and lead author of the study. In particular, the plastics being used to replace the worn-out cartilage and serve as a cushion in the knee joint have improved. Still, the younger patients having these surgeries will likely live another 20 to 30 years, and the data on how well these improved components will last, says D'Apuzzo, is "not there yet." 

In addition, folks' expectations of continued mobility and activity have risen. Not only do aging baby boomers expect to keep doing the things that can really put pressure and strain on joints—like tennis, skiing, or jogging—but younger people, too, don't want to wait for a knee fix if the technology is available now. Research presented at this year's AAOS meeting suggests, however, that even the activities that the Knee Society, a professional group for knee specialists, currently considers a no-no after knee replacement may be OK for some individuals. These activities are ones that pound on the knee and put the most pressure on the joint, like singles tennis, running, soccer, and football. 

"We were expecting patients who practiced impact sports would have terrible complications," says Sebastien Parratte, an orthopedic surgeon who was doing a one-year fellowship at the Mayo Clinic when the study was performed. That was not the case, however. The results showed no significant differences after 7.5 years of follow-up in patients who stayed away from the not-recommended sports and patients who played them anyway. 

The surprising results, Parratte says, were "reassuring, but it's only one study. It's not enough to change the recommendation." He notes, however, that while the Knee Society says patients can do less punishing activities, like cycling or swimming, they are not officially recommended. Perhaps it's time to consider recommending such gentler activities, says Parratte, since the subjects in the trial that fared best after knee replacement were the least likely to be obese or have diabetes or cardiovascular disease. "They are healthier and practice sports," he says. Indeed, Figgie notes that generally speaking, people who do best after a knee replacement are in good shape: "It's better to be fit than fat," he says.