If you’ve had a total knee replacement, you can expect it to hold up and allow you to remain active for at least 20 years, according to new research presented at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons in February.

“We’ve known for years that total knee replacement adds to quality of life, adds to patients being more active, being able to participate in things they want to participate in,” says study author John Meding, MD, an attending orthopaedic surgeon at The Center for Hip and Knee Surgery in Mooresville, Ind. “But we also know that over time as we age, function diminishes. You get slower. [So] we were somewhat surprised at the activity level of these people at 20 years or more after total knee replacements.”

Dr. Meding says most 80-year-olds without knee replacements rate 6 out of 10 on an activity level scale. That means they can walk around, go out to dinner and get in and out of a car. But among those who had knee replacements 20 years earlier, the average activity score was 8.3 – “which basically says they are regularly very active, participating in things like golf, swimming, riding a bike,” Dr. Meding says. “That was probably the most surprising thing in the study.”

The study relied on data collected between 1975 and 1989 at The Center for Hip and Knee Surgery on more than 1,700 total knee replacements. Of those subjects, 128 were alive for a 20-year follow up. Most had osteoarthritis, were female and had their operation when they were 63 years old on average. Researchers used this group to evaluate walking and stair climbing ability. The participants were an average of 82 years old during the follow-up.

Researchers found that 95 of the subjects could walk at least five blocks and almost half of them could walk as much as they wanted. All but two could go up and down stairs without holding on to a wall or banister, and only three in the group were housebound. None of the implants had failed at the 20-year mark.

“This basically confirmed our suspicion that people were active, but we were not expecting this level of activity,” Dr. Meding says.

Steven B. Haas, MD, is chief of knee service at the Hospital for Special Surgery in New York City and a professor of orthopaedic surgery at Weill Cornell Medical College. He would have liked the study to compare and contrast participants’ activity levels with a control group of people in the same age group who didn’t have knee replacements. Still, he says this study should be reassuring to patients who had total knee replacements decades ago. Patients with more modern knee replacements should feel even more optimistic, he adds, because the implants in this study were far more rudimentary than those used today.

“Back then you had to fit the patient to the implant, but now they are very closely matched to natural anatomy,” Dr. Haas explains. “The implants we’re doing now, we’re hopeful they may last 30 years, because the implant materials are so much better than they were before.”

Dr. Haas says he thinks this information is particularly important because patients receiving total knee replacements these days are even younger than in the past.

“There is a huge growth in patients who need implants earlier – in their 50s instead of 60s,” Dr. Haas says. “Some people think knee replacements last 10 or 15 years. No, these are likely to last 20 or more years,” he adds. “Most people passed away with their implants. The vast majority had them last a lifetime.”