Dr. Parratte and his research team studied 218 patients between the ages of 18 and 90 who had total knee replacements at the Mayo Clinic and who admitted to their doctors that they either did heavy manual labor or took part in a high-impact sports that their doctor recommended they avoid.

That group was compared to 317 people in a control group who also had the surgery using the same implant but followed their doctors' recommendations and avoided high-impact activity.

Doctors evaluated all the participants’ implants and discovered that there were no significant radiological differences or differences in the durability of the implants between the groups.

“It’s all about probabilities,” says Jason Dragoo, MD, an assistant professor of orthopaedic surgery at Stanford University Medical Center in Palo Alto, Calif., who specializes in sports medicine. “So what it’s saying is if you really look at each knee replacement and you do those sports, you can have a 10 percent increase risk of having a failure if you do the sports.

“There may be an increased risk, but it’s minimal,” he continues. “So patients have to decide if that’s worth it for them to lead a more active lifestyle.”

Dr. Dragoo says he welcomes this study because it validates what he and other doctors have been hearing from patients for years.

“There have been anecdotal reports that many clinics have been allowing their patients to do activities like skiing and playing tennis, there have been good results,” Dr. Dragoo says. “What this paper does is test this claim with scientific rigor. “

So why aren’t high-impact sports affecting the implant after seven-and-a-half years? Dr. Parratte and his team say it’s likely due in part to better-made prostheses that are thicker and stronger than ones produced years ago. He also thinks the patients have something to do with it.

“The patients practicing these kinds of sports were probably doing it before the prosthetics so they have experience and probably are more able to protect the prosthesis,” he explains. “They probably are doing it more carefully and paying attention to their knees.”

Researchers did find one high-impact sport that hurt patients – so-called power lifting, which involves squatting and then lifting a bar with lots of weights off the ground and over your head.

“That’s very bad for the knee. Two patients in the series were practicing and both needed a revision,” Dr. Parratte says. “All the charges are going through the knee in a bad manner and it’s hundreds of pounds on the knee in a short amount of time.“