Knee Replacements Not Harmed by Most Sports

A study suggests high-impact activities don't contribute to the early failure of knee implants.


Doctors have long recommended that knee replacement patients avoid sports like football, soccer, aerobics, jogging, baseball and basketball because it was thought that high-impact activities might contribute to the early failure of artificial joints, leading to the need for a second surgery. 

But a study suggests that those long-held assumptions could be wrong.

The study compared two groups of people with knee implants  – those who ignored advice to take it easy on their new joints (called the sport group) and model patients who followed doctors' orders to avoid high-impact activities (the control group). 

Researchers found that after more than seven years there were no significant differences in wear or mechanical failure between the two groups.

The research was presented at the 2010 annual meeting of the American Academy of Orthopaedic Surgeons in New Orleans, La.

“We were a little bit surprised because we were not thinking that there would be absolutely no difference,” says lead author Sebastian Parratte, MD, PhD, an orthopaedic surgeon from the Mayo Clinic in Rochester, Minn., and the Aix-Marseille University, Center for Arthritis Surgery, Hospital Sainte-Marguerite in Marseille, France.

“Before, everybody was thinking if you go running or something like that it will kill the prosthetic and don’t do that. It’s forbidden,” Dr. Parratte says

Perhaps even more surprising is that researchers found that those who took part in the non-recommended sports actually showed higher knee and function scores than the control group.

The control group had a higher rate of loosening, wear, fracture and overall mechanical implant failure than the sport group at 11 percent compared to 8.5 percent in the sport group.

Adjusting for a variety of lifestyle factors, doctors say the sport group had a 10 percent increased risk of mechanical failure, but they don’t consider that to be statistically significant.

“The big news is that everybody before was thinking that doing high-activity sports would be terrible for the prosthetic of the patient and what we discovered was it was not terrible and indeed the patients that did high-level activity sports were doing better than others,” Dr. Parratte says.  

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.“  

Dr. Dragoo says he does see one shortcoming with this study and that’s the fact that patients were only assessed after seven-and-a-half years.

“It’s medium-term follow-up. But what we really need to do is show at 15 or 20 years, these implants are failing at the same rate, high impact or not. We need additional reports before we can come to the overall conclusion that this higher impact activity is safe,” Dr. Dragoo says. “But intermediate follow-up lends credence to the idea that more activity is OK for implants. It’s worthwhile reporting even though it doesn’t conclusively prove they are safe.”

Bashir A. Zikria, MD, an assistant professor in the Department of Orthopaedics at Johns Hopkins University Medical Center who specializes in sports medicine also has concern about how long these study participants were followed. “It’s only seven-and-a-half years. The thing you worry the most about is long-term. As far as wear, you don’t know wear analysis for at least 10 years,” Dr. Zikria says.

So for now, Dr. Zikria says this study doesn’t make him want to change his recommendations to patients who’ve had total knee replacements.

“If they tell me at 15 years there’s no difference in the two groups of people then maybe I would change my opinion. But at seven-and-a-half years, it wouldn’t change the way I practice,” Dr. Zikria says.  “Just because something is good in the short-term doesn’t mean it will be good in the long-term.”

Dr. Parratte understands that it is too early to expect doctors to change their recommendations for knee replacement patients when it comes to what sports they should and should not take part in. But he says if further studies back up these results, it could happen someday.

“It’s good news for the patient, good news for the surgeon; and we have to keep on working on this for the future,” Dr. Parratte says.

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