New joints: Unclear how much pounding new hips, knees can take

WASHINGTON — One in 75 patients who gets a knee or hip replaced must get it replaced again within three years, new research finds, although the studies underscore a question: Just how much pounding can a new joint take if you want it to last?

First-time hip and knee replacements are skyrocketing, for good reason. They can be highly successful at relieving debilitating pain and helping people to walk normally again.

Also on the rise are more complex "revisions" where doctors remove the initial joint implant and put in another. That repeat operation isn't always avoidable even with high-quality care.

But new research suggests the type of joint replacement you choose and even gender can play a role in whether you need a revision. And as people seeking new joints increasingly are younger and more active, a second new study issues a caution about what athletic activity patients should try after recovery.

"I would discourage high impact activities including running, jumping or plyometrics (sports performance enhancement)," said Jacob Pattengill, a physical therapist and manager at Select Physical Therapy in Cape Girardeau. "Safe exercises usually include cycling, swimming, walking and hiking."

But you should ask your personal physician for specific guidelines.

Dr. Thomas Barber of the American Academy of Orthopedic Surgeons and a surgeon in Oakland, Calif., got tough with a patient who wanted a hip replacement so he could return to coaching basketball. Coach from the sidelines, don't play, Barber advised. "Yes, you can run up and down the court with your kids. But I really don't want you in there jumping up and down and throwing balls."

Americans are undergoing more than 478,000 knee replacements a year, a number expected to reach 3.4 million by 2030 as the population ages. The AAOS counts 234,000 total hip replacements a year, expected to more than double by 2030.

As the country ages and battles arthritis and obesity, joint replacements in younger patients will likely increase and "the likelihood of outliving these artificial joint will become more and more common," Pattengill said.

Already, 40,000 knee revisions and 46,000 hip revisions were done in 2004, the latest data available. Knee revisions are expected to increase sevenfold, and hip revisions to more than double, by 2030. Revisions are tougher operations, taking longer as surgeons hunt for usable bone. They also cost more. A hip replacement averages $35,000, compared with $45,000 for a revision, according to AAOS.

British researchers took the closest look yet at how modern joint replacements are holding up, using a registry tracking the operations in England and Wales since 2003. That overall one-in-75 revision rate is considered pretty good, they reported last month in the journal PLoS Medicine.

The U.S. has no nationwide registry, but high-volume U.S. hospitals report similar revision rates, and perhaps a little worse at less experienced facilities, said AAOS' Barber.

A bigger question is how the implants hold up at five years or longer. Some implants tend to fail early if they're going to at all, so rates may stabilize.

Nor could the study measure how much wear-and-tear patients put on new joints.

Enter the second study. Researchers at Massachusetts' Lahey Clinic reviewed the science to date and concluded there's no good evidence to guide advice on what activities are worst for a joint's life span. Among findings in this month's Journal of Bone and Joint Surgery:

• Twisting and hard landings are of particular concern.
• Surgeons generally recommend low-impact walking, cycling, swimming, golf or bowling — and advise against high-impact football, basketball, jogging and soccer. There's no agreement on others, such as baseball and singles tennis.
• Hip resurfacing is targeted to younger, more athletic patients but there's no proof that they return to sports more safely than patients with traditional hip replacement.

"People do have very high expectations. They're not always getting those results," Barber said.

Dr. Brian C. Schafer, a surgeon with Orthopaedic Associates of Southeast Missouri PC who performs revision surgery, said the numbers and studies can be skewed if they include numbers for partial knee replacements, which doctors know have a short shelf life. New designs and techniques are extending the years, he said.

"The main thing is to limit impact and stress on the joint through weight control and avoiding high impact activities," he said.

Local quotes were added using the Southeast Missourian's health community listserv.