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Lifespan and Success of Artificial Hip, Knee Implants Unpredictable

Oct 7, 2008 | Parker Waichman Alonso LLP

A surprising number of people who receive artificial hips and knees will need to have their joints replaced, according to a recently-released study.  What's more, another study has found that there is no way to predict what kind of activities might put too much wear and tear on a new hip or knee implant.

Knee and hip replacement surgery has become wildly popular.  According to the Associated Press, Americans undergo 478,000 knee replacements and 234,000 hip replacements every year.  But by 2030, hip replacements are expected to double, and knee replacements are expected to reach a whopping 3.4 million per year.  

Such surgeries are popular because, when successful, they can relieve patients of their debilitating pain, and allow them to walk normally again.  But joint implants have a finite lifespan, and will eventually need to be replaced.   Often substandard implants - as illustrated by this year's recalls of Stryker Hip Implants and Zimmer Durom Cup Hip Implants - result in the need for early revision.  But even quality implants won't last forever.

The first study, conducted by British researchers, found that one in 75 people who undergo hip or knee replacement surgery must undergo surgical revision within three years.  Even with the best of care, such replacement surgery is not always avoidable.

The one-in-75 replacement figure cited by the British researchers is actually pretty good, but the study found that the number of revisions gets higher, depending on several factors.  For example, hip resurfacing, a popular procedure, where rather than cutting away damaged bone, damaged hip ball and socket is covered with smooth metal, required revision at a higher rate than the traditional operation.  According to the report, 2.6 percent of resurfacing patients got a redo in three years compared with just under 1 percent who got a cemented new hip.

Patients with a partial knee replacement called the unicondylar knee needed more revisions than those who undergo a more traditional procedure.  The rate of a revision with that procedure was about 2.8 percent.

A second study, conducted by researchers at Massachusetts' Lahey Clinic found that there is no evidence available right now to enable doctors to advise patients on what activities might be safest for their new joint.  While most doctors will tell their patients that low-impact activities, such as walking and jogging are fine, there is no agreement on more strenuous sports.  There is also no evidence that hip resurfacing - typically offered to younger patients - will enable a return to more strenuous activities than traditional hip replacement.

"People do have very high expectations. They're not always getting those results," Thomas Barber of the American Academy of Orthopaedic Surgeons, told the Associated Press.   "If you didn't play tennis before you got the operation, you're probably not going to play tennis afterwards."