A new study, out in Wednesday's Journal of the American Medical Association, has found that knee replacements are on the rise, adding fuel to the Medicare debate.

FOX News Radio's Lisa Brady reports:

Trying to stay active longer, that's the main driver for more knee replacements for seniors.  The number, doubling over a 20-year period among Medicare patients studied.

(Dr. Cram) "If you're an aging patient, this allows you to hike the Appalachian Trail, this allows you to ski, this allows you to run around with your grandkids."

Lead author Dr. Peter Cram at the University of Iowa says obesity is also a factor, along with a rise in Medicare enrollment, adding to concern about healthcare costs.

(Dr. Cram) "We have better therapies today than we have ever had before, but how to allocate those in a way that is affordable and sustainable is an incredibly contentious and difficult debate."

With or without healthcare reform, Cram considers some form of rationing likely.

Lisa Brady, FOX News Radio.