The incision itself is quite simple — only 4 to 5 inches are needed to open a knee.

But then the shaving begins. Slowly bone is scraped away, until the back of the kneecap, end of the thighbone, and top of the shinbone are left bare of arthritis. Still crippled and bent, the surgeon must release ligaments until the knee can once again straighten. Only then do doctors use cement to attach an implant to the end of the thighbone and top of the shinbone.

“[My knee] was in pretty bad shape,” said Tom Akin, a local resident who received a knee replacement in November 2004. “It was bowed out to the exterior. [The replacement] has given me back a normal lifestyle.”

In the past 20 years, the number of knee replacements has more then doubled, and that number is expected to rise.

“The number of surgeries being performed per year has gone up dramatically over the past 20 years,” said Associate Professor Peter Cram, the lead author of a study released on Sept. 26 by the University of Iowa Carver College of Medicine.

In fact, it has more than doubled, putting stress on the health-care system.

“We are so booked right now doing joint replacements, we can’t even take care of everyone that needs one done,” said John Callaghan, a UI professor of orthopaedic surgery. “It’s to the point that we are actually overwhelmed by it.”

Every year, roughly 600,000 knee-replacement surgeries are performed in the United Sates, according to the study. With a cost of roughly $15,000 per surgery, that amounts to $9 million.

Because 60 percent of knee replacements are done in patients over 65, Medicare is picking up a lot of that bill.

That leaves many professionals worried.

“I think Medicare is a tremendous program for the elderly people in the U.S. The problem is as the cost of medicine goes up, is it going to be sustainable?” Callaghan said.

The fear resides in the idea of rationing. If the cost of knee replacements becomes too much for Medicare to pay for, it may decrease how much it is willing to reimburse a patient, which would effectively limit how many people are able to receive new knees.

“We are an aging society,” Cram said. “We have tons of really good surgeries, but they are expensive.”

Patrick Barron, a UI adjunct lecturer in economics, believes rationing will probably happen with knee replacements.

“We are just going to see more shortages,” he said. “Despite what we say, there really are limited medical resources.”

The reason for the increase in demand is complicated and contains many facets. According to the study, the increase is due to an aging population. Within that population, there is also an increase in those that see a benefit in the surgery and request one, which is called an increase in the per capita utilization.

“It is the most common elective surgery we do in the U.S.,” Cram said.

Callaghan agreed the aging population contributes to the continuing increase, but believes there are other factors involved.

“More patients come to us with bad arthritis of their knees because they have a lot of friends that have had the operation, have seen how well they’ve done — people like Tom Akin,” he said. “In addition, the surgeon has more confidence in the surgery today because the implants are better and the techniques of putting them in have been perfected with minimal complications. And over-riding this is the obesity epidemic. It is well known that arthritis of the knee occurs a lot more frequently in obese patients, and that’s why the per capita utilization is up.”

Callaghan said he believes it would be a shame if knee replacement surgeries were rationed.

“We hope that we will be able to continue to serve those that need it,” he said.