Over the past two decades, the number of seniors getting total knee replacements has risen by more than 161 percent, according to a nationwide analysis of Medicare beneficiaries.

Researchers from the University of Iowa, Carver College of Medicine believe that the dramatic spike in demand for new knees is primarily being fueled by a rapidly growing elderly population that wishes to remain active in their later years.

Often reserved for seniors whose pain can no longer be mitigated by physical therapy or medications, joint replacement procedures can help aging adults gain greater mobility and find relief from arthritis pain.

Recent advances in knee replacement methods can now provide elders with more durable prosthetics. In 2011, the Food and Drug Administration approved a knee implant meant to last up to thirty years. Surgeons are also currently in the process of testing out the effectiveness of using synthetic cartilage as a total knee replacement alternative.

Evidence indicates that joint replacement surgeries can help older Americans stay healthier longer by allowing them move around and exercise with fewer aches.

A separate investigation, conducted by scientists from Harvard University, found that adults with osteoarthritis may be able to decrease their chances for heart failure by having total knee replacement surgery. Study authors felt that this connection was likely driven by the pain-relieving effects of the procedure, which enabled the aging adults to more easily maintain their physical fitness.

But an increase in medical procedures isn't necessarily a good thing.

University of Iowa researchers feel their study brought up some concerning issues.

The increase in knee replacements also corresponded with a 50 percent decrease in the length of time an elder spent in the hospital following their surgery.

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According to lead author, Peter Cram, M.D., less time in the hospital can increase a senior's risk for complications.

"Our findings highlight the continued concern that declines in hospital length of stay are not a free lunch," Cram says in an interview on the Journal of The American Medical Association website. "We can't continue to reduce hospital length of stay indefinitely without having other complications."

Indeed, over the past ten years, the number of seniors readmitted to the hospital with infections from their knee replacement surgeries has risen.

Cram and his fellow researchers hope the results of their investigation will help encourage doctors and policymakers to develop interventions designed to improve the overall outcome for seniors who need knee replacements.