The number of total knee replacementsurgeries has soared 161.5% among Medicare participants over the past 20years, a $5 billion annual tab that will continue to grow as the USA's77 million Baby Boomers age, according to a large study out today.

Thewider use of knee replacement, on one hand, is good news for therapidly aging population. But while knee surgery eases pain from severearthritis and improves quality of life, the improvements "can be viewedas another strain on government, individuals,and businesses strugglingwith unremitting growth in health care costs,'' the authors report inthe Journal of the American Medical Association.

"Peopleare living longer and want to be active," says lead author Peter Cram."They feel great after this surgery. They can hike in the mountains andski. They can be active with their grandchildren." The challenges, headds, are how to address post-surgery problems that can develop fromshorter hospital stays and in patients with other conditions such asdiabetes and obesity, and how to ensure doctors are not overusing a"highly reimbursed procedure."

A knee replacement costs Medicareabout $15,000, costs that would be higher, the authors find, hadMedicare not taken cost-lowering measures of shortening hospital staysand relocating many rehabilitations from in-patient clinics into thepatients' homes. However, those strategies can lead to problems down theroad for some patients and add costs and longer recovery times.

Thestudy is the first to evaluate trends and outcomes linked to total kneereplacement, the authors write, and includes a breakdown of expensivefactors that can lead to rehospitalizations and additional surgeries.

From1991 to 2010, 3.27 million patients ages 65 and older had total kneereplacements and 318,563 had knee revisions, additional surgery to fixproblems. The researchers found the number of primary replacements amongMedicare patients increased from 93,230 in 1991 to 243,802 in 2010 (anincrease of 161.5%). The number of revisions increased from 9,650 to19,871. Total knee replacement surgeries increased 99.2% (31.2procedures per 10,000 Medicare enrollees in 1991 to 62.1 procedures per10,000 in 2010.)

"We not only have more peopleaging than we did 20 years ago, but we have more of these surgeriesbeing performed,'' says Cram, a physician at the University of IowaCarver College of Medicine in Iowa City.

During the same timeperiod, length of hospital stay decreased from 7.9 days to 3.5 days fortotal knee replacement and from 8.9 to five days for revisions. However,re-admissions have increased slightly for total knee replacements buthave increased more than 100% for revisions.

"Revisions are amuch more complicated surgery,'' says Cram, "and we need to be thinkingmore about which patients are suited for them and which ones aren't."

Inan accompanying editorial, the authors say the yearly demand for totalknee replacements could be as high as 3.48 million procedures by 2030and can potentially "decrease the allocation of health care resourcesused by patients."

Yet the surgeries also "will be a driver ofhealth care costs,'' and steps need to be taken to address "predisposingmodifiable factors such as obesity and to advance efforts at earlyintervention strategies to treat mild arthritis and to preventprogression'' requiring surgery.