Total knee replacement is a very common and safe surgery that’s used to relieve severe pain and disability caused by knee osteoarthritis, and to improve patients’ quality of life. However, it’s also very expensive at approximately $15,000 per procedure. With an estimated 600,000 total knee replacements performed annually in the United States, the aggregate annual cost for total knee replacement (also known as total knee arthroplasty or TKA) is $9 billion.

Researchers at the University of Iowa Roy J. and Lucille A. Carver College of Medicine studied trends in TKA surgeries over a 20-year period from 1991 to 2010 and found a tremendous growth in the number of TKAs performed on the U.S. Medicare population. The study, published Sept. 26 in the Journal of the American Medical Association (JAMA), suggests the growth is driven by both the increase in the number of older Americans and increased demand among older adults for total knee replacements.

Peter Cram

“For policymakers, a main finding of the study was the dramatic growth we saw in the number of first time TKAs done in this population of Medicare patients,” says Peter Cram, UI professor of internal medicine and lead study author. “The growth was driven by an aging population—there simply are many more adults over age 65 now than there were 20 years ago—and within this population, demand of this procedure has doubled.”

Cram notes that the growth also reflects the success of the total knee replacements as well as an increased desire by older adults to maintain a more active lifestyle.

“This is an incredibly effective surgery. Although it is a major surgery, it is extremely well tolerated and it allows people to remain active as they age,” he says. “But the increase in numbers means that this procedure represents a major health care expense for the Medicare program.

“Our findings highlight the challenge of controlling costs in an aging population that wants the highest quality care possible,” Cram adds.

The analysis included 3,271,851 Medicare patients (age 65 years or older) who underwent first-time TKA and 318,563 who underwent revision TKA.

The researchers found that the number of first time knee replacements increased more than two-and-a-half times from 93,230 in 1991 to 243,802 in 2010, while per capita utilization doubled from 31.2 procedures per 10,000 Medicare enrollees in 1991 to 62.1 procedures per 10,000 in 2010.

In addition, the number of revision TKA procedures more than doubled from 9,650 in 1991 to 19,871 in 2010 and per capita use of the procedure increased by almost 60 percent.

Cram noted a second important finding of the study was the decrease in the number of days TKA patients spend in the hospital following surgery (also known as length of stay). During the 20-year study period, length of stay decreased from approximately eight to four days. At the same time, the study showed an increase in rates of readmission.

Brian Wolf

“We are discharging patients sooner after their surgery because of the incentives that Medicare places upon the hospital, physician, and medical team,” says Brian Wolf, UI professor of orthopaedics and rehabilitation and senior author on the study. “It’s not surprising that with increasingly shortened hospital stays, more patients are being readmitted after discharge.”

The study showed all-cause 30-day readmission rates increased from 4.2 percent in 1991-1994 to 5.0 percent in 2007-2010. For revision TKA, a decrease in hospital length of stay was accompanied by an increase in all-cause 30-day readmission from 6 percent to 9 percent and an increase in readmission for wound infection from 1.4 percent to 3.0 percent.

“Patients should be aware that discharge is likely to happen within a few days of the surgery and that there is a chance of readmission due to problems,” Cram says.

“Readmission is also a cost to hospitals, and increased readmission rates eliminate some of the cost savings achieved by shortening the initial length of stay.”

In addition to Cram and Wolf, researchers involved in the study included Xin Lu with UI Health Care; Stephen Kates and Yue Li at the University of Rochester; and Jasvinder Singh at the University of Alabama at Birmingham.

The study was funded in part by grants from the National Institutes of Health.