Knee Surgeries Surge in Seniors; So Do Problems

Sept. 26, 2012— -- Knee replacement rates among Medicare patients have increased sharply over the past two decades -- as have rates of hospital readmissions and revision complications associated with the procedures -- a study showed.

The number of total knee arthroplasty (TKA) procedures went up 162 percent -- 243,802 -- from 1991 to 2010 and the per capita rate rose 99 percent -- to 62.1 per 10,000 enrollees, according to an analysis of fee-for-service Medicare records by Dr. Peter Cram of the University of Iowa in Iowa City and colleagues.

Shorter hospital stays posted over the period were offset by rising readmissions and complications in revision procedures, particularly wound infections, the group reported in the Sept. 26 issue of the Journal of the American Medical Association.

"This growth is likely driven by a combination of factors including an expansion in the types of patients considered likely to benefit from TKA, an aging population, and an increasing prevalence of certain conditions that predispose patients to osteoarthritis, most notably obesity," they wrote.

An accompanying editorial also cited greater demand for an active lifestyle among seniors.

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"While there are different contributing factors, more importantly this report may be describing only the surface of what is expected to be a profound increase in knee arthroplasty over the next 30 years," warned editorialists Dr. James Slover and Dr. Joseph D. Zuckerman, both of the Hospital for Joint Diseases of New York University Langone Medical Center.

At a cost of around $15,000 per procedure, the strain this will place on Medicare and other insurers is clear.

"When you multiply $15,000 by that volume of procedures you're talking about major money even by federal Medicare standards and this is a real challenge for the federal government," Cram said in a video interview released by the journal.

His group analyzed a cohort of 3.3 million Medicare Part A beneficiaries ages 65 and older who had a primary knee replacement and 318,563 who had a revision procedure.

Trends in utilization from 1991 to 2010, showed a:

162 percent increase in the total volume of primary procedures, from 93,230 to 243,802

106 percent rise in revision TKA volume, from 9,650 to 19,871

99 percent increase in the per capita rate of primary knee replacement, from 31.2 to 62.1 per 10,000 Medicare enrollees

59 percent increase in per capita revision procedures, from 3.2 to 5.1 per 10,000 Medicare enrollees

However, it's not clear whether the growth "represents growth in appropriate use of a highly effective procedure or overuse of a highly reimbursed procedure for which indications still depend on clinical judgment," the researchers wrote.

"It is likely that both factors are at play," they suggested, although they noted a recent slowing in the rate of growth of primary and revision procedures.

Hospital length of stay fell from an average of eight days for a primary knee replacement in the 1991-1994 period to four days in 2007-2010 and from nine days to five for revision procedures over the same time frames.

That shift likely reflected changes in the payment system that were a powerful incentive to hospitals to quickly discharge patients home or to post-acute care settings, like skilled nursing facilities, Cram's group noted.

Although this may have helped keep costs down in one respect, it may have raised them in another because of the trade-off between length of stay and readmissions, they added.

All-cause 30-day readmissions rose from 4 percent to 5 percent for primary procedures and from 6 percent to 9 percent for revision procedures.

Readmissions for adverse events were relatively stable over the two decades studied for primary knee replacement but that was not the case for revisions.

Revision procedures were associated with a more than doubling in readmission rates for wound infection from 1 percent to 3 percent and a more than 100 percent increase in readmissions for hemorrhage, sepsis, and heart attack.

Patients who returned to the hospital soon after their procedure were older and more likely to be male, black, and sicker with comorbidities.

Notably, centers that did more knee replacements were associated with lower readmission rates for both primary and revision procedures.

A significant percentage of TKAs are performed by surgeons doing fewer than 12 cases a year, the editorialists noted.

"Therefore, careful consideration should be given to whether the majority of these cases should be shifted toward high-volume centers, which often have the infrastructure and the experience needed to develop the highly coordinated care pathways necessary to optimize the quality outcomes and efficiency of the episode of care for complex patients," they suggested.

The researchers acknowledged that their findings may not extrapolate to the 40 percent of the TKA population not under fee-for-service Medicare and noted the limitations of administrative data including lack of outcome data such as functional status and patient satisfaction.