Knee Replacement: Hospital Days Down, Readmissions Up

Janis C. Kelly

September 25, 2012

September 25, 2012 — Efforts to reduce costs by discharging patients who have total knee replacements (TKRs) sooner have largely succeeded, but shorter length of stay (LOS) is associated with a rise in readmissions, according to Peter Cram, MD, MBA, from the University of Iowa Carver College of Medicine, Iowa City, and colleagues.

Using Medicare data, Dr. Cram reports in an article published in the September 26 issue of JAMA that increases in TKR volume were driven by increases both in the number of Medicare enrollees and in per capita use. The researchers also raise the question of whether the recent surge in primary TKR will be followed during the next 10 to 15 years by an increase in the need for revision TKR, which is a much more expensive and difficult procedure.

Dr. Cram told Medscape Medical News, "For about the past 15 years, Medicare and other insurers have created incentives for hospitals to discharge patients as quickly as possible because of incredible pressure to constrain healthcare spending. The good news is that those incentives worked. We have lowered hospital LOS dramatically.

"The bad news," he continued, "is that when you discharge people more quickly, they sometimes get home or to a rehab or nursing facility and need to come back. This illustrates the 'squeezing the balloon' or 'whack-a-mole' phenomenon of trying to control healthcare costs. The overall message is that you can't keep reducing LOS without expecting something to happen. We've reduced LOS [for TKR] probably about as far as we can."

Approximately 600,000 TKR procedures are performed annually in the United States at a cost of approximately $15,000 per procedure, according to the authors, for a total cost of $9 billion/year.

In the current analysis, the researchers analyzed trends in primary and revision TKR volume, per capita use, and outcomes in the US Medicare population for the period between 1991 and 2010. The analysis included 3,271,851 patients aged 65 years or older who underwent primary TKR and 318,563 patients who underwent revision TKR identified in Medicare Part A data files.

Primary TKA procedures increased 161.5%, from 93,230 in 1991 to 243,802 in 2010. Per capita use increased 99.2% (from 31.2 procedures/10,000 Medicare enrollees in 1991 to 62.1 procedures/10,000 enrollees in 2010).

Revision TKR procedures increased 105.9%, from 9650 in 1991 to 19,871 in 2010, and per capita use of revision TKR increased 59.4%, from 3.2 procedures per 10,000 Medicare enrollees in 1991 to 5.1 procedures per 10,000 in 2010.

Obesity more than doubled among patients undergoing primary TKR, from a prevalence of 4.0% to 11.5% during this time.

The average hospital LOS for primary TKR declined from 7.9 days (95% CI, 7.8 - 7.9) between 1991 and 1994 to 3.5 days (95% CI, 3.5 - 3.5) between 2007 and 2010, for a relative decline of 55.7% (P < .001). Meanwhile, all-cause 30-day readmission rates increased from 4.2% (95% CI, 4.1% - 4.2%) between 1991 and 1994 to 5.0% (95% CI, 4.9% - 5.0%) between 2007 and 2010.

For revision TKR, decreased LOS was accompanied by an increase in all-cause 30-day readmission, from 6.1% (95% CI, 5.9% - 6.4%) to 8.9% (95% CI, 8.7% - 9.2%; P < .001), and an increase in readmission for wound infection from 1.4% (95% CI, 1.3% - 1.5%) to 3.0% (95% CI, 2.9% - 3.1%; P < .001).

"No Easy Answers"

Dr. Cram commented, "This illustrates the incredible difficulty, and to some degree the desperation, involved in controlling healthcare spending. There are no easy answers."

Elena Losina, PhD, codirector of the Orthopaedics and Arthritis Center for Outcomes Research at Brigham and Women's Hospital, associate professor of orthopedics at Harvard Medical School, and associate professor of biostatistics, Boston University School of Public Health, Massachusetts, reviewed the study for Medscape Medical News.

Dr. Losina said, "I think that increase in per capita utilization plays a greater role than the increase in the number of Medicare enrollees.... The increase in Medicare enrollees comes from 2 sources: increased life expectancy and the fact that baby boomers are approaching the Medicare eligibility age. With respect to longer life expectancy, the rates of TKR among older Medicare beneficiaries (>80 years of age) did not change much, while larger 'incoming' cohorts may contribute to increase in utilization, but [by] no more than...about 10%."

Dr. Cram also suggested that the rise in primary joint replacement during the last 20 years may be followed by an increase in revision procedures during the next 15 years as those implants wear out.

"Revisions are more expensive, complicated, and risky," Dr. Cram said. "Another concern is that there seems to be an increase in infections among the revision arthroplasty cases. That warrants watching, particularly with the rise in antibiotic-resistant organisms."

Dr. Losina added, "While this study portrayed a large amount of historic data, most of the data are confirmatory to other previous studies. Furthermore, as more and more TKRs are performed in persons younger than 65 years of age, currently as much as 40% of all TKRs performed in [the United States], we have to be careful about generalization of Medicare data to all TKR cases. As more and more TKRs are being done, the issue of optimization of the timing of TKR and identifying factors related to suboptimal outcomes remain critical unanswered questions related to delivery of TKR in [the United States]."

In an accompanying editorial, James Slover, MD, and Joseph D. Zuckerman, MD, from the Hospital for Joint Diseases of New York University Langone Medical Center, New York City, write that Dr. Cram and colleagues might be looking at only the tip of the iceberg.

"By 2030, the demand for TKR in the United States is projected to be as high as 3.48 million procedures annually," Dr. Slover and Dr. Zuckerman write. "Cram et al address only Medicare beneficiaries, but the number of younger individuals (and those without Medicare) undergoing knee replacement is also expected to continue to increase. This is particularly true, considering the development of newer arthroplasty procedures used to treat degenerative arthritis in younger patients.... These projections will make TKR a key driver of health care cost, which make this procedure worthy of careful consideration."

The study was funded in part by grants from the National Heart Lung and Blood Institute and from the National Institute on Aging. Dr. Cram has disclosed that he is supported by an award from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and by the Department of Veterans Affairs and has received consulting fees from the Consumers Union and Vanguard Health Inc. One coauthor has received research funding from the Agency for Healthcare Research and Quality (AHRQ), Synthes USA, the American Geriatrics Society, the John Hartford Foundation, and the AO Research Foundation. One coauthor receives institutional research funding from the AHRQ, the US Food and Drug Administration, the National Institute on Aging, Takeda Pharmaceuticals, and Savient Pharmaceuticals; is a consultant for Takeda, Novartis, Savient, URL, and Ardea; has received travel grants from Allergan, Wyeth, Amgen, and Takeda; and has received speaker honoraria from Abbott. Dr. Zuckerman reported earning royalties for designing a shoulder arthroplasty system. The other authors, Dr. Slover, and Dr. Losina have disclosed no relevant financial relationships.

JAMA. 2012;308:1227-1236, 1266-1268. Article full text, Editorial extract

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