Approximately 600,000 total knee arthroplasties (TKA) are performed each year in the United States, costing about $15,000 per procedure. “TKA has been shown to markedly improve health-related quality of life and functional status and is highly cost-effective,” says Peter Cram, MD, MBA. “The number of TKA procedures in the U.S. has been increasing in recent years due to the surgery’s effectiveness for reducing pain and improving function for our aging population.” This trend, however, may further strain the government, insurers, and patients struggling with the ever-increasing healthcare spending.

Despite the important role of TKA in healthcare utilization and costs, few analyses have evaluated recent trends in using these surgeries as well as outcomes associated with them. In an issue of JAMA, Dr. Cram and colleagues had a study published that evaluated longitudinal trends in primary and revision TKA among Medicare enrollees. The analysis involved more than 3 million Medicare patients who underwent primary TKA and over 300,000 who underwent revision TKA. A secondary objective was to examine patient and hospital factors that increased risk for hospital readmission.

Significant Increases in TKA

The number of Americans undergoing primary and revision TKA jumped substantially from 1991 to 2010, according to findings from Dr. Cram’s study. The volume of initial knee replacements and revisions more than doubled during the study period. Among Medicare beneficiaries, annual primary TKA volume increased by 161.5%, rising from 93,230 to 243,802. Per capita utilization increased by 99.2%, increasing from 31.2 procedures per 10,000 Medicare enrollees in 1991 to 62.1 procedures per 10,000 in 2010. Revision TKA volume increased by 105.9%, rising from 9,650 to 19,871. Per capita utilization increased 59.4%, going from 3.2 procedures per 10,000 Medicare enrollees in 1991 to 5.1 procedures per 10,000 in 2010 (Figure).

“Better success rates and the aging of the baby boomer generation that wants to remain physically active as they get older and have increased the popularity of TKA,” says Dr. Cram. “This growth is likely driven by a combination of factors, including an expansion of the types of patients who can benefit from TKA. This includes not only our aging population, but also patients with certain conditions that predispose them to osteoarthritis, most notably obesity and diabetes.”

Readmissions for TKA Also Rising

Over the past 20 years, Dr. Cram and colleagues observed a marked decline in hospital length of stay (LOS) from 7.9 days from 1991 to 1994 to 3.5 days from 2007 to 2010 (Table). Rates of adverse outcomes resulting in readmission remained stable between 1991 and 2010 for primary TKA, but rates of all-cause 30-day readmission increased from 4.2% to 5.0%. For revision TKA, the decrease in hospital LOS was accompanied by an increase in all-cause 30-day readmission, which rose from 6.1% to 8.9%. The decreased LOS was also linked to an increase in readmission for wound infection, which rose from 1.4% to 3.0%.

“The rise in readmissions appears to be associated with the decline in hospital LOS,” explains Dr. Cram. “For revision TKA, reducing the hospital LOS may lead to less vigilance for early signs of superficial wound infections during the postoperative period. This can result in higher rates of serious infectious complications. The increase in infection rates associated with revision TKA warrants close attention.”

Assessing the Implications on Knee Implants

Knee implants can be expected to last anywhere from 15 to 20 years, meaning many patients who undergo surgery in their 50s and 60s will live long enough to require a second operation. As the field continues to advance, newer implants may last longer than the earlier models. “We hope that these new implants are more durable and are associated with fewer complications thanks to improved surgical techniques,” Dr. Cram says. “Time will tell, but in the meantime it’s likely that the rapid increase in primary TKA will eventually lead to greater demand for revision procedures as implants wear over time. This possibility would have significant clinical and economic implications.”

Dr. Cram says that there is an inherent tradeoff between shorter hospital LOS, increased need for post-acute care, and higher readmission rates in TKA. “The key is for clinicians to determine the candidates who are most appropriate for these procedures and who can be optimally managed with shorter LOS to avoid future readmissions,” he says. “Clinical guidelines must be followed because the potential savings associated with TKA are significant in terms of productivity and the costs of ongoing care.”

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