Obesity and population growth can’t account for increase in utilization

From 1997 to 2007, the number of total knee arthroplasty (TKA) procedures performed annually in the United States doubled, with much of the increase taking place in younger patients, according to a study presented at the 2011 AAOS Annual Meeting.

The rising number of TKA cases has been linked to a growing population and a rising national obesity epidemic. To verify this, the research team drew data from the National Inpatient Sample—a large all-payer inpatient care database overseen by the U.S. Agency for Healthcare Research and Quality. They divided patients into four age groups—18–44 years, 45–64 years, 65–84 years, and 85 years or older—and compared use of TKA in each age group against growth in population and obesity over time.

A shifting landscape
Given the association between obesity and osteoarthritis, rising obesity has been proposed as a factor in increased TKA use. Population growth, especially among the elderly, may also lead to an increasing number of joint replacements. But could these two factors account for most of the increase in TKA utilization between 1997 and 2007?

During the study period, the overall U.S. adult population grew 1.13-fold and the prevalence of obesity grew 1.12-fold. But the number of TKAs performed more than doubled—from 264,311 in 1997 to 549,707 in 2007. When researchers examined population growth, obesity rates, and number of TKAs performed by age group, they found the greatest growth in TKAs among those younger than age 65 (Table 1).

What is driving the increase?
“Even assuming that the increases in obesity and population size were completely independent, they would only account for a 24.4 percent growth in procedures over the decade of the study, or just 22.6 percent of the approximately 100 percent increase in the number of TKAs performed,” said author Elena Losina, PhD, director of the Orthopaedic and Arthritis Center for Outcomes Research at Brigham and Women’s Hospital in Boston.

Given that, it is unlikely that the rapid expansion of TKA utilization can be fully explained by increases in population and obesity prevalence.

Other factors that may be driving the increase in TKA include an increasingly active population and expanded indications for surgery among a younger patient population.

Previous studies have linked sport-related knee injuries and increased physical activity in younger people to an increase in early-onset osteoarthritis. Therefore, active lifestyle increases may help explain why rising numbers of younger patients are receiving TKAs.

In addition, because data have shown that younger and healthier patients have better post-TKA outcomes, the indications for performing surgery have been expanded to include these patients.

Limitations of the study include its retrospective nature, which may not be indicative of future trends. In addition, the population, utilization, and obesity data were all drawn from different sources, which compromised somewhat the ability to compare changes.

Dr. Losina’s coauthors include Thomas S. Thornhill, MD; Benjamin N. Rome; John J. Wright, MD; and Jeffrey N. Katz, MD, MSc. Read the abstract of “Can We Explain the Dramatic Rise in TKR Rates in the U.S. by Population Size and the Obesity Epidemic?”

Disclosure information: Drs. Losina and Katz—no conflicts. Dr. Thornhill—DePuy and Conformis; Dr. Wright—DePuy; Mr. Rome—no disclosure. The research was supported in part by grants from the National Institutes of Health, National Institute for Arthritis and Musculoskeletal and Skin Diseases.

Bottom line

• This retrospective analysis attempted to determine whether the increases in TKAs could be explained solely by population growth and obesity prevalence.
• Increases in population and obesity account for only about 25 percent of the increase in TKAs.
• The number of TKAs being performed among individuals younger than age 65 years has grown much faster than the number of TKAs being performed among individuals age 65 years or older.
• Expanded indications for TKAs among younger patient populations and more active lifestyles leading to an increase in early-onset osteoarthritis may be additional factors.

Peter Pollack is a staff writer for AAOS Now. He can be reached at ppollack@aaos.org