Spotlight on Research 2012

September 2012

Obesity and Population Increases Not Solely Responsible for Knee Replacement Upswing

A dramatic upsurge in the number of total knee replacement (TKR) surgeries in the U.S. is attributable to more than increases in obesity and population size alone, according to researchers at Bostonís Brigham and Womenís Hospital. Their recent study of 1999-2008 data shows a doubling of surgeries performed in that decade, an increase disproportionate to those in obesity and population growth. Other factors at work—particularly in younger TKR patients—may include changes in the onset and progression of knee osteoarthritis (OA), changes in indicators for surgery, and an increase in knee injuries, say the scientists. The research, supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a component of the NIH, was described in The Journal of Bone and Joint Surgery.

Senior study author Elena Losina, Ph.D., and her team used data from the National Center for Health Statistics, National Health and Nutrition Examination Survey (NHANES) and the Nationwide Inpatient Sample (the largest database of inpatient care in America) to compare the number of TKR surgeries during 1999-2008 with accompanying rates of population aging and obesity. Three age groups were examined: 18-44, 45-64, and 65 and over. During that time,

  • The population increased by 1 percent for the 18-44 group; 29 percent for ages 45-64; and 12 percent for those over 65. Overall, the population over 18 years of age rose 11 percent.
  • Obesity increases were estimated at 17 percent for 18-44; 32 percent for 45-64; and 14 percent for the plus 65 group. For the overall adult population, the number of obese Americans increased 23 percent.

By contrast, TKR increases were 119 percent (18-44); 218 percent (45-64); and 97 percent (65 and over), for an average 134 percent increase for the decade.

The disparities between the exploding surgery rates and lower population and obesity increases suggest that other factors may be at work, including earlier onset, more rapid progression of OA, as well as changed clinical indicators for TKR.

The public health impact of these findings could be significant, according to Dr. Losina. "In addition to the financial costs, surgeries like TKR are accompanied by demands on surgeons, nurses, rehabilitation specialists and many other health care professionals, not to mention the facilities that support them," she says. "Understanding the entire range of factors involved in this increase could help us improve treatments and offer informed recommendations to reduce the burden of knee surgery."

The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the U.S. Department of Health and Human Servicesí National Institutes of Health (NIH), is to support research into the causes, treatment, and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about NIAMS, call the information clearinghouse at (301) 495-4484 or (877) 22-NIAMS (free call) or visit the NIAMS website at http://www.niams.nih.gov.

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Losina E, Thornhill TS, Rome BN, Wright J, Katz JN. The dramatic increase in total knee replacement utilization rates in the United States cannot be fully explained by growth in population size and the obesity epidemic. J Bone Joint Surg Am. 2012 Feb 1; 94(3):201-7. PMID: 22298051.