The number of total knee replacement surgeries more than tripled between 1993 and 2009, while the number of total hip replacements doubled during the same time period. A study in the June Journal of Bone and Joint Surgery found that an increase in the prevalence of obesity in the United States accounted for 95 percent of the higher demand for knee replacements, with younger patients affected at a greater rate.
Previous studies have found a strong link between a higher body mass index and knee osteoarthritis. The effects of weight on hip osteoarthritis were less clear. In this study, researchers reviewed at least 10 years of national data (through 2009) on TKR and THR volume, length of hospital stay, in-hospital mortality, and orthopaedic workforce trends.
“We found that this differential growth rate in total knee replacement procedures could not be attributed to changes in physician or hospital payments, length of hospital stays, in-hospital death rates, or surgical workforce characteristics,” said lead study author Peter B. Derman, M.D., M.B.A., an orthopaedic surgery resident at the Hospital for Special Surgery in New York. “Because excess body weight appears to be more damaging to the knee than to the hip, the increasing prevalence of overweight and obesity may explain the growing demand for knee replacements over hip replacements.
“If rates of overweight and obesity continue to climb, we should expect further acceleration in the number of knee replacements performed annually in the U.S. with a more modest increase in hip replacement volumes,” said Dr. Derman. “This knowledge can inform future policy decisions regarding health care funding and surgical workforce training as well as guide allocation of preventative health resources.”