THURSDAY, July 29 (HealthDay News) -- After correcting for the natural weight gain expected with aging, many patients experience a decrease in weight and body mass index (BMI) after total knee or total hip replacement, according to research published in the June 1 issue of Orthopedics.

Kelly Stets, M.D., of the Mount Sinai Medical Center in New York City, and colleagues conducted a retrospective study of 196 patients (average age at surgery, 67.56 years) who had undergone total knee or total hip replacement from 2005 to 2007 to examine whether these patients had a significant change in BMI or body weight after surgery. The researchers noted that previous studies on the subject had not corrected their results based on the natural yearly positive BMI change in North Americans aged 29 to 73. The researchers in the present study did correct for this factor.

With a mean follow-up time of 20 months, 17.3 percent of the study subjects had a clinically significant (5 percent or more) weight loss and a drop in BMI when the researchers did not correct for natural weight gain with aging. This proportion increased to 19.9 percent when the researchers corrected for natural weight gain with aging. A higher percentage of patients in the knee replacement group achieved a clinically significant corrected BMI decrease than in the hip replacement group (21.5 versus 16.9 percent). Those patients who had a BMI greater than 30 kg/m² prior to surgery were most likely to experience post-surgery corrected weight loss.

"A prosthetic joint is not expected to be curative of obesity, which may have been founded in years of poor dietary habits and sedentary lifestyle. However, these results are suggestive that the postoperative subjects have improved weight parameters when compared to the tendencies of the North American population. A multidisciplinary prospective trial that incorporates nutritional guidance and long term fitness goals after total joint arthroplasty may show more encouraging results," the authors write.

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