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Obesity is associated with longer hospital stays and higher costs in total knee replacement patients, according to a new study. The condition is independent of whether or not the patient has an obesity-related disease or condition. 

The study reviewed BMI, comorbidities, complications, outcomes and cost of care of 8,129 patients who had undergone 6,475 primary TKRs and 1,654 revision TKRs at major medical center between Jan 1 2000 and Sept. 30, 2008. 

Researchers found that the most common patient comorbidities were hypertension and diabetes. 

Length of stay and direct medical costs were also found to be lowest for patients with BMI values in the normal to overweight range. 

The study noted that every 5-unit increase in BMI beyond 30 kg/m² was associated with a mean hospital stay that was .11 days longer for patients undergoing primary TKR and .06 days longer for patients undergoing revision TKR. The observation was well founded for patients with and without comorbidities. 

"The higher costs associated with obesity are believed to be largely due to managing comorbid medical conditions linked to obesity, such as diabetes," said lead study author Hilal Maradit-Kremers, MD, an associate professor of epidemiology at Mayo Clinic in Rochester, Minn, in the press release. And yet in this study, "even in the absence of comorbidities, patients with obesity had longer stays and higher hospital costs."

"The bottom line is that obesity is increasingly common among patients undergoing joint replacement, which creates a myriad of technical and medical challenges, and likely contributes to the financial burden of the surgery," said senior author David G. Lewallen, MD, an orthopaedic surgeon, also from Mayo Clinic, in the press release. 

The study is published in the Journal of Bone and Joint Surgery(JBJS).