Obese patients tend to stay in the have a higher risk of requiring knee replacements and have a longer hospital stays when undergoing the procedure.

More than half of all total knee replacement (TKR) patients have a body mass index that puts them in the obesity range, an American Academy of Orthopaedic Surgeons news release reported.  

Obesity is linked to health problems such as "diabetes, hypertension, osteoarthritis," the news release reported.

Past research has suggested obese patients tend to have longer hospital stays, but the researcher is inconclusive as to whether these longer stays are a product of obesity or comorbidity (obesity-related diseases).

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

The most common comorbidities were diabetes and hypertension.

For every five-unit increase in BMI the risk of higher hospital costs increased. In 2010 the numbers were about "$250 to $300 for patients undergoing TKR and $600 to $650 for patients undergoing a revision joint replacement," the news release reported.

For every five-unit increase in BMI there was also a mean hospital stay that was .11 days longer for patients undergoing TKR and .06 days longer in those going through revision TKR. This data remained consistent for both patients with and without comorbidities.

"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, said in the news release.