Obesity Linked to Higher Costs for TKA Patients

Comorbidities play key role in increasing costs

Jennie McKee

Obesity is a real problem in the United States. According to recent national data, more than one third of U.S. adults were considered obese in 2009–2010. As obesity rates continue to rise, orthopaedists are performing more total knee arthroplasty (TKA) procedures on younger, heavier patients.

Research presented yesterday by Hilal Maradit-Kremers, MD, MSc, of the Mayo Clinic, Rochester, Minn., found that patients with high body mass indexes (BMIs) had higher costs and longer hospital stays. Although the overall complication rates were similar in all BMI categories, complications from infections were significantly more common in obese patients.

“In analyses restricted to patients with no comorbidities or complications, the association with BMI was still significant, suggesting that the effect of obesity on costs was independent of obesity-related comorbid conditions,” noted Dr. Maradit-Kremers. Every 5 unit increase in BMI beyond 30 kg/m2 was associated with approximately $250 to $300 in higher hospitalization costs for primary TKA and $600 to $650 in higher hospitalization costs for revision TKA.

Reviewing the data
The study evaluated 8,129 patients who underwent 6,475 primary and 1,654 revision TKA procedures between Jan. 1, 2000, and Sept. 31, 2008, at Mayo Clinic. Patients who underwent bilateral procedures during the same hospitalization or within 90 days after discharge were excluded.

The researchers accessed medical records and the institution’s joint registry for data on study participants’ clinical and surgical characteristics and complications, such as infections, thrombovascular events, instability, and fractures. They classified patients into the following eight categories, depending on the patients’ BMIs at the time ofsurgery:

BMI less than 18.5
BMI of 18.5 but less than 25
BMI of 25 but less than 30
BMI of 30 but less than 35
BMI of 35 but less than 40
BMI of 40 but less than 45
BMI of 45 but less than 50
BMI of 50 or more

Patient BMIs ranged from 15 to 73. Among primary TKA patients, the proportion of obese patients (defined as having a BMI ≥30 kg/m2) increased from 49 percent to 59 percent during the study period. Among revision TKA patients, the proportion of obese patients increased from 51 percent to 62 percent.

Length of hospital stay and direct medical costs during hospitalization and the 90-day global period were compared across the eight BMI categories, using unadjusted and multivariable risk-adjusted linear regression models.

Measuring the effect of BMI
Mean length of stay and costs were lowest for patients in the normal to overweight range.

“We observed a J-shaped relationship wherein the length of stay and costs were lowest for patients who had normal BMI or were slightly overweight, and highest for patients at extreme ends of the BMI spectrum,” stated Dr. Maradit-Kremers.

After adjusting for factors such as age, sex, and type of surgery, the investigators found that every 5 unit increase in BMI beyond 30 kg/m2 was associated with an additional $250 to $300 in hospitalization costs and an additional $500 in 90-day costs in primary TKA. The cost increase associated with BMI was higher in revision TKA procedures, where every 5 unit increase in BMI beyond 30 kg/m2 was associated with an additional $600 to $650 in hospitalization costs and an additional $900 in 90-day costs. When analyses were restricted to patients with no significant comorbidities or complications, these associations remained significant.

Overall, said Dr. Maradit-Kremers, the study’s findings “suggest that increasing prevalence of obesity in the TKA population likely contributes to the financial burden of TKA, at least during hospitalization and the early period after surgery.”

Dr. Maradit-Kremers’ coauthors on Scientific Paper 349, “The Effect of Obesity on Direct Medical Costs in Total Knee Arthroplasty,” are Sue L. Visscher, PhD; Walter K. Kremers, PhD; James Naessens, MPH; David G. Lewallen, MD.

Disclosure information: Drs. Maradit-Kremers, Visscher, and Kremers—no conflicts. Mr. Naessens—Journal of Primary Care & Community Health. Dr. Lewallen—Zimmer; Pipeline Biomedical Holdings; Clinical Orthopaedics and Related Research; American Joint Replacement Registry; Hip Society; Orthopaedic Research and Education Foundation.

2013 Annual Meeting News
Tuesday through Friday, February 19 – 23, 2013.
http://www.aaos.org/news/acadnews/2013/AAOS13_3_22.asp