Obesity increases length of stay and direct medical costs in total hip arthroplasty

Abstract

Background: The number of obese patients undergoing THA is increasing. Previous studies have shown that obesity is associated with an increased likelihood of complications after THA, but there is little information regarding the impact of obesity on medical resource use and direct medical costs in THA.

Questions/purposes: We sought to examine the relationship between obesity, length of stay, and direct medical costs in a large cohort of patients undergoing THAs.

Methods: The study included 8973 patients who had undergone 6410 primary and 2563 revision THAs at a large US medical center between January 1, 2000, and September 31, 2008. Patients with bilateral procedures within 90 days after index admission and patients with acute trauma were excluded. Data regarding clinical, surgical characteristics, and complications were obtained from the original medical records and the institutional joint registry. Patients were classified into eight groups based on their BMI at the time of surgery. Direct medical costs were calculated by using standardized, inflation-adjusted costs for services and procedures billed during hospitalization and the 90-day window. Study end points were hospital length of stay, direct medical costs during hospitalization, and the 90-day window. End points were compared across the eight BMI categories in multivariable risk-adjusted linear regression models.

Results: Mean length of stay and the direct medical costs were lowest for patients with a BMI of 25 to 35 kg/m(2). Increasing BMI was associated with longer hospital stays and costs. Every five-unit increase in BMI beyond 30 kg/m(2) was associated with approximately USD $500 higher hospital costs and USD $900 higher 90-day costs in primary THA (p = 0.0001), which corresponded to 5% higher costs. The cost increase associated with BMI was greater in the revision THA cohort where every five-unit increase in BMI beyond 30 kg/m(2) was associated with approximately USD $800 higher hospital costs and USD $1500 higher 90-day costs. These estimates remained unchanged after adjusting for comorbidities or complications.

Conclusions: Obesity is associated with longer hospital stays and higher costs in THA. The significant effect of obesity on costs persists even among patients without comorbidities but the increased costs associated with obesity may be balanced by the potential benefits of THA in the obese. Increasing prevalence of obesity likely contributes to the increasing financial burden of THA worldwide.

Level of evidence: Level IV, economic and decision analyses. See the Instructions for Authors for a complete description of levels of evidence.

Fig. 1

The trends in mean BMI and percentage of obese patients (BMI ≥ 30 kg/m²) undergoing THAs between 2000 and 2008 are shown.

Fig. 2

The mean (median) lengths of stay by BMI categories among patients undergoing THA are shown.

Fig. 3

The mean (median) hospitalization costs by BMI categories among patients undergoing THA are shown in 2010 US dollars.

Fig. 4

The mean (median) 90-day costs by BMI categories among patients undergoing THAs are shown in 2010 US dollars.