Impact of body mass on hospital resource use in total hip arthroplasty

Objective: To determine the impact of BMI on post-operative outcomes and resource utilization following elective total hip arthroplasty (THA). Design: A retrospective cohort analysis on all primary elective THA patients between 1996 and 2004. Primary outcomes investigated using regression analyses included length of stay (LOS) and costs (US dollars). Setting: Mayo Clinic Rochester, a tertiary care centre. Subjects: Patients were stratified by pre-operative BMI as normal (18.5-24.9 kg/m²), overweight (25.0-29.9 kg/m²), obese (30.0-34.9 kg/m²) and morbidly obese (≥35.0 kg/m ²). Of 5642 patients, 1362 (24.1 %) patients had a normal BMI, 2146 (38.0 %) were overweight, 1342 (23.8 %) were obese and 792 (14.0 %) were morbidly obese. Results: Adjusted LOS was similar among normal (4.99 d), overweight (5.00 d), obese (5.02 d) and morbidly obese (5.17 d) patients (P = 0.20). Adjusted overall episode costs were no different (P = 0.23) between the groups of normal ($17 211), overweight ($17 462), obese ($17 195) and morbidly obese ($17 655) patients. Overall operative and anaesthesia costs were higher in the morbidly obese group ($5688) than in normal ($5553), overweight ($5549) and obese ($5593) patients (P = 0.03). Operating room costs were higher in morbidly obese patients ($3418) than in normal ($3276), overweight ($3291) and obese ($3340) patients (P < 0.001). Post-operative costs were no different (P = 0.30). Blood bank costs differed (P = 0.002) and were lower in the morbidly obese group ($180) compared with the other patient groups (P < 0.05). Other differences in costs were not significant. Morbidly obese patients were more likely to be transferred to a nursing home (24.1 %) than normal (18.4 %), overweight (17.9 %) or obese (16.0 %) patients (P = 0.001 each). There were no differences in the composite endpoint of 30 d mortality, re-admissions, re-operations or intensive care unit utilization. Conclusions: BMI in patients undergoing primary elective THA did not impact LOS or overall institutional acute care costs, despite higher operative costs in morbidly obese patients. Obesity does not increase resource utilization for elective THA.