As orthopedic surgeons search for objective measures that predict total joint arthroplasty (TJA) outcomes, body mass index may aid in risk stratification. The purpose of this study was to compare in-hospital TJA outcomes and resource consumption amongst underweight (body mass index ≤19 kg/m2) and morbidly obese patients (≥40 kg/m2).
Discharge data from 2006 to 2012 National Inpatient Sample were used for this study. A total of 1503 total hip arthroplasty (THA) and 956 total knee arthroplasty (TKA) patients were divided into 2 cohorts, underweight (≤19 kg/m2) and morbidly obese (≥40 kg/m2). Patients were matched by gender and 27 comorbidities by use of Elixhauser Comorbidity Index. Patients were compared for 13 in-hospital postoperative complications, length of stay, total hospital charge, and disposition. Multivariate analyses were generated by SAS software. Significance was assigned at P value <.05.
Underweight patients undergoing primary TJA had higher risk for developing postoperative anemia compared with morbidly obese patients (TKA: odds ratio [OR], 3.1; 95% CI, 2.3-4.1; THA: OR, 1.8; 95% CI, 1.5-2.3). Underweight THA candidates displayed greater risk for deep venous thrombosis (75.36% vs 24.64%; OR, 3.1; 95% CI, 1.1-8.4). Underweight TJA patients were charged more (TKA: USD 51,368.90 vs USD 40,128.80, P = .001, THA: USD 57,451.8 vs USD 42,776.9, P < .001) compared to the morbidly obese patients. Length of stay was significantly longer for underweight THA patients (4.6 days vs 3.5 days, P = .008) compared to morbidly obese counterparts.
Our results indicate underweight, compared to morbidly obese, TJA patients are at a greater risk for postoperative anemia and consume more resources.