The Impact of Type 2 Diabetes and Obesity on Hospital Length of Stay After Total Knee Arthroplasty: An HCUP Study

OBJECTIVE To evaluate the impact of concurrent type 2 diabetes and obesity on hospital length of stay following total knee arthroplasty at the national level. RESEARCH DESIGN AND METHODS This retrospective cohort study used the Healthcare Cost and Utilization Project (HCUP) National Inpatient Sample (2017–2021) to evaluate adults undergoing total knee arthroplasty. After excluding missing data, the sample totaled 474,715 patients. Groups were categorized as concurrent type 2 diabetes and obesity, obesity alone, type 2 diabetes alone, or neither condition. Multivariable linear regression was used to assess the association between metabolic status and length of stay, adjusting for age, sex, race, and socioeconomic quartile. Baseline medical complexity was adjusted using the Elixhauser comorbidity index, excluding diabetes and obesity. RESULTS Adjusted regression revealed an increased length of stay across groups: concurrent type 2 diabetes and obesity (β = 0.20 days; 95% CI = 0.17–0.22; P < 0.001), type 2 diabetes alone (β = 0.12 days; 95% CI 0.11–0.14; P < 0.001), and obesity alone (β = 0.02 days; 95% CI 0.01–0.04; P = 0.002). CONCLUSIONS Cumulative metabolic dysfunction significantly compounds inpatient resource use after primary total knee arthroplasty, with type 2 diabetes and obesity leading to extended stays. Notably, the effect of type 2 diabetes alone was approximately five times greater than that of obesity alone, demonstrating that it is the dominant driver of prolonged hospitalization. These findings suggest that cumulative metabolic dysfunction significantly impacts inpatient resource use, highlighting the value of increased preoperative metabolic optimization.