Body Mass Index Modifies the Effect of Hemovac Drainage on Blood Loss After Total Knee Arthroplasty.

OBJECTIVES: The role of Hemovac drainage after TKA remains uncertain in the tranexamic acid (TXA) era, particularly across patient subgroups. This study investigated whether body mass index (BMI) modifies the association between drainage use and blood loss in patients undergoing TKA. METHODS: This retrospective cohort study compared 201 TKA patients divided into a drain group (n = 101) and a non-drain group (n = 100). All procedures incorporated standardized intravenous and intra-articular administration of tranexamic acid. Primary outcomes included hemoglobin (Hb), hematocrit (Hct), erythrocyte count, and estimated blood loss (EBL). Secondary outcomes were hospital stay duration, knee range of motion, and complications. Between-group comparisons were performed using independent-samples t-tests and chi-squared tests, and multiple linear regression assessed the interaction between BMI and drain use on EBL. RESULTS: No significant between-group differences were observed in Hb, Hct, or erythrocyte count at baseline or on postoperative Day 1. In patients with BMI ≥ 25 kg/m2, EBL was significantly lower in the drain group compared to the non-drain group (p = 0.044). Regression analysis revealed a significant interaction between drain use and BMI (p = 0.013). Patients without drains showed an increase in EBL with BMI, whereas the drain group demonstrated a relatively flat relationship. Secondary outcomes were comparable between groups. CONCLUSION: Hemovac drains were associated with modestly lower EBL in patients with BMI ≥ 25 kg/m2 undergoing TKA. No differences in clinical outcomes were observed. These findings suggest that the effect of drainage may vary across patient subgroups and support a more individualized approach.