Characteristics of hidden blood loss following hybrid total knee arthroplasty

Hidden blood loss (HBL) unrecognized by the usual practice of assessing intraoperative loss and postoperative drainage comprises a considerable proportion of total blood loss (TBL) during primary total knee arthroplasty (TKA). However, HBL has not been adequately investigated in hybrid TKA (uncemented femur, cemented tibia). The purpose of this study was to clarify the amount and influential factors of HBL in hybrid TKA.A consecutive series of 151 knees in 137 patients with knee osteoarthritis who underwent hybrid TKA were retrospectively evaluated. We examined the correlations between HBL and various factors of concern for their effects on TBL, including age, sex, body weight (BW), body height, body mass index, operation time, tourniquet time, and visible blood loss (VBL) in three periods (intraoperative: VBL1; until 3 h postoperatively: VBL2; from 3 h to 1 day postoperatively: VBL3).Median (interquartile range) HBL and TBL were 528 (388, 711) mL and 725 (582, 926) mL, respectively. HBL relative to TBL (H/T) was 73%. There were weak correlations between HBL and BW (r = 0.249, p = 0.002) and between HBL and VBL3 (r = -0.261, p = 0.001). Multivariate analyses confirmed a positive correlation between HBL and BW (β = 0.296, p < 0.001) and a negative correlation between HBL and VBL3 (β = -0.270, p < 0.001).Hybrid TKA showed comparable values of HBL and H/T to those reported for cemented TKA. Therefore, management strategies for HBL in hybrid TKA can follow the same protocols used for cemented TKA. High BW and low VBL3 may be predictors of postoperative HBL in hybrid TKA.