Hidden Blood Loss in Full-Endoscopic Lumbar Decompression Compared with Biportal Endoscopic and Open Microscopic Surgery for Single-Segment Lumbar Stenosis

Background/Objectives: Accurate estimation of intraoperative blood loss in endoscopic spine surgery remains challenging because of continuous saline irrigation and blood infiltration into surrounding soft tissues and potential dead spaces. Hidden blood loss (HBL), resulting from extravasation into tissue compartments or hemolysis, may substantially increase total blood loss (TBL) and contribute to postoperative bleeding-related complications. This study aimed to compare HBL in full-endoscopic unilateral laminotomy with bilateral decompression (FE-ULBD) with that in biportal endoscopic ULBD (BE-ULBD) and open microscopic ULBD (OM-ULBD). Methods: A retrospective analysis was conducted of patients who underwent single-level FE-ULBD, BE-ULBD, or OM-ULBD for lumbar spinal stenosis (LSS) at a single institution. Data on perioperative characteristics, laboratory parameters, perioperative blood loss (TBL, HBL, and visible blood loss), and clinical outcomes were collected and compared. Univariate linear regression analyses were performed to identify factors associated with HBL in the FE-ULBD group. Results: A total of 93 patients were included, comprising 34 in the FE-ULBD group, 32 in the BE-ULBD group, and 27 in the OM-ULBD group. The FE-ULBD group demonstrated significantly lower TBL than both the BE-ULBD and OM-ULBD groups (493.20 ± 183.46 vs. 675.97 ± 192.02 vs. 822.94 ± 424.11 mL, p = 0.001 and p = 0.002, respectively). HBL in the FE-ULBD group was significantly lower than in the BE-ULBD group (390.48 [268.32–506.91] vs. 513.29 [437.96–633.36] mL, p = 0.012) and was numerically lower than in the OM-ULBD group without statistical significance (390.48 [268.32–506.91] vs. 516.38 [316.41–710.68] mL, p = 0.081). Male sex was the only variable significantly associated with increased HBL in the FE-ULBD group. Conclusions: FE-ULBD showed significantly lower TBL than BE-ULBD and OM-ULBD, and lower HBL than BE-ULBD. FE-ULBD may represent a feasible surgical option for single-level LSS, with the potential advantage of reduced perioperative blood loss while maintaining comparable clinical outcomes.