Risk factors for perioperative hidden blood loss after one-segment posterior circumferential decompression surgery on thoracic ossification of the posterior longitudinal ligament: a finding of the double-layer sign on CT

Background Hidden blood loss (HBL) is of increasing interest to spine surgeons. This retrospective study aimed to evaluate perioperative HBL and its risk factors in patients undergoing one-segment posterior circumferential decompression surgery on thoracic ossification of the posterior longitudinal ligament (T-OPLL). Method We retrospectively studied 112 patients diagnosed with T-OPLL following posterior circumferential decompression surgery from August 2015 to June 2020. Patient demographics, blood loss-related parameters, surgery-related data and imaging parameters were extracted. Postoperative complications were also recorded. Pearson or Spearman correlation analysis was used to investigate the correlation between patient demographics and HBL. Multivariate linear regression analysis was performed to determine the independent risk factors associated with HBL. Results Forty-five men and 67 women were involved in this research, with an average age of 56.4 ± 10.2 years. The mean HBL was 459.6 ± 275.4 ml, accounting for 56.5% of the total blood loss. Multiple linear regression analysis showed that double-layer sign ( P = 0.000), ossification occupancy ratio (OOR) > 60% ( P = 0.030), age ( P = 0.010), hematocrit (Hct) loss ( P = 0.034), and postoperative Hct ( P = 0.016) were independent risk factors for HBL. However, OPLL morphology ( P = 0.319), operation time ( P = 0.587), hemoglobin (Hb) loss ( P = 0.644), and postoperative Hb ( P = 0.952) were not significantly different from HBL. Conclusion A high proportion of HBL was found after posterior circumferential decompression surgery on T-OPLL during the perioperative period, which should not be overlooked. Double-layer sign, OOR > 60%, age, Hct loss and postoperative Hct are independent risk factors for HBL.