Thoracic Lordosis, Especially in Males, Increases Blood Loss in Adolescent Idiopathic Scoliosis

Background: Intraoperative blood loss during posterior spinal fusion for adolescent idiopathic scoliosis (AIS) has been reportedly associated with multiple factors. This study aims to investigate the effect of thoracic kyphosis on blood loss in AIS spinal fusion. Methods: Patients with AIS who underwent posterior-only procedures for Lenke I and II type curves were identified. All included patients had intraoperative tranexamic acid. Difference in estimated blood loss per blood volume (EBL/BV) was identified between hypokyphotic curves (-), normal curves (N), and hyperkyphotic curves (+) classified based on Lenke sagittal modifier. Regression analysis was then performed with EBL/BV as dependent variable. Independent variables included radiographically measured T5-T12 kyphosis and calculated 3D T5-T12 kyphosis in addition to sex, body mass index (BMI), operative time, number of fused vertebrae, number of Ponte osteotomy levels, and main thoracic coronal curve. Results: In total, 837 patients were included. For female patients: EBL/BV was significantly higher for (-) (18%) compared with (N) (16%) and (+) (14%). A total of 29 female patients had T5-T12 <= 0 (-15 to 0 degree). EBL/BV was not significantly higher than patients with T5-T12>0 degree (18%+/- 9% vs. 16%+/- 11%; P=0.212). For male patients: EBL/BV was significantly higher in (-) (23%) compared with (+) (16%). In total, 14 male patients had T5-T12 <= 0 (-13 to 0) degree. EBL/BV was significantly higher than patients with T5-T12>0 degree (32%+/- 18% vs. 18%+/- 13%; P=0.015). Significant factors in predicting EBL/BV were sex, BMI, number of fused levels, and both 2D and 3D T5-T12 kyphosis. Male sex as well as every fused-level predicted an increase in EBL/BV similar to 2%. Every 10-unit decrease in BMI predicted an increase in EBL/BV of 7%. Every 10-degree decrease in 2D or 3D T5-T12 kyphosis predicted an increase in EBL/BV similar to 1%. The impact of the number of Ponte osteotomy levels was not significant. Conclusions: This study supports the role of sagittal thoracic alignment in affecting EBL/BV in AIS surgery. Male patients with severe thoracic lordosis (T5-T12 <= 0 degree) are the highest risk group for intraoperative bleeding. These findings are helpful in predicting the intraoperative blood loss for patients with AIS undergoing posterior spinal fusion. In addition to sex and number of fused levels, decreased thoracic kyphosis is associated with increased blood loss.