Gender of patients and level of osteotomy are predictive factors for blood loss in ankylosing spondylitis patients undergoing pedicle subtraction osteotomy.

This study is to investigate the predictive factors of blood loss in ankylosing spondylitis (AS) patients. Retrospective analysis was performed in patients with thoracolumbar kyphotic deformity secondary to ankylosing spondylitis who underwent PSO from 2008 through 2013. Patient's demographics, preoperative and postsurgical global kyphosis (GK) angle, preoperative hematologic tests and other factors related to PSO were analyzed. Multiple regression analysis was used to determine the predictive factors of intraoperative blood loss. A total of 67 AS patients including 61 males and 6 females were included in the study. These had an average age of 33.97 years (17-55 years) and an average preoperative height of 167.77 cm (124-182 cm). There were 55 patients undergoing one-level osteotomy and 12 patients undergoing two-level osteotomy. Preoperative and postoperative GK angles were 79.08° ± 24.11° and 35.68° ± 21.48°, respectively. The mean surgical correction rate was 56.62% ± 21.45%. The mean length of surgery was 404.25 ± 82.57 minutes, and the estimated intraoperative blood loss was 2899.25 ± 1444.54 ml. The average percentage of estimated blood loss (EBL)/estimated blood volume (EBV) was 69.98% ± 41.44% (range, 23.57%-248.52%). Multiple stepwise analysis identified male sex (P = 0.000), and two-level osteotomy (P = 0.016) to be predictive factors of increased EBL/EBV percentage in AS patients undergoing PSO for thoracolumbar kyphosis. Male and two-level osteotomy are the two most significant factors predicting increased EBL/EBV percentage in AS patients undergoing PSO for thoracolumbar kyphosis. These predictors can provide more adequate preoperative preparations.