Lumbar Level Significantly Influences Postoperative Global Sagittal Balance Following Pedicle Subtraction Osteotomy

Study Design: Retrospective cohort study. Objectives: The current evidence regarding how level of lumbar pedicle subtraction osteotomy (PSO) influences correction of sagittal alignment is limited. This study sought to investigate the relationship of lumbar level and segmental angular change (SAC) of PSO with the magnitude of global sagittal alignment correction. Methods: This study retrospectively evaluated 53 consecutive patients with adult spinal deformity who underwent lumbar PSO at a single institution. Radiographs were evaluated to quantify the effect of PSO on lumbar lordosis (LL), thoracic kyphosis (TK), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), T1-spinopelvic inclination (T1SPI), T1-pelvic alignment (TPA), and sagittal vertical axis (SVA). Results: Significant correlations were found between PSO SAC and the postoperative increase in LL (r = 0.316, P = .021) and PT (r = 0.352, P = .010), and a decrease in TPA (r = -0.324, P = .018). PSO level significantly correlated with change in T1SPI (r = -0.305, P = .026) and SVA (r = -0.406, P = .002), with more caudal PSO corresponding to a greater correction in sagittal balance. On multivariate analysis, more caudal PSO level independently predicted a greater reduction in T1SPI (beta = -3.138, P = .009) and SVA (beta = -29.030, P = .001), while larger PSO SAC (beta = -0.375, P = .045) and a greater number of fusion levels (beta = -1.427, P = .036) predicted a greater reduction in TPA. Conclusion: This study identified a gain of approximately 3 degrees and 3 cm of correction for each level of PSO more caudal to L1. Additionally, a larger PSO SAC predicted greater improvement in TPA. While further investigation of these relationships is warranted, these findings may help guide preoperative PSO level selection.