Introduction: Surgical outcome of Adult Spinal Deformity has been shown to be strongly affected by post‐op global sagittal alignment. To achieve appropriate alignment numerous surgical maneuvers may be utilized including the Pedicle Subtraction Osteotomy (PSO) technique. The purpose of this study is to investigate radiographic parameters tied to successful and unsuccessful post‐op alignment in the setting of PSO surgery.
Methods: Retrospective, consecutive, multi‐center series of 105 patients who underwent a lumbar PSO for marked sagittal mal‐alignment (mean pre‐op SVA=143mm). Pre and post‐op full length standing xrays were analyzed to identify changes in lumbar lordosis [LL], thoracic kyphosis [TK], global sagittal balance (SVA), and pelvic parameters (pelvic incidence [PI] and pelvic tilt [PT]). The cohort was divided into two groups according to the post‐op SVA: ‘successful realignment’ (SVA<5cm, n=62), ‘failed realignment’ (SVA>10cm, n=20). Independent t‐test analysis was used to identify differences in pre‐op patient profiles and/or amount of deformity correction.
Results: Comparisons between the two groups demonstrated similar pre‐op LL and TK. The ‘failed realignment’ group had larger pre‐op SVA (21 vs. 10cm, p<0.001), larger pelvic incidence (64° vs. 54°, p=0.001) and larger pelvic tilt (37° vs. 31°, p=0.003). PSO application resulted in identical focal resection (23°) and lordosis change (+29°) for the two groups. In post‐op, the ‘failed realignment group’ had greater SVA and PT. Multi‐variate analysis revealed that pre‐op SVA and PT, as well as the change in regional alignment was tied to global alignment outcome.
Conclusion: PSO technique can be used to obtain significant sagittal re‐alignment, although sub‐optimal results may still occur. This study demonstrates 2 subgroups of patients with similar PSO resections, changes in LL, TK, SVA and PT, although one group reached an acceptable post‐op SVA and the other a large unacceptable one. As per the multi‐variate analysis, ‘unacceptable’ post‐op alignment could have been predicted pre‐operatively, and would have required larger local resections and/or a larger regional. In patients with large pre‐op SVA/ PT, the standard PSO technique alone may be insufficient to obtain proper sagittal realignment.