Surgical strategy for revisional lumbar pedicle subtraction osteotomy to correct fixed sagittal imbalance: The effect of the osteotomy level and iliac screw fixation

Background: More caudal osteotomy is believed to lead to greater sagittal correction; however, the osteotomy level and whether or not to use iliac screw fixation (ISF) are topics of on-going debate. The aim of this study was to compare clinical and radiographic outcomes after revisional lumbar pedicle subtraction osteotomy (PSO) for fixed sagittal imbalance (FSI) according to the osteotomy level and ISF. Methods: All consecutive patients who underwent revisional PSO (at L3 or L4) for FSI in a single institute from July 2006 to January 2014 were investigated retrospectively. Thirty-eight patients with at least 2-year follow-up were finally included. Clinical outcomes including the visual analogue scale (VAS) and Oswestry Disability Index (ODI) were investigated. Radiographic spinopelvic parameters were analyzed according to the level of PSO, the degree of correction, and the use of ISF. Results: The mean number of fused segments after PSO was 6.6 ± 1.8. Sagittal vertical axis (SVA) was restored after the surgery (12, 2.5, and 5.2 cm at preoperative, postoperative, and the last follow-up, respectively). PSO was performed at L3 in 16 patients and at L4 in 22 patients. The osteotomy level was not associated with any changes of spinopelvic parameters (pelvic tilt [PT] or lumbar lordosis) or sagittal alignment (T1-pelvic angle [TPA] or SVA). However, better TPA restoration was achieved with more osteotomy resection angle (P = 0.031). ISF group showed significant improvement in postoperative pelvic orientation (PT and ratio of PT to pelvic incidence) which was maintained until the last follow-up. Conclusions: Although postoperative sagittal alignment was different in FSI patients according to the osteotomy level, pelvic orientation improved in ISF group. Also, the degree of correction showed significant associations with sagittal alignment. When performing revisional PSO for FSI, spine surgeon should carefully consider how to correct rather than where to do the osteotomy, and the role of ISF.