The Effect of Reduction and Instrumentation of Spondylolisthesis on Spinopelvic Sagittal Alignment

Background: Reduction of severe spondylolisthesis is controversial. Publications have emphasized the techniques of reduction and associated complications, but there is little knowledge about the effect of reduction on the sagittal balance of the spine and pelvis in the postoperative patient. This study evaluated the effect of surgical reduction and instrumented fusion of spondylolisthesis on the pelvic anatomy and spinopelvic sagittal balance. Methods: This is a retrospective study of 26 adolescents (mean age, 13.1 +/- 3.3 years) who had partial surgical reduction and posterior instrumented fusion L4 to sacrum to treat high-grade spondylolisthesis. All patients had radiographs that allowed measurement of sagittal spinopelvic parameters at preoperative., postoperative, and at a minimum of 2 years' follow-up (mean, 7.5 +/- 5.4 years). A 10-degree reduction in lumbosacral angle and/or 10% reduction of anterior listhesis confirmed the reduction. Radiographic measurements were statistically compared to determine correlations between reduction and sagittal balance. Results: Pelvic incidence increased in 5 (24%) of 21 patients who had posterior instrumented fusion. Pelvic version improved in patients with unbalanced spondylolisthesis as evidenced by reduction of pelvic tilt or/and increased sacral slope. Mean pelvic tilt improved by 5.7 degrees (95% confidence interval, 1.5-9.8 degrees), and mean sacral slope improved by 11.4 degrees (95% confidence interval, 5.9-17.0 degrees). Two of 6 patients with a balanced spondylolisthesis developed a retroverted sacrum at follow-up. There was poor correlation between the amount of surgical reduction (improvement in L5 slip and lumbosacral angle) and the changes in pelvic version. Clinical Relevance: Partial reduction and instrumented fusion of spondylolisthesis may lead to increased pelvic incidence due to sacroiliac joint motion or sacral remodeling. In unbalanced spondylolisthesis, pelvic sagittal balanced improved in 75% of patients but did not correlate to the amount of reduction of spondylolisthesis. Other factors, such as achievement of solid arthrodesis, may be more important than reduction of spondylolisthesis in determining spinopelvic sagittal balance. Level of Evidence: IV-case series.