Postoperative changes in pelvic parameters and sagittal balance in adult isthmic spondylolisthesis

Background: Correction of deformity in adult isthmic spondylolisthesis can affect the pelvic parameters and sagittal balance. Objective: To evaluate the correlation with the amount of deformity correction and the subsequent change in pelvic parameters after surgical correction of adult isthmic spondylolisthesis and to determine which deformity parameter most affects the postoperative restoration of spinopelvic sagittal alignment. Methods: Fifty-eight patients with 1-level isthmic spondylolisthesis were included. Their average age was 55 years (range, 24-76 years). All patients underwent operation by posterior lumbar interbody fusion and posterior instrumentation. The pre- and postoperative sacral slope, pelvic tilt, lumbar lordosis (LL), and sagittal balance were measured, and then the correlation between these parameters and deformity parameters such as slip degree, slip angle, and height of the intervertebral disc (HOD) was evaluated. Results: The slip degree, slip angle, and HOD were significantly recovered after surgery. Pelvic parameters and sagittal balance changed subsequently. Sacral slope was increased by 4.4 degrees, and pelvic tilt was decreased by 4.4 degrees. LL was increased by 5.2 degrees and sagittal balance was displaced 5.6 mm posteriorly. Only the restoration of the HOD showed a significant correlation with the change in LL (r = 0.305, P = .02) and sagittal balance (r = 0.377, P = .004). Conclusion: Surgical correction of adult isthmic spondylolisthesis with posterior lumbar interbody fusion and posterior instrumentation resulted in improvement of sacral slope, pelvic tilt, LL, and sagittal balance. Only restoration of the HOD was significantly correlated with improvement of LL and sagittal balance. Therefore we presume it is important to restore the HOD in surgical correction of adult isthmic spondylolisthesis.