Classification of high-grade spondylolistheses based on pelvic version and spine balance - Possible rationale for reduction

Study Design. Retrospective review of a radiographic database of high-grade spondylolisthesis patients in comparison with asymptomatic controls. Objective. To analyze the sagittal spinopelvic alignment in high-grade spondylolisthesis patients and identify subgroups that may require reduction to restore sagittal balance. Summary of Background Data. High-grade spondylolisthesis is associated with an abnormally high pelvic incidence (PI); however, the spatial orientation of the pelvis, determined by sacral slope (SS) and pelvic tilt ( PT), is not known. We hypothesized that sagittal spinal alignment would vary with the pelvic orientation. Methods. Digitized sagittal radiographs of 133 high-grade spondylolisthesis patients ( mean age, 17 years) were measured to determined sagittal alignment. K-means cluster analysis identified 2 groups based on the PT and SS, which were compared by paired t test. Comparisons were made to asymptomatic controls matched for PI. Results. High-grade spondylolisthesis patients had a mean PI of 78.9 +/- 12.1. Cluster analysis identified a retroverted, unbalanced pelvis group with high PT (36.5 +/- 8.0)/low SS (40.3 +/- 9.0) and a balanced pelvic group with low PT ( mean 21.3 +/- 8.2)/high SS (59.9 +/- 11.2). The retroverted pelvis group had significantly greater L5 incidence and lumbosacral angle with less thoracic kyphosis than the balanced pelvic group. A total of 83% of controls had a "balanced pelvis" based on the categorization by SS and PT. Conclusion. Analysis of sagittal alignment of high-grade spondylolisthesis patients revealed distinct groups termed "balanced" and "unbalanced" pelvis. The PT and SS were similar in controls and balanced pelvis patients. Unbalanced pelvis patients had a sagittal spinal alignment that differed from the balanced pelvis and control groups. Treatment strategies for high-grade spondylolisthesis should reflect the different mechanical strain on the spinopelvic junction in each group; reduction techniques might be considered in patients with an unbalanced pelvis high-grade spondylolisthesis.