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

<bold>Study Design: </bold>Retrospective review of a radiographic database of high-grade spondylolisthesis patients in comparison with asymptomatic controls. <bold>Objective: </bold>To analyze the sagittal spinopelvic alignment in high-grade spondylolisthesis patients and identify subgroups that may require reduction to restore sagittal balance. <bold>Summary Of Background Data: </bold>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. <bold>Methods: </bold>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. <bold>Results: </bold>High-grade spondylolisthesis patients had a mean PI of 78.9 degrees +/- 12.1 degrees . Cluster analysis identified a retroverted, unbalanced pelvis group with high PT (36.5 degrees +/- 8.0 degrees )/low SS (40.3 degrees +/- 9.0 degrees ) and a balanced pelvic group with low PT (mean 21.3 degrees +/- 8.2 degrees )/high SS (59.9 degrees +/- 11.2 degrees ). 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. <bold>Conclusion: </bold>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. [ABSTRACT FROM AUTHOR]