Classification of High Grade Spondylolisthesis

Purpose: To analyze the sagittal spinopelvic alignment in patients with high-grade spondylolisthesis and identify sub groups that may require reduction to restore sagittal balance.

Methods: 133 subjects, mean age 17, with high-grade spondylolisthesis were identified from a multiple center data base containing standing lateral radiographs of patients with developmental spondylolysis/spondylolisthesis. The films were digitized and custom software determined the sagittal alignment of the spine and pelvis. K-means cluster analysis was performed to identify two natural groups based on the pelvic tilt and sacral slope. Correlations were determined for lumbosacral angle (LSA), lumbar lordosis (LL), pelvic incidence (PI), L5 incidence (L5I), and thoracic kyphosis (TK) and groups were compared by paired T test.

Results: Cluster analysis identified two distinct groups: reverted pelvis with vertical sacrum had high PT (mean 36.5) / low SS (mean 40.3) and a balanced pelvic version group with low PT/ high SS (mean 21.3 /59.9). The retroverted pelvis with vertical sacrum group had significantly greater PI, L5I, and LSA and less TK than the balanced pelvic group.

n PI L5I LSA LL TK
Retroverted pelvis 71 76.8 77.1 29.0 75.2 33.7
Balanced pelvis 62 81.2 52.5 9.4 73.4 42.0
P value .038 <.001.

Conclusion: Analysis of sagittal alignment of patient with high grade spondylolisthesis revealed 2 distinct groups. Those with a high PT/low SS had a retroverted pelvis with vertical sacrum and highly significant greater LSA and L5I, and significant less TK than the group with balanced pelvic version. Significance: High-grade spondylolisthesis occurs in patients with two distinct orientations of sagittal sacral alignment. The mechanical strain on the spinopelvic junction will differ in each group. Treatment strategies for high-grade spondylolisthesis may differ for each group; reduction techniques might be considered in the retroverted pelvis group of patients with high-grade spondylolisthesis.