Sacral and lumbar-pelvic morphology in high-grade spondylolisthesis.

Numerous authors have stressed the importance of posterior arch, vertebral bodies, and intervertebral disk dysplastic changes in lumbosacral spondylolisthesis. An extensive morphologic analysis was conducted of the lumbosacral junction in a series of 100 consecutive patients presenting with severe lumbosacral spondylolisthesis. Statistical correlations were found between the pelvic incidence, sacral slope, and pelvic tilt, as found in healthy volunteers. A statistical relationship exists between the lumbosacral kyphosis and pelvic parameters that explains the global sagittal "balance" of this pathological posture. A well-defined morphological criterion, the "S1 index," strongly correlated with the severity and stiffness of lumbosacral spondylolisthesis.