Radiological assessment of lumbosacral dystrophic changes in high-grade spondylolisthesis.

OBJECTIVE: To analyse radiographic correlates for the clinical status of patients and the deformation reducibility of high-grade lumbosacral spondylolisthesis. We also clarify the clinical and radiographic correlates of a new parameter for S1 dystrophy, the "S1 index". DESIGN AND PATIENTS: One hundred cases of high-grade isthmic lumbosacral spondylolisthesis were reviewed. We noted the dystrophic changes in the cranial sacral endplate, and the caudal endplate of L5. The severity of the spondylolisthesis was evaluated by measuring the lumbosacral kyphosis. The clinical status and the deformation reducibility (dependent on the stiffness of the deformation) were compared with these dystrophic patterns, the sagittal slope of S1 and S2 endplates and a sacral morphological marker, the S1 index.
RESULTS: Lumbosacral kyphosis was less severe in cases with dystrophic changes of the posterior cranial edge of S1 and/or of the posterior caudal edge of L5 but its reducibility was worse. These patients were more functionally impaired. We describe and analyse this situation as a partial lumbosacral disc failure responsible for the less severe L5 slipping. The S1 index was strongly correlated with the grade of slipping, the lumbosacral kyphosis and its reducibility. We noted the same configuration among patients with a smaller S1 index, i.e. vertical S1 and S2 vertebral bodies associated with more severe but more reducible lumbosacral kyphosis.
CONCLUSION: Analysing specific criteria, we think it is possible to note progressive dystrophic changes according to the natural history of lumbosacral spondylolisthesis. We think that repeated measurements of these morphological parameters in patients diagnosed with a low-grade lumbosacral spondylolisthesis could be helpful in the early detection of evolving lumbosacral kyphosis and L5 slipping.