Influence of sacral morphology in developmental spondylolisthesis

Study Design. A radiographic study was conducted to investigate sacral morphology in a children and adolescent population with developmental L5-S1 spondylolisthesis. Objective. To determine the relationship between sacral morphology and developmental L5-S1 spondylolisthesis. Summary and Background Data. The morphology of the adult sacrum has been recently shown to be abnormal in low grade spondylolisthesis. However, sacral morphology has never been evaluated in a pediatric population where remodeling and secondary changes are less pronounced. It remains unknown if these changes in sacral morphology are primary or secondary in developmental L5-S1 spondylolisthesis. Methods. The lateral standing radiographs of 131 subjects, aged 6 to 20 years old with developmental L5-S1 spondylolisthesis (91 low grade and 40 high grade) were analyzed with a dedicated software allowing to measure the following parameters, which were analyzed for each subject by the same individual and compared to a cohort of 120 subjects without any spinal pathology with similar age and sex distribution: the sacral table index (STI), sacral table angle (STA), sacral kyphosis (SK), S1 superior angle, S2 inferior angle, and grade of spondylolisthesis. Student t test was used to compare the parameters between the groups. Results. This study demonstrated that STA is significantly smaller (P < 0.01) in children and adolescents with L5-S1 spondylolisthesis compared to a similar control group. Furthermore, STA is significantly smaller in high grade spondylolisthesis when compared to subjects with low grade. There is also a significant difference in segmental sacral morphology (S1 and S2 anatomy) in the spondylolisthesis group. Increasing sacral kyphosis is also found to be significantly associated with spondylolisthesis. Conclusion. The sagittal sacral morphology is a constant anatomic variable specific to each individual and unaffected by the position of the patient in space. The anatomy of the sacrum in children and adolescents with L5-S1 spondylolisthesis is particular and different from a control group. This study suggests that sacral anatomy may have a direct influence on the progression of spondylolisthesis; a lower STA and higher sacral kyphosis may be 2 factors predisposing to vertebral slip in developmental spondylolisthesis.