Study design: Retrospective study of the importance of sacral and sacro-pelvic morphology in developmental L5-S1 spondylolisthesis.
Objectives: To determine and compare the importance of sacral and sacro-pelvic morphology in developmental L5-S1 spondylolisthesis. Recent studies have shown abnormalities in sacral and sacro-pelvic morphology in spondylolisthesis. However, it is still unclear if sacral and sacro-pelvic morphology are correlated and if they are equally important in the progression of spondylolisthesis.
Methods: Lateral radiographs of 120 controls and 131 subjects with developmental L5-S1 spondylolisthesis were analyzed. Sacral table angle (STA) and pelvic incidence (PI) were compared using Student t tests. The relationship between STA and PI was assessed separately in the control and spondylolisthesis groups using Pearson's coefficients. The proportion of subjects with high PI but average STA was compared to the proportion of subjects with low STA but average PI using χ (2) tests.
Results: STA was significantly lower and PI was significantly higher in the spondylolisthesis group. STA was statistically related to PI in both control (r = -0.43) and spondylolisthesis (r = -0.57) groups. In the spondylolisthesis group, STA (r = -0.45) and PI (r = 0.35) were significantly related to slip percentage. STA remained statistically related to slip when controlling for PI. A significantly greater proportion of subjects in the spondylolisthesis group had average STA and high PI, rather than average PI and low STA.
Conclusion: The significant relationship between PI and STA validates that geometrically sacral morphology depends on sacro-pelvic morphology. This study failed to demonstrate a clear predominant role of either STA or PI in the presence of spondylolisthesis.