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Spondylolisthesis, Pelvic Incidence, and Spinopelvic Balance: A Correlation Study

Study Design. A retrospective study of the sagittal alignment in developmental spondylolisthesis. Objectives. To investigate the role of pelvic anatomy and its effect on the global balance of the trunk in developmental spondylolisthesis. Summary of Background Data. Pelvic incidence (PI) is a fundamental anatomic parameter that is specific and constant for each individual, and independent of the three-dimensional orientation of the pelvis. Recent studies have suggested an association between a high PI and patients with isthmic spondylolisthesis. Methods. The lateral standing radiographs of the spine and pelvis of 214 subjects with developmental L5–S1 spondylolisthesis were analyzed with a dedicated software allowing the calculation of the following parameters: pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), thoracic kyphosis (TK), and grade of spondylolisthesis. All measurements were done by the same individual and compared to those of a cohort of 160 normal subjects. Student’s tests were used to compare the parameters between the curve types and Pearson’s correlation coefficients were used to investigate the association between all parameters (&agr; = 0.01). Results. PI, SS, PT, and LL are significantly greater (P < 0.01) in subjects with spondylolisthesis, while TK is significantly decreased. PI has a direct linear correlation (0.41–0.65) with SS, PT, and LL. Furthermore, the differences between the two populations increase in a direct linear fashion as the severity of the spondylolisthesis increases. Conclusions. Since PI is a constant anatomic pelvic variable specific to each individual and strongly determines SS, PT, and LL, which are position-dependent variables, this study suggests that pelvic anatomy has a direct influence on the development of a spondylolisthesis. Study participants with an increased pelvic incidence appear to be at higher risk of presenting a spondylolisthesis, and an increased PI may be an important factor predisposing to progression in developmental spondylolisthesis.