PURPOSE:
The development of isthmic spondylolisthesis is influenced by forces across the lumbosacral region of the spine. Pelvic incidence is a radiographic parameter that has been shown to be an independent parameter that influences both sagittal spinal balance and pelvic orientation. Our hypothesis then is that there is a positive correlation between pelvic incidence and spondylolisthesis.

STUDY DESIGN:
A radiographic analysis of cases with spondylolisthesis.

OBJECTIVES:
To try to assess the correlation between pelvic incidence in both low-grade and high-grade spondylolisthesis in both a pediatric and an adult population.

SUMMARY OF BACKGROUND DATA:
The concept of pelvic incidence has been introduced into the literature. Its exact association with spondylolisthesis has not yet been clarified.

METHODS:
Forty patients with spondylolisthesis were identified and divided into two groups: low-grade (Meyerding I-II) and high-grade (Meyerding III and higher). Radiographic parameters measured included lumbar sagittal alignment (T12-S1), sacral inclination, slip angle, and pelvic incidence. The spondylolisthesis was classified according to the Meyerding-Newman classifications and the slip angle. Radiographic measurements were also done in two control groups; there were 20 pediatric and 20 adult controls (mean age 11.8 years and 60.0 years, respectively). Unpaired t test analysis and Pearson correlation analysis were then done.

RESULTS:
Mean pelvic incidence was 47.4 degrees in the pediatric control group, 57 degrees in the adult control group, 68.5 degrees in the low-grade isthmic spondylolisthesis group, and 79.0 degrees in the high-grade isthmic spondylolisthesis group. Pelvic incidence was found to be significantly higher in the high- and low-grade spondylolisthesis groups compared with both control groups (P = 0.0001). Pelvic incidence was significantly higher in the high-grade isthmic spondylolisthesis group than in the low-grade isthmic spondylolisthesis group (P = 0.007). A significant correlation existed between pelvic incidence and Meyerding-Newman scores (P = 0.03).

CONCLUSIONS:
Pelvic incidence was significantly higher in patients with low- and high-grade isthmic spondylolisthesis as compared with controls and had significant correlation with the Meyerding-Newman grades (P = 0.03).



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