Correlation of Pelvic Incidence with Low and High-Grade Isthmic Spondylolisthesis

Washington University, Orthopaedic Surgery, St. Louis, MO, USA

PURPOSE: The development of isthmic spondylolisthesis is influenced by forces across the lumbosacral region of the spine that are greatly affected by the orientation of the pelvis. Pelvic incidence is a radiographic parameter originally described by Legaye and Duval-Beaupere 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.

METHODS: 40 patients with spondylolisthesis were identified and divided into 2 groups, low-grade (Meyerding I-II) and high-grade (Meyerding III and higher) spondylolisthesis. Their standing radiographs were then examined for several radiographic parameters including lumbar sagittal alignment (T12-S1), segmental sagittal alignment, sacral inclination (SI), L3 tilt, and pelvic incidence (PI). The spondylolisthesis was classified according to the Meyerding classification, the Neumann classification, and the slip angle (SA). The same radiographic measurements were then made for 40 patients with no history of spine problems; there were 20 pediatric controls (mean age 11.8 yr.) and 20 adult controls (mean age 60.0 yr). Unpaired t-test analysis was undertaken to look for significant variation between groups. Pearson correlations were analyzed for correlation of pelvic incidence and lumbar lordosis, slip angle, Meyerding score and Neumann score.

*p=0.001
**p=0.0001

Pelvic incidence was found to be significantly higher in the high-grade spondylolisthesis group compared to the pediatric control group and the adult control group (p= 0.0001). The low-grade spondylolisthesis group also had significantly higher pelvic incidence values than the adult or pediatric control groups (p=0.001). The pelvic incidence was significantly higher in the high-grade IS group than in the low-grade IS group (p=0.007). A significant correlation existed between pelvic incidence and Meyerding/Neumann scores (p=0.03).

CONCLUSIONS: Pelvic incidence increased significantly in patients with low and high-grade isthmic spondylolisthesis as compared to controls and had significant correlation with the Meyerding and Neumann grades (p=0.03). Pelvic incidence may be a predictive factor for both high and low-grade spondylolisthesis with significant correlation and should be considered a factor in treatment as well as in assessment for risk of progression.