Correlation of Sacropelvic Geometry with Disc Degeneration in Spondylolytic Cadaver Specimens

Study Design: An anatomic study of sacral inclination, pelvic incidence, pelvic lordosis, and disc degeneration in cadaveric lumbar spines.

Objective: To evaluate the relationship between sacropelvic parameters and disc degeneration in subjects with bilateral spondylolysis at L5.

Summary Of Background Data: L5-S1 disc degeneration is greater in patients with spondylolytic defects (L5-S1) than with an intact pars interarticularis secondary to the instability caused by spondylolysis. Sacral inclination, pelvic incidence, and pelvic lordosis affect sagittal balance and axial forces on the L5-S1 disc.

Methods: An observational study was performed on 120 cadaveric specimens with spondylolysis (L5-S1) identified of 3100 total cadaveric specimens. Nine specimens were excluded because of incomplete or degraded skeletal elements; 10 were excluded for having unilateral defects only. The specimens were evaluated for sacral inclination, pelvic incidence, and pelvic lordosis. Disc degeneration and facet arthrosis at L4-L5 and L5-S1 were measured by the classification of Eubanks et al. Linear regression analyses were then used to determine the relationship between sacropelvic parameters and degeneration at the L5-S1 segment, correcting for confounding factors such as age, sex, and race.

Results: Linear regression demonstrated a significant association between sacral inclination and disc degeneration at L5-S1 (P = 0.018). Specimens were then divided into two groups, those in the highest quarter of pelvic incidence, and the remainder. Spearman rank correlation demonstrated a significant association between disc degeneration at L5-S1 and the highest quarter of pelvic incidence (P = 0.017). Increasing pelvic lordosis was also associated with an increase in facet arthrosis at L4-L5 (P = 0.006).

Conclusion: The findings of this study show a relationship between the sacropelvic geometry and the degree of L5-S1 disc degeneration as well as L4-L5 facet degeneration in spondylolytic specimens. This relationship may prove useful in predicting the course of disc degeneration in patients with spondylolysis.