Several reports have examined the pathophysiology of degenerative spondylolisthesis. However, very little work is known on the influence of sagittal spinal balance in its pathogenesis. The purpose of this study was to present a descriptive analysis of pelvic and spinal parameters of sagittal balance in a cohort of 70 patients treated for degenerative spondylolisthesis and to compare findings with those established in a population of 250 volunteers. The goal was to deduce pathophysiological hypotheses and identify therapeutic implications.

Seventy patients were included in this study. The following variables were noted: pelvic incidence and tilt, sacral slope, lumbar lordosis, thoracic kyphosis, T9 sagittal offset, and S1-S2 angle. These variables were measured on digitalized lateral views of the spine using previously validated software (SpineView™). Univariate analysis of the values obtained was first performed to identify the variable distributions. Multivariate analysis was then carried out to study the relationships between these variables and to better define perturbations of spinal sagittal balance in the anteroposterior plane. The findings were compared with those obtained in a control population.

One of the essential characteristics of the cohort of patients with degenerative spondylolisthesis was the high pelvic incidence (62.6° versus 54.7° in the control population). The most significant determinants of T9 sagittal offset (which reflects sagittal balance) were pelvic tilt, pelvic incidence, lumbar lordosis, and L4-S1 local lordosis. One-third of our patients presented posterior offset due to exaggerated thoracic kyphosis. The high pelvic incidence, via hyperlordosis and increased pelvic tilt, could be one of the factors favoring degenerative disease of the spinal unit.

This investigation enabled us to better describe sagittal balance in patients with degenerative spondylolisthesis and to propose hypotheses concerning the underlying mechanism of progressive degeneration. We emphasize the diversity of spinal balance in these patients and the different therapeutic implications.