Thoracic Kyphosis Reduction as the Important Compensatory Mechanism in Low-Grade Spondylolisthesis: A Correlation...

When spondylolisthesis occurs, several compensatory mechanisms are induced not only within the spine itself but also in the pelvis. We investigated the process of spine shift from a decompensated state to compensated malalignment. This study aimed to evaluate the sagittal plane malalignment and explore the major compensatory mechanism for maintaining sagittal balance in low-grade spondylolisthesis.

This was a retrospective study of 60 patients with low-grade spondylolisthesis and 30 volunteers without radiographical abnormalities of the spine and pelvis conducted between June 2016 and June 2017. Based on the Meyerding classification, 90 participants were divided into 3 groups: group A (n = 30), normal volunteers; group B (n = 30), patients with Meyerding grade I spondylolisthesis; and group C (n = 30), patients with Meyerding grade II spondylolisthesis. Correlation and partial correlation analyses between the slipping grade and spino-pelvic parameters were performed. One-way analysis of variance (ANOVA) was conducted to compare the effects of thoracic kyphosis (TK) and pelvic incidence (PI) in individuals with normal conditions as well as those with Meyerding grades I and II spondylolisthesis.

A significant correlation was found between the grade of slipping and max thoracic kyphosis (maxTK) (r = -0.344, P = 0.002), PI (r = 0.601, P < 0.001), sacrum slope (SS) (r = 0.354, P = 0.001), and pelvic tilt (PT) (r = 0.431, P < 0.001), whereas no significant correlations were observed between the grade of slipping and age, bone mass index, sagittal vertical axis (SVA), and max lumbar lordosis. In partial correction, no significant correlations were observed in the grade of slipping and PT (r = 0.002, P = 0.988) and SS (r = -0.002, P = 0.988). A one-way ANOVA was conducted to compare TK and PI between the groups, and indicated there were significant effect at the P < 0.05 level for the 3 conditions (P = 0.007, P < 0.001).

Greater PI may lead to the development and progression of spondylolisthesis. In patients with low-grade spondylolisthesis, decreased TK acts as an important compensatory way to maintain sagittal balance, relative to the normal population.