Difference and correlation analysis of spinal pelvic sagittal parameters and sacral parameters between two types of spondylolisthesis

Background　Previous studies have found correlations between sacral parameters and spinal-pelvic sagittal parameters, but there is limited research on the sacral morphology parameters in patients with different types of spondylolistheses. Objective　To analyze the characteristics and correlations of spinal pelvic sagittal parameters and sacral morphology parameters in patients with different types of spondylolistheses, and explore their roles in the mechanisms of different types of spondylolistheses. Methods　A retrospective analysis was conducted on the full-length standing spine radiographs of the patients with lumbar spondylolisthesis treated in the Department of Orthopedics of the First Medical Center of PLA General Hospital from January 2019 to December 2023, the healthy adults who visited for physical examination during the same period were selected as controls. Spinal pelvic sagittal parameters were measured, including thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sagittal vertical axis (SVA), and slip angle (SA). Sacral morphological parameters were measured, including S1-2 tilt (S1-2T), sacral kyphosis (SK), and the horizontal angle of S5Co1 (S5Co1HA). Independent sample t-tests was used to compare parameters between groups. Correlation analysis was performed between spinal pelvic sagittal parameters and sacral parameters within groups, and linear regression equations were obtained.Results　A total of 91 patients with spondylolisthesis were included in the study group, with a mean age of (61.45 ± 11.56) years. Among them, 57 patients had degenerative spondylolisthesis (26 males and 31 females, mean age of 65.49 ± 8.29 years), and 34 patients had isthmic spondylolisthesis (18 males and 16 females, mean age of 54.68 ± 13.13 years). The control group included 35 healthy adults (16 males and 19 females, mean age of 64.77 ± 10.47 years,). There was no statistical difference in gender distribution among the three groups (P＞0.05), while the difference in age distribution was significant (P＜0.01). In the degenerative spondylolisthesis group and the isthmic spondylolisthesis group, the TK (29.78°±13.71° and 30.56°±13.61° vs 38.94° ± 10.51°) was lower than those in the healthy control group, PI (54.06°±10.99° and 56.10°±10.76° vs 49.33°±8.92°) and PT (22.84°±8.68° and 21.45°±9.31° vs 12.32°±5.86°) were all higher than those in the healthy control group (P<0.05). In the degenerative spondylolisthesis group, the LL (40.42°±20.44° vs 49.25°±11.17°) and SS (31.42° ±10.59° vs 37.01° ±8.11° ) were lower than those in the healthy control group (P < 0.05). The SA in the degenerative spondylolisthesis group was significantly lower than that in the isthmic spondylolisthesis group (P < 0.05). The SK (57.23°±13.29° and 56.01°±11.69° vs 50.35°±9.77) in both the degenerative spondylolisthesis group and the isthmic spondylolisthesis group was higher than that in the healthy control group (P < 0.05), while the S5Co1HA (80.70°±9.68° and 81.45°±11.56° vs 94.45°±12.02°) was lower than that in the healthy control group (P < 0.05). The S1-2T (17.09° ±7.08° vs 13.15° ±9.08° ) in the degenerative spondylolisthesis group was higher than that in the isthmic spondylolisthesis group (P < 0.05). The multiple linear regression equation for the degenerative spondylolisthesis group was PI=0.383SK-0.753 (S1-2T) +44.989 (R=0.727), and the multiple linear regression equation for the isthmic spondylolisthesis group was PI=0.529SK-0.876 (S1-2T) +38.001 (R=0.815).Conclusion　This study demonstrates that patients with both degenerative and isthmic lumbar spondylolisthesis exhibit similar characteristic changes in sacral morphology, including a significantly increased sacral kyphosis angle and a markedly reduced S5Co1 inclination line horizontal angle. These characteristic alterations show significant correlations with spino-pelvic sagittal imbalance, with the combination of sacral kyphosis angle and S1-2 inclination angle effectively predicting pelvic incidence. The findings suggest that sacral morphological parameters can serve as important complementary indicators for assessing spino-pelvic balance in patients with lumbar spondylolisthesis, providing new anatomical basis for developing personalized treatment strategies in clinical practice.