[The correlation analysis between sacral slope and the morphological characteristics of intervertebral disc, paraspinal muscle and pedicle in patients with degenerative lumbar spondylolisthesis]

Abstract

Objective: To analyzed the correlation between the sacral slope (SS) and the slip degree of vertebral body, the morphological parameters of intervertebral disc, paraspinal muscle and pedicle in patient with degenerative lumbar spondylolisthesis (DLS). Methods: A retrospective cohort study was conducted. One hundred and forty patients with L_4-5 degenerative spondylolisthesis who visited the Department of Orthopedics, the Affiliated Hospital of Southwest Medical University from July 2018 to October 2022 were included. There were 32 males and 108 females, with an age of (62.6±10.0) years (range: 42 to 87 years) and the body mass index was (23.8±2.8) kg/m²(range: 14.7 to 28.7 kg/m²). General information and imaging data (lumbar X-ray, CT three-dimensional reconstruction, MRI images) of the patients were collected. SS and the slip degree (SD) of the L₄ vertebral body were measured on lateral lumbar radiographs. Based on Roussouly classification, 140 patients with DLS were divided into a low SS group (SS<35°), a medium SS group (35°≤SS<45°), and a high SS group (SS≥45°). The morphological parameters of the L₄ pedicle of the patient were measured on the lumbar CT three-dimensional reconstruction images, including pedicle length (PL), pedicle width (PW), pedicle screw trajectory length (PSTL), pedicle camber angle(PCA) and pedicle height (PH). The morphological parameters of the paraspinal muscles (psoas major, multifidus and erector spinae) were measured on MRI images, including total cross-sectional muscle area (TCSA), functional cross-sectional muscle area (FCSA), and the ratio of functional cross-sectional muscle area (FCSA/TCSA) was calculated. The degree of degeneration of the L_4-5 disc was assessed on MRI images. The slip degree, morphological parameters of the pedicle, intervertebral disc, and paraspinal muscles among the groups were compared and their correlation was analyzed. The comparison of quantitative data was conducted using one-way analysis of variance, and the post hoc analysis for pairwise comparisons among groups was performed using the least significant difference method. The comparison of unordered categorical data was carried out using the χ² test, and the comparison of ordered categorical data was conducted using the Kruskal-Wallis rank sum test. Pearson correlation analysis was used to test the correlation. Results: Among the 140 patients, there were 70 in the low SS group, 48 in the medium SS group, and 22 in the high SS group. The SD and PL of the low SS group were the lowest ((18.6±4.2)%, (14.0±1.0) mm), those of the medium SS group were slightly higher ((21.0±3.6)%, (15.7±0.9) mm), and those of the high SS group were the highest ((23.7±2.8)%, (16.2±0.7) mm), with statistically significant differences among the groups (all P<0.01). The PW, PH and PCA of the low SS group were the highest ((11.0±1.1) mm, (11.0±1.0) mm, 22.9°±1.1°), those of the medium SS group were slightly lower ((10.2±1.1) mm, (10.4±0.9) mm, 21.6°±1.3°), and those of the high SS group were the lowest ((9.6±0.9) mm, (9.4±0.7) mm, 18.7°±1.5°), with statistically significant differences among the groups (all P<0.05). The FSCA/TCSA of the psoas major, erector spinae and multifidus muscles in the low SS group were the highest ((93.1±4.0)% and (77.6±6.4) %), next were those in the medium SS group ((90.9±3.5)% and (74.9±6.1)%), and those in the high SS group were the lowest ((88.6±4.4)% and (71.2±7.4) %), with statistically significant differences among the different groups (all P<0.05). Pearson correlation analysis showed that SS was positively correlated with SD(r=0.557,P<0.01); SS was negatively correlated with the FSCA/TCSA of the paraspinal muscles (psoas major, erector spinae+multifidus) (r=-0.393,-0.394,both P<0.01); SS was positively correlated with PL and PSTL (r=0.706,P<0.01;r=0.264, P<0.01), and negatively correlated with PW, PCA and PH (r=-0.469,-0.669,-0.549, all P<0.01). The Pfirrmann grade of intervertebral disc degeneration in the low SS group was better than that in the medium SS group and the high SS group(H=23.128,P<0.01). Conclusions: In DLS patients, as SS increases, the SD of the L₄ vertebral body gradually increases, the proportion of paraspinal muscle functional area gradually decreases, the degree of intervertebral disc degeneration gradually worsens, the pedicle gradually becomes slender, and the pedicle camber angle gradually decreases. There is a correlation between SS and the degree of vertebral slippage, as well as morphological parameters of pedicle, intervertebral disc, and paraspinal muscles.