1.1 Patient Case Selection
To perform this study, we obtained institutional review board approval from our ethics committee and informed signed consents were provided by all participating subjects. Database records of patients with DLS treated in our hospital were retrospectively reviewed between January 1, 2017, to June 30, 2020 (as our hospital had updated and used a new medical record system since January 1, 2017). Patients included in the study should be defined as L4/5 single-segment DLS with Meyerding classification of grade I-II, and were required to have complete imaging studies (including full-length spine radiographs, flexion and extension lumbar radiographs, lumbar computed tomography (CT) and three-dimensional reconstruction, and lumbar magnetic resonance (MR) images) and available clinical data (including demographic characteristics, chief complaint, neurological function, medical history, visual analogue scale (VAS) and Oswestry disability index (ODI)). Exclusion criteria were patients with multi-segment spondylolisthesis, previous surgery or trauma history, and combined with other spinal diseases including tumor, tuberculosis, infection, deformity, metabolic bone disease, etc. Finally, a total of 108 consecutive cases in accordance with the criteria were involved in the current study. According to the morphology of the intervertebral space on the standing radiographs, patients were divided into 1) kyphotic group, with larger anterior disc height; and 2) non-kyphotic group, with lower anterior disc height (Figure 1).[6,7]
1.2 Imaging Measurement and Assessment
A resident of our department who did not participate in the later statistics and analysis collected these cases from the database. 2 independent expert spine surgeons were selected to assess imaging studies and measure parameters separately as they were unaware of the identity of the patients and the treatment they received. IDC Cygnus Version 1.2 (DICOM image viewing software) was used to measure sagittal parameters as follows:
Spondylolisthetic parameters: 1) slip degree (SD), measured as the slipped distance of L4 divided by the length of L5 upper endplate; 2) anterior disc height (ADH), measured as the distance from L5 anterior upper corner to L4 lower endplate; 3) posterior disc height (PDH), measured as the distance from L4 posterior lower corner to L5 upper endplate; 4) slip angle (SA), defined as the angle between L4 lower endplate and L5 upper endplate; 5) slip angle motion (SAM), defined as the absolute value of subtraction between slip angles in radiograph (standing) and T2-weighted MR image (supine); and 6) slip degree motion (SDM), defined as the absolute value of subtraction between slip degrees in radiograph and T2-weighted MR image.[15,16]
Spino-pelvic parameters: 1) lumbar lordosis (LL), measured as the angle subtended between tangents of T12 lower endplate and S1 sacral endplate; 2) sacral slope (SS), measured as the angle subtended between tangent of S1 endplate and horizontal line; 3) pelvic tilt (PT), defined as the angle between the vertical and a line from the center of the femoral heads to the midpoint of the sacral endplate; 4) pelvic incidence (PI), defined as the angle subtended between a line perpendicular to the sacral plate at its midpoint and a line connecting this point to the axis of the femoral heads; 5) thoracic kyphosis (TK), defined as the angle between the perpendicular of T5 upper endplate and the perpendicular of T12 lower endplate; and 6) sagittal vertical axis (SVA), defined as the distance from C7 plumb line to superior corner of the sacral endplate (Figure 2).[17,18]
1.3Quality of Life Assessment
Quality of life assessment was performed based on the statistics and analysis of VAS and ODI scale. Patients were required to fill in the questionnaires at the time of consultation. Another spine surgeon was select to conduct the evaluation.
1.4 Statistical analysis
We used Statistical Packages of Social Sciences (SPSS) software (version 22.0) to analyze the data recorded, while the spondylolisthetic and spino-pelvic parameters were measured through Picture Archiving and Communication System (PACS). The inter-observer agreement of these parameters was expressed by interclass correlation coefficient (ICC).[19] ICC ranged from 0 to 1, and higher values suggested better agreement. Levels of agreement for ICC were divided into 3 grades, with ICC values 0.00 to 0.40 considered poor agreement, 0.40 to 0.74 fair to good agreement, and 0.75 to 1.00 excellent agreement.[20,21]
After the normality test, the data that obeys or approximately obeys the normal distribution is represented by mean ± standard deviation. The differences in imaging parameters and quality of life assessment between the two groups were compared by independent-sample t-test. Meanwhile, p values of < 0.05 were considered statistically significant for all the above.