Effect of Sparing S1 Motion Segment on Spinopelvic-Sagittal Balance Relationship and its Impact on Pain and Functional Outcome: A Retrospective Cohort Study of Single Center Experience

Background: The relationship of the spine to the pelvis is the key determinant of the sagittal spinal alignment and is analyzed by the following parameters: The pelvic tilt (PT), the pelvic incidence (PI), the sacral slope (SS), lumbar lordosis (LL) and sagittal vertical axis (SVA). S1 instrumented fusion in cases of advanced degenerative spondylolisthesis affect different spinopelvic parameters thus requiring pre-operative comprehensive measurement of different parameters so as not to disrupt it postoperatively rendering it sagittally imbalanced thus more muscle strain to achieve balance is advocated result-ing in back pain. Aim of Study: To assess the effect of S1 motion segment sparing in the setting of degenerative spondylosis and its ef-fect on spinopelvic-sagittal balance parameters and long-term pain and disability using VAS (visual analogue scale) and ODI (modified Oswestry disability index-Arabic version). Material and Methods: 89 patients with multilevel lumbar canal stenosis underwent fusion surgery with or without S1 fix-ation were enrolled in the study. The patients were subsequently divided into 2 groups: S1 included (37 patients) and S1 sparing (52 patients); their clinical charts, radiological studies, and fol-low-up charts were retrieved and analyzed with special consid-eration on pre- and postsurgical parameters was done. Results: The mean Post-operative (LL) in S1 sparing group (37.57±7.89) while in S1 included group (12.2±2.69). The mean Post-operative (SS, PT) in S1 sparing group (26.95±10.8, 19.5±6.37) while in S1 included group (21.2±5.24, 28.3±6.97). The mean immediate Post-operative (VAS) in S1 sparing group Dropped from (7.56±0.87) to (4.12±0.97) while in S1 includ-ed group (7.59±0.96), while 6-12 Months follow-up VAS was (4.12±0.97, 4.95±1.31) in S1 sparing, S1 included respectively. Conclusions: S1 motion segment sparing in the setting of decompression and fusion of lower lumber spine seems to pos-itively impact the post-operative lumber lordosis, pelvic tilt and sacral slope with respect to sagittal balance parameters, hence muscle strain and energy expenditure of the adjacent level de-creased leading to better immediate as well as long term fol-low-up VAS, ODI scores compared to S1 inclusion.