Effect of sparing S1 motion segment on spinopelvic-sagittal balance relationship and its impact on pain and functional outcome

Purpose: To assess the effect of S1 motion segment sparing in the setting of degenerative spondylosis and its effect on spinopelvic-sagittal balance parameters and long-term pain and disability using VAS (visual analogue scale) and ODI (modified Oswestry disability index-Arabic version). Methods: 89 patients with multilevel lumbar canal stenosis underwent fusion surgery with or without S1 fixation 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 follow-up charts were retrieved and analyzed with special consideration on pre- and post-surgical 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 included 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 positively 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 decreased leading to better immediate as well as long term follow up VAS, ODI scores compared to S1 inclusion.