Comparative Study of Treatment of High Grade Spondylolisthesis—Reduction Vs In-situ Fusion: Do we Need to Rethink Assessment of Pelvic Parameters?

Abstract

Introduction Reduction of high grade spondylolistheisis is considered to be the ideal treatment surgical treatment strategy on the premise that it restores spine biomechanics and altered sagittal balance. However it has been noted that in-situ fusion strategy also provide satisfactory result for high grade spondylolisthesis. In view of this observation we propose a hypothesis that following fusion L5 stands to be a part of the pelvis and pelvic parameter assessment should be considered with S1 pre-operatively and L5 post-operatively as the base of the pelvis. We assessd the pelvic parameters in this manner to guage the improvement in the pelvic parameters in both surgical groups (In –situ fusion Vs Reduction and fusion). Methodology: A retrospective review was conducted on 26 cases of high grade spondylolisthesis (defined as slippage > 50%) undergoing surgical treatment. Patients were divided into two groups; group one had undergone in-situ fusion and group two had undergone reduction with fusion. Spinopelvic parameters assessed for each group included; pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), lumbo-sacral kyphosis angle (LSK) and sacral femoral distance (SFD). Pre-operative spinopelvic parameters calculated with S1 were compared post-operatively with L5 as base of pelvis. Post-operative clinical outcomes were evaluated with Oswestry disability index (ODI score), Short form 12(SF 12) and visual analogue score (VAS score) for both groups. Results Mean age was 34.1 years and mean follow-up was 24.5 months. Following surgery, VAS and ODI improved from 7.7 to 1.8 and from 62.6 to 14.7% respectively with no difference between two groups. One patient had transient L5 deficit in the reduction groupne procedure over the other. The mean pelvic parameters preoperatively were PI - 68.5°, PT - 26.7°, SS - 41.7°, LL - 51.4°, SFD - 63.0 mm, shift of L1 plumb line - 63.9 mm and LSK - 67°. With L5 as the new sacrum, in reduction group, significant changes were noted in PT (60.4%), SFD (45.25%) and LSK (46.6%) (p < 0.05 for all). Similar significant changes were noted in insitu fusion also in PT (58.6%), SFD (41.2%) and LSK (68.6%) (p < 0.05 for all). In both groups, the changes in PI, SS and lumbar lordosis were not significantly changed. The above results show that insitu fusion achieves the same changes in sagittal parameters when L5 is considered as part of the new sacrum. Conclusions The spinopelvic parameters for in-situ fusion and reduction with fusion groups, when utilizing the superior endplate of L5 did not show significant change in PI, SS and LL for both groups. Three parameters changed significantly post-operatively in both procedures and showed comparable changes – PT, SFD and LSK. This may suggest that the improved clinical outcomes for both treatment strategy may co-relate to changes in PT, SFD and LSK. The findings call for reevaluating the need for risky reduction procedures to establish normal pelvic parameters.