Influence of decompression surgery on sagittal balance parameters in patients with lumbar spinal stenosis

In this study we investigated the effect that lumbar decompression for lumbar spinal stenosis (LSS) has on sagittal balance and its clinical significance. This was an observational cohort study for LSS cases treated with decompression surgery. Core Outcome Measures Index (COMI), EuroQoL (EQ-5D) and Oswestry Disability Index (ODI) were used preoperatively and at 1 year follow-up. Pelvic incidence (PI), pelvic tilt (PT), sagittal vertical axis (SVA) and lumbar lordosis (LL) were measured before and 1 year after surgery. Hierarchical clustering (HC) was performed to identify subgroups with distinct patterns of variation. Ninety-five patients were included, mean age of 63 years, with good/excellent outcome in 71.6%. The median difference between postoperative and preoperative LL was - 1.3^o. Increased lumbar lordosis was correlated to ODI improvement (Pearson, r=-0.33). Three clusters were identified after HC. Patients in cluster 2 (31.6% ) had decrease in LL after surgery (mean values for cluster 1, 2, 3: 3.3^o, -5.6^o, 0.8^o), increase in SVA (-5 mm, + 25 mm, -19 mm) and no improvement in ODI (-23.1, 3.77, -17.1). Lumbar decompression has little effect in lumbar lordosis and sagittal balance. Cluster analysis yielded a subgroup of patients with worse outcomes, associated to decrease of LL and increase of SVA after surgery.