Effect of Sacral Slanting on Coronal Balance and Residual Curve After Lumbar Curve Correction in Adolescent Idiopathic Scoliosis: A 5-Year Follow-up Study.

Abstract

Study DesignRetrospective cohort study.ObjectivesSacral slanting is defined as the angle between the horizontal line and the upper endplate of the sacrum in the coronal plane. This study evaluated changes in disc wedge angle (DWA) below the lowest instrumented vertebra (LIV) and coronal balance over a 5-year follow-up in patients with adolescent idiopathic scoliosis (AIS) with structural lumbar curve exhibiting sacral slanting.MethodsThe study included 118 patients with AIS and structural lumbar curves who underwent posterior fusion to L3 or L4, with a minimum 5-year follow-up. Radiological parameters were evaluated preoperatively and at 5 years and compared between LIV-L3 and LIV-L4 groups, with subgroup analyses for high (≥5°) vs low (<5°) sacral slanting within each group.ResultsPreoperative radiographs showed no significant differences between groups, except for the Cobb angle. In the LIV-L3 group, patients with sacral slanting ≥5° presented greater DWA at 5 years, whereas those with slanting <5° demonstrated a gradual decrease in DWA. In the LIV-L4 group, patients with sacral slanting ≥5° showed a progressive increase in C7-cervical sagittal vertical line, which was significantly greater at 5 years. Scoliosis Research Society-22 scores were similar between high and low slanting groups at the 5-year follow-up.ConclusionsIn patients with AIS and structural lumbar curve, increased preoperative sacral slanting was associated with an increased DWA below LIV when selecting LIV-L3. However, this increase does not progress over time. Conversely, selecting LIV at L4 in patients with high sacral slanting was associated with progressive coronal decompensation.