PurposeThere are still no data proving whether restoring the ideal sagittal profile (according to Roussouly classification) in adult scoliosis (AS) patients leads to any additional benefit, especially regarding mechanical complications. MethodsRetrospective analysis of operated AS patients recorded in a prospective multicenter database. Demographic and radiographic (preoperative and 6-week postoperative) data were analyzed. Patients with and without mechanical complications were compared looking especially at the surgical restoration of the ideal (based on Pelvic Incidence) sagittal profile. Univariate and multivariate analysis was performed to identify causes of mechanical complications at 2-year minimum follow-up. ResultsNinty-six AS patients were analyzed. Thirty-nine patients suffered a mechanical complication (18 PJK, 11 pseudoarthrosis, 10 screw pull-out), and 57 patients had no mechanical complications. Postoperatively, 72% of patients not matching the ideal Roussouly-type suffered mechanical complications compared to 15% of matched patients (P<0.001). Univariate analysis showed that older patients 64.913 versus 40.715.6 years (P<0.001), higher postoperative Global Tilt (27 degrees vs. 14.7 degrees) and Pelvic Tilt (25 degrees vs. 16 degrees) (P<0.001), upper instrumented vertebra at the thoracolumbar junction (62% vs. 21%) (P<0.001), fixation to the Iliac (76% vs. 6%) (P<0.001), and postoperative Roussouly-type mismatch (72% vs. 15%) (P<0.001) significantly increased the rate of mechanical complications. Multivariate logistic regression analysis selected: postoperative Roussouly-type mismatch (OR=41.9; 95%CI=5.5-315.7; P<0.001), iliac instrumentation (OR=19.4; 95%CI=2.6-142.5; P=0.004), and age (OR=1.1; 95%CI=1.02-1.16; P=0.004), as the most important variables.Conclusions Adult scoliosis surgery should restore the ideal Roussouly sagittal profile to decrease the rate of mechanical complications, especially in patients older than 65, instrumented to the pelvis.