INTRODUCTION: Adolescent Idiopathic Scoliosis (AIS) patients were previously demonstrated to walk with gait abnormalities preoperatively. Our objective was to compare preoperative to 2-year follow-up results using gait analysis in AIS patients undergoing posterior spinal fusion (PSF). MATERIAL AND METHODS: This is a retrospective single-center study. Patients with right thoracic curve, aged under 18 were included. They underwent low-dose biplanar radiographs preoperatively and at least 2 years after PSF. The day before surgery and at 2-year follow-up, quantitative gait analysis (QGA) was performed. Several gait parameters were recorded, such as sagittal and coronal thoracic and lumbar angles, dynamic CVA (dyn-CVA), dynamic SVA (dyn-SVA) and acromio-pelvis angle (APA). Motion of spine junctions were recorded (inflexion, flexion/extension and torsion). RESULTS: 49 patients were included (15.1 yo, 29.7 months FU). Main curve correction rate was 62.3 % ( ± 6.9). PSF led to a decrease in coronal thoracic and lumbar angles (13.2 vs -6° and -8.5 vs 0.9, p <
0.002, respectively). There was a significant decrease in Dyn-SVA (4.1 vs 3 cm, p <
0.002). Lumbo-sacral junction was significantly more in extension after spinal fusion (10.1 vs 14.4°, p <
0.002). APA changed from torsion toward the left to neutral position (-7.2 vs 0.0°, p <
0.002) with a significant decrease in range of motion (12.2 vs 9.6, p <
0.002). Increased lumbo-sacral extension was correlated to the number of levels fused (R=0.3740, p = 0.016). There was a positive correlation between LIV and the decrease of lumbo-sacral inflexion towards the right (R=-0.5036, p = 0.002). DISCUSSION: Our study reveals that PSF led to several changes in gait pattern of AIS patients, including complete correction of torsional abnormalities, mainly influenced by Cobb angle correction. We found that more distal LIV led to a decrease of lumbo-sacral inflexion motion, but the consequences of such changes in the long run remain unclear, especially on the onset of disc degeneration.