Changes in spinal alignment after implant removal in adolescent idiopathic scoliosis.

PURPOSE: To evaluate the longitudinal evolution of coronal and sagittal spinal parameters following implant removal in patients previously treated with posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS). METHODS: Between January 2009 and December 2020, 1,650 patients underwent PSF for AIS: 25 required implant removal. Radiographic parameters assessed included proximal, main, and distal Cobb angles, thoracic kyphosis (TK), lumbar lordosis (LL), and pelvic parameters. Measurements were obtained pre- and post-PSF, pre- and post-implant removal, and at final follow-up. Longitudinal analyses used Friedman test and RM-ANOVA with adjustment for multiple comparisons and Pearson test was used for correlations. RESULTS: 25 patients (21 females; mean age 15.4 ± 1.9 years) were included, with a mean follow-up of 8.6 ± 3.9 years. The mean interval between PSF and implant removal was 5.8 ± 2.7 years. Immediately after removal, proximal, main, and distal Cobb angles increased significantly (+ 3.6°, p = 0.002; +7.3°, p < 0.001; +3°, p = 0.044). No significant further progression was observed at final follow-up. Median TK increased by 10° immediately after implant removal and by 14° at final follow-up compared with the pre-removal assessment (p = 0.019). LL and pelvic parameters remained stable. Exploratory ROC analysis suggested a potential association between implant removal before 74 months and greater TK progression (+ 9.4°, p = 0.043). Progression of the main thoracic Cobb angle correlated negatively with age at implant removal (r=-0.436; p = 0.029). CONCLUSION: Following implant removal after AIS fusion, moderate coronal deterioration and progressive thoracic kyphosis were observed, whereas lumbar and pelvic parameters remained stable. Early implant removal may increase the risk of postoperative kyphotic progression. LEVEL OF EVIDENCE: IV - Retrospective study.