Definitive Posterior Spinal Fusion After Magnetically Controlled Growing Rod Treatment in Early-Onset Scoliosis: A Single-Centre Longitudinal Analysis

Background. Early-onset scoliosis (EOS) is a complex condition requiring growth-preserving surgical strategies to allow continued spinal and thoracic development. Magnetically controlled growing rods (MCGRs) have become widely adopted for this purpose, as they enable non-invasive lengthening and reduce the number of surgical procedures during growth. While the outcomes of MCGR treatment during the lengthening phase have been extensively investigated, less attention has been devoted to the final stage of treatment, namely definitive posterior spinal fusion. In particular, limited evidence is available regarding radiographic outcomes and surgical strategies adopted at the time of final fusion, including implant density selection. Methods. This retrospective, single-centre study included ambulatory patients with idiopathic, neuromuscular, or syndromic EOS who completed a full course of MCGR treatment and subsequently underwent definitive posterior spinal fusion. Clinical and radiographic data were collected at predefined time points covering the entire treatment pathway, from pre-MCGR implantation to the last available follow-up after final fusion. Radiographic outcomes in the coronal and sagittal planes, perioperative variables, and postoperative complications were analysed. To evaluate the influence of implant density at final fusion, patients were stratified into low-density and high-density groups based on a cohort-derived threshold. Non-parametric statistical methods were used. Results. Definitive posterior spinal fusion provided additional correction of spinal deformity in both the coronal and sagittal planes, with maintenance of alignment at mid-term follow-up. Postoperative morbidity following final fusion was acceptable, despite the relatively high complication rate observed during the MCGR lengthening phase. Comparative analysis between low-density and high-density constructs did not demonstrate a significant advantage of higher implant density in terms of long-term radiographic outcomes. Lower-density constructs achieved comparable deformity correction without an increase in postoperative complications. Conclusions. Definitive posterior spinal fusion represents a safe and effective final step in the treatment of early-onset scoliosis following MCGR therapy. The findings of this study suggest that in this cohort, lower implant density at final fusion was not associated with inferior mid-term radiographic outcomes. However, given the exploratory nature of the analysis and limited statistical power, these findings should be interpreted with caution and require confirmation in larger prospective studies. These results support a tailored, biomechanically informed approach to implant density selection and provide a basis for future prospective studies in this field.