Efficacy of the spring distraction system for different etiologies of early onset scoliosis: evaluating an evolving treatment concept

PURPOSE: Early onset scoliosis (EOS) is a challenging condition that often requires "growth-friendly" implants to control the curve and accommodate spinal growth, especially in young patients with severe curves. The spring distraction system (SDS) was developed to support growth without the need for repeated lengthenings. This prospective cohort study aimed to compare the performance of the SDS between patients with different EOS etiologies. METHODS: We analyzed all SDS patients with a minimum of two-year follow-up. We measured curve correction, sagittal parameters, spinal growth, complications and unplanned return to the OR (UPROR) and compared these outcomes between different etiological groups. Differences between pre- and postoperative were compared with a mixed repeated-measures ANOVA. Differences between postoperative and later follow-up were compared using linear mixed models. Complications and UPROR rates were compared with a Kaplan-Meier survival analysis. RESULTS: Sixty-four patients were included (14 congenital, 41 neuromuscular, and 9 idiopathic). Mean age at surgery was 8.4 ± 1.7 years. Follow-up was 3.7 ± 1.4 years. Correction was maintained for congenital and neuromuscular patients. In idiopathic patients, Cobb angle increased during follow-up (3.6°/year). T1-S1 growth was 7.4 mm/year (idiopathic), 8.9 mm/year (congenital), and 9.8 mm/year (neuromuscular). Fifty-nine complications occurred (mostly implant-related), corresponding to a complication rate of 0.22/patient/year (congenital), 0.26/patient/year (neuromuscular) and 0.27/patient/year (idiopathic). Forty-two UPRORs were recorded, corresponding to an UPROR rate of 0.19/patient/year (congenital), 0.20/patient/year (neuromuscular) and 0.07/patient/year (idiopathic). CONCLUSION: The SDS performs well across EOS etiologies in terms of curve correction, spinal growth, and complication/UPROR rates. Idiopathic patients had less sustained correction. Complication rates were comparable, idiopathic patients had the lowest UPROR rate. TRIAL REGISTRATION: GRADS study (NL55705.041.16). BiPOWR study (NCT04021784).