Coronal imbalance after growing rod treatment in early-onset scoliosis: a minimum of 5 years’ follow-up

OBJECTIVE The objective of this study was to investigate the incidence and risk factors of coronal imbalance (CI) in patients with early-onset scoliosis (EOS) who underwent growing rod (GR) treatment. METHODS A consecutive series of 61 patients with EOS (25 boys and 36 girls, mean age 5.8 ± 1.7 years) who underwent GR treatment was retrospectively reviewed. Postoperative CI was defined as postoperative C7 translation on either side ≥ 20 mm. Patients were divided into an imbalanced and a balanced group. Coronal patterns were classified into three types: type A (C7 translation < 20 mm), type B (C7 translation ≥ 20 mm with C7 plumb line [C7PL] shifted to the concave side of the curve), and type C (C7 translation ≥ 20 mm and a C7PL shifted to the convex side of the curve). RESULTS Each patient had an average of 5.3 ± 1.0 lengthening procedures and was followed for an average of 6.2 ± 1.3 years. Eleven patients (18%) were diagnosed with CI at the latest distraction, 5 of whom graduated from GRs and underwent definitive fusion. However, these patients continued to present with CI at the last follow-up evaluation. The proportion of preoperative type C pattern (54.5% vs 16.0%, p = 0.018), immediate postoperative apical vertebral translation (30.4 ± 13.5 mm vs 21.2 ± 11.7 mm, p = 0.025), lowest instrumented vertebra tilt (11.4° ± 8.2° vs 7.3° ± 3.3°, p = 0.008), and spanned obliquity angle (SOA) (9.7° ± 10.5° vs 4.1° ± 4.5°, p = 0.006) values in the imbalanced group were significantly higher than in the balanced group. Multiple logistic regression demonstrated that a preoperative type C pattern and immediate postoperative SOA > 11° were independent risk factors for postoperative CI. CONCLUSIONS The incidence of CI in patients with EOS who underwent GR treatment was 18%. This complication could only be slightly improved after definitive spinal fusion because of the autofusion phenomenon. A preoperative type C pattern and immediate postoperative SOA > 11° were found to be the risk factors for CI occurrence at the latest follow-up.