Proximal junctional kyphosis in distraction-based growth-friendly treatment: Definition, risk factors, and timeline.

PURPOSE: To identify risk factors and characterize the timing and nature of proximal junctional kyphosis (PJK) following dual-rod distraction-based growth-friendly treatment (DB-GFT) in early-onset scoliosis (EOS). METHODS: Ninety-five EOS patients (37 male, 58 female) treated with dual growing rod systems between 2004 and 2023, with ≥ 2 years of follow-up, were retrospectively reviewed at a single center. Radiographic parameters were assessed preoperatively, postoperatively, and at final follow-up. PJK was defined as a proximal junctional angle(PJA) ≥10° at final follow-up with an increase of ≥10° compared with preoperative measurement. Serial lateral radiographs were evaluated at 3 or 6 month intervals to determine occurrence and timing of PJK. Univariate and multivariate logistic regression analyses were performed to identify risk factors. RESULTS: The mean age at index surgery was 6.8 years, with a mean follow-up of 5.8 years. PJK developed in 17 patients (17.9%): 3 immediately postoperatively(mechanical) and 14 gradually (biological), of whom 12 were diagnosed after the first year. Univariate analysis identified UIV at T3 or below and T5-T12 kyphosis correction ≥ 30° as significant risk factors. Each 1° increase in preoperative T5-T12 kyphosis increased PJK risk by 3%. Multivariate analysis confirmed preoperative T2-T12 kyphosis ≥45° and UIV at T3 or below as independent risk factors. CONCLUSIONS: While extensive kyphosis correction was identified as a significant risk factor on univariate analysis, preoperative T2-T12 kyphosis ≥45° and UIV at T3 or below emerged as independent predictors, underscoring the importance of both preoperative sagittal alignment and UIV selection in surgical planning. Segment-adjusted PJA values may better identify clinically significant cases at risk of progression to proximal junctional failure. As most PJK develops after 1 year, long-term follow-up is essential. THE SIGNIFICANCE OF STUDY: Distal upper instrumented vertebra (T3 or below) and preoperative T2-12 thoracic kyphosis significantly increase the risk of proximal junctional kyphosis, which most commonly develops after the first postoperative year.