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

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).

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.

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.

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.

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.