Mismatch Between Proximal Rod Contour Angle and Proximal Junctional Angle: A Risk Factor Associated with Proximal Junctional Kyphosis After Growing Rods Treatment for Early-Onset Scoliosis

Study Design: A retrospective study Objectives: To investigate the impact of radiological and surgical factors as well as proximal rod contouring angle (PRCA) on the development of proximal junctional kyphosis (PJK) in early-onset scoliosis(EOS) patients after growing rod (GR) treatment. Methods: : We reviewed a consecutive series of EOS patients who had undergone growing rod (GR) treatment between 2009 and 2018 (minimum follow-up of 2 years) at a single institution. Patients were divided into PJK and non-PJK groups according to the occurrence of PJK or not during the follow-up periods. The demographic data, surgical strategies, and radiographic parameters were recorded and compared between the PJK and non-PJK groups. PJK was defined as a PJA＞10° at the last follow-up. PRCA was defined as the angle between the cephalad endplate of the UIV and the lower endplate of the second vertebra caudal to UIV and the PJA-PRCA was defined as the difference between the values of PJA and PRCA. Logistic regression was also performed to identify the risk factors for the occurrence of PJK. Results: : This study finally included 95 patients. The mean age at the index surgery was 6.5±2.2 years. Mean follow-up lasted 4.4±1.9 years. Lengthening procedures averaged 4.0 ± 1.8 times. There were 20 patients who were observed with PJK (the incidence, 21.1%). In comparison with the non-PJK group, the PJK group showed a larger preoperative coronal cobb angle (81.8±20.6° vs 70.4±12.4°, P=0.041) and global kyphosis (GK) (56.0±15.3° vs. 45.9±12.9°, P=0.044), as well as a larger GK correction (40.4%±10.0% vs. 30.0%±14.2%, P=0.035). In addition, the PJK group had significantly larger postoperative PJA (10.8±3.1 vs. 5.3±3.1, P＜0.001) and greater postoperative PJA-PRCA (5.3±3.0 vs. 3.66±2.9, P=0.031). The proportion of patients with a value of PJA-PRCA greater than 5° in PJK group was significantly higher than that in the non-PJK group. Multiple logistic regression showed that preoperative GK＞50°, postoperative PJA＞10 and postoperative PJA-PRCA＞5° were the risk factors in predicting PJK after GR treatment. Conclusions: : More than one-fifth EOS patients experienced PJK after GR treatment. Besides greater preoperative GK and larger postoperative PJA, PJA-PRCA mismatch may be an independent risk factor of PJK occurrence.