Proximal Junctional Kyphosis in Neuromuscular Scoliosis—a Risk Factor Analysis

Background/Objectives: Proximal junctional kyphosis (PJK) is one of the most frequently dis-cussed complications following corrective surgery in patients with neuromuscular scoliosis (NMS). Despite its clinical relevance, the etiology of PJK remains incompletely understood and appears to be multifactorial. Biomechanical and limited clinical studies have suggested that pre-operative hyperkyphosis, resection of the spinous processes with consequent disruption of poste-rior ligamentous structures, and rod contouring parameters may contribute as risk factors. Meth-ods: To validate these findings, we retrospectively analyzed 99 NMS patients who underwent posterior spinal fusion using a standardized screw-rod system between 2009 and 2017. Radio-graphic parameters were assessed preoperatively (preOP), postoperatively (postOP), and at an average follow-up (FU) of 29 months. Clinical data included age, weight, height, gender, and Risser sign. Radiological measurements comprised Cobb angles, thoracic kyphosis (TK), lumbar lordosis, levels of the upper (UIV) and lower (LIV) instrumented vertebrae, the number of fused levels, sagittal alignment parameters, the rod contour angle (RCA), and the mismatch between RCA and the proximal junctional angle (PJA). Patients were stratified into a PJK group and a non-PJK group. Results: The overall incidence of PJK was 23.2%. In line with previous biome-chanical findings, spinous process resection was significantly associated with PJK development. Furthermore, the PJK group demonstrated significantly higher preoperative TK (59.3° ± 29.04° vs. 34.5° ± 26.76°, p < 0.001), greater RCA (10.2° ± 4.01° vs. 7.7° ± 4.34°, p = 0.021), and a larger postop-erative mismatch between PJA and RCA (PJA−RCA: 3.8° ± 6.76° vs. −1.8° ± 6.55°, p < 0.001) com-pared to the non-PJK group. Conclusions: Spinous process resection, a pronounced mismatch between postoperative PJA and RCA (odds ratio [OR] = 1.19, p = 0.002), excessive rod bending (i.e., high RCA), and severe preoperative thoracic hyperkyphosis are significant risk factors for PJK. These variables should be carefully considered during the surgical planning and execution of de-formity correction in NMS patients.