The aim of this study was to investigate the impact of upper instrumented vertebra (UIV) screw angles on proximal junctional complications in patients with de novo degenerative lumbar scoliosis (DNDLS).

A total of 120 patients with DNDLS who underwent posterior long-segment instrumentation and fusion were included. Patients were divided into a proximal junctional kyphosis/failure (PJK/PJF) group and a non-PJK/PJF group. Radiographic parameters were measured, including UIV screw angle, UIV slope, UIV screw slope, fixed segmental angle (FSA), and spinopelvic parameters. Clinical and radiographic data were compared between the two groups. Multivariate logistic regression was used to analyze the independent risk factors of PJK/PJF. Receiver operating characteristic (ROC) curve analysis was used to determine the threshold value to predict PJK/PJF.

Thirty-six patients (30.0%) developed PJK or PJF during follow-up. Patients in the PJK/PJF group had a larger postoperative UIV screw angle, a larger postoperative UIV screw slope, and a larger postoperative PJA. A significant increase was observed in UIV screw angle from immediately postoperative assessment to the final follow-up in two groups (p < 0.001). Multivariate logistic analysis indicated that a larger positive postoperative UIV screw angle was an independent risk factor for PJK/PJF (OR 1.546, 95% CI 1.274–1.877). ROC curve analysis indicated that a UIV screw angle ≥ 1° is more likely to develop PJK/PJF. Compared with group A patients (UIV screw angle < 1°), group B patients (UIV screw angle ≥ 1°) had a higher incidence of PJK, PJF, UIV screw loosening, and worse functional scores at the final follow-up.

Avoiding insertion of cranially directed UIV pedicle screws may help prevent the development of PJK and PJF in patients with DNDLS.