The influence of the magnitude of sagittal correction and local junctional factors on proximal junctional kyphosis and failure following correction of adult spinal deformity: an inverse probability weighted analysis

Abstract

Objective: Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) remain difficult problems following correction of adult spinal deformity (ASD). The goal of this study was to perform a comprehensive evaluation of risk factors associated with PJK and PJF using advanced statistical methods through inverse probability weighting (IPW).

Methods: Patients who presented to the authors' institution with symptomatic ASD from 2013 to 2021 and who underwent thoracolumbar fusion ending in the pelvis were included in the study. The primary outcomes were development of PJK and PJF following ASD correction. PJK was classified using Glattes' criteria. PJF was defined as a proximal junctional angle > 20° from preoperative measures or complications at the upper instrumented vertebra (UIV) including vertebral body fracture, instability, and/or hardware failure. Patient charts and images (radiography, CT, and MRI) were used to extract demographics, measures of sagittal and coronal balance on pre- and postoperative radiography, operative techniques, and bone health metrics. Propensity score generation with IPW was used to control for confounding variables.

Results: In total, 187 patients were included in the study with a median follow-up of 24.6 months. Sixty-nine patients (36.9%) developed PJK, while 26 (13.9%) developed PJF. Kaplan-Meier analysis showed that both PJK and PJF largely occurred within the 1st year of index ASD correction. IPW showed that patients who developed PJK had a larger correction in the sagittal plane including global lumbar lordosis (p < 0.001) and sagittal vertical axis (p = 0.020). PJF development was associated with factors at the UIV including low Hounsfield units (p = 0.026) and cranially directed screws at the UIV (p = 0.040).

Conclusions: PJK and PJF remain challenging postoperative complications following correction of ASD. In this large retrospective study that utilized IPW analysis, the authors found factors unique to each outcome. These results suggest that increased correction in the sagittal plane is more commonly associated with PJK, while junctional factors including bone quality and cranially directed screws at the UIV are associated with PJF. These findings can inform pre- and intraoperative medical and surgical strategies to reduce the incidence of PJK and PJF following ASD correction.

Keywords: adult spinal deformity; inverse probability analysis; proximal junctional failure; proximal junctional kyphosis; spinal fusion.