Junctional factors and magnitude of sagittal correction have differential effects on development of proximal junctional kyphosis and failure following correction of adult spinal deformity

Introduction: Proximal junctional kyphosis (PJK) and failure (PJF) remain unsolved complications following adult spinal deformity (ASD) correction. The goal of our study was to perform a comprehensive evaluation of risk factors for PJK/PJF using advanced statistical methods through inverse probability weighting (IPW), which helps control for confounding variables that limit retrospective studies.

Methods: Patients were retrospectively enrolled in our study who underwent thoracolumbar fusion with pelvic instrumentation for ASD from 2013-2021. The Glatte’s criteria was used to define PJK. PJF was defined as an increase in proximal junctional angle (PJA) >20 degrees, UIV fracture, hardware failure, or junctional instability. Several clinical, demographic, operative technique, and imaging (spinopelvic measurements and CT housnfield units) variables were extracted from the health record. Propensity scores were generated to control for age, gender, race, BMI, and ASA. For continuous outcomes, depending on the distribution, t-tests or generalized linear models were used to test for differences between groups. For categorical outcomes, differences between groups were tested with Fisher’s Exact Test.

Results: 187 patients were included (24.6 months median follow-up). PJK developed in 69 (69.9%) patients, while PJF occurred in 26 patients (13.9%). IPW analysis revealed that patients with PJK had a larger magnitude of sagittal correction by SVA (p = 0.020) and global lumbar lordosis (p < 0.001). Conversely, patients with PJF were more likely to have low Hounsfield units at the UIV (p = 0.003) and cranially directed screws (p = 0.004).

Conclusion : After balancing confounding variables, IPW analysis revealed that PJK and PJF have unique risk factors. Our data implies that larger sagittal plane corrections increase the risk of PJK, while local factors at the UIV including bone quality and screw direction influence PJF. These findings can be used in preoperative and intraoperative decision making to mitigate PJK/F development after deformity correction.