Different Risk Factors of Proximal Junctional Kyphosis and Proximal Junctional Failure Following Long Instrumented Fusion to the Sacrum for Adult Spinal Deformity: Survivorship Analysis of 160 Patients

<jats:title>Abstract</jats:title> <jats:p> <jats:bold>BACKGROUND:</jats:bold> The failure modes, time to development, and clinical relevance are known to differ between proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). However, there are no reports that study the risk factors of PJK and PJF separately.</jats:p> <jats:p> <jats:bold>OBJECTIVE:</jats:bold> The aim of this study was to investigate the risk factors for PJK and PJF separately.</jats:p> <jats:p> <jats:bold>METHODS:</jats:bold> A retrospective study of 160 consecutive patients who underwent a long instrumented fusion to the sacrum for adult spinal deformity with a minimum follow-up of 2 years was conducted. A separate survivorship analysis of PJK and PJF was performed using the Cox proportional hazards model for the 3 categorical parameters of surgical, radiographic, and patient factors.</jats:p> <jats:p> <jats:bold>RESULTS:</jats:bold> PJK developed in 27 patients (16.9%) and PJF in 29 patients (18.1%). The median survival time was 17.0 months for PJK and 3.0 months for PJF. Multivariate analyses revealed that a high body mass index was an independent risk factor for PJK (hazard ratio [HR] = 1.179), whereas the significant risk factors for PJF were older age, the presence of osteoporosis, the uppermost instrumented vertebra level at T11-L1, and a greater preoperative sagittal vertical axis (HR = 1.082, 6.465, 5.236, and 1.017, respectively). A large correction of sagittal deformity was shown to be a risk factor for PJF on univariate analyses, but not on multivariate analyses.</jats:p> <jats:p> <jats:bold>CONCLUSION:</jats:bold> PJK developed at a median of 17 months and PJF at a median of 3 months. A high body mass index was an independent risk factor for PJK, whereas older age, osteoporosis, uppermost instrumented vertebra level at the thoracolumbar junction, and greater preoperative sagittal vertical axis were risk factors for PJF.</jats:p>