Progression of Thoracic Kyphosis After Lower Thoracic Fusion in Lumbar Flatback Deformity: Analysis of Risk Factors and Clinical Consequences

Study DesignRetrospective cohort study.ObjectivesTo investigate the risk factors and clinical impact of progression of thoracic kyphosis (PTK) in who underwent lower thoracic fusion for lumbar flatback deformity (LFBD).MethodsThe study included 170 patients (mean age 70.2 years; 90.6% female) who underwent fusion from the lower thoracic spine (T9 or T10) for LFBD with a minimum follow-up of 2 years. PTK was defined as a final thoracic kyphosis (TK) ≥ 40° and ΔTK ≥10°. Multivariate logistic regression was performed to identify independent risk factors for PTK. Receiver operating characteristic (ROC) curve analysis was used to determine predictive cutoff values.ResultsPTK developed in 55 patients (32.4%) during a mean follow-up of 35.8 months. Patients with PTK exhibited significantly higher final TK (48.2° vs 27.3°), worse sagittal alignment, and lower clinical outcome scores compared to those without PTK. Multivariate analysis identified preoperative TK (odds ratio [OR] = 1.120, <i>P</i> = 0.007) and age (OR = 1.094; <i>P</i> = 0.041) as independent risk factors for PTK. ROC analysis determined a preoperative TK cutoff value of 10.0° (area under the curve [AUC] = 0.834) and an age cutoff of 69.5 years (AUC = 0.661).ConclusionsIn this study, PTK developed in 32.4% of patients following fusion to the lower thoracic spine for LFBD. Advanced age (>70 years) and high baseline TK (>10°) were significant risk factors for PTK. Extending fusion to a more cephalad thoracic spine should be considered for patients at high risk of PTK development.