Abstract
Introduction
Predicting post-operative changes in thoracic kyphosis (TK) remains challenging in adult spinal deformity (ASD) surgery. This study aimed to quantify both iatrogenic and reciprocal changes in TK following lumbar correction and assess their maintenance at 2-year follow-up.Methods
A retrospective analysis was performed on 356 ASD patients treated with posterior instrumentation from T9-11 to the pelvis, with a minimum 2-year follow-up. TK values were compared with normative data. Multivariate analysis identified thoracolumbar parameters associated with reciprocal thoracic changes and proximal failure.Results
Pre-op TK (median 34°) was normal for 59.8% and hypokyphotic for 39.0% of patients. At 6 weeks, 79.1% of initially hypokyphotic patients normalized, while 11.3% of normokyphotic patients deteriorated. Postoperative TK increase correlated with lumbar lordosis gain (p2=0.40). Between 6 weeks and 2 years, 9.3% experienced TK decompensation >15°, and 9.6% required proximal extension for junctional issues-defined collectively as "thoracic failures" (17.4%). Independent predictors of failure included advanced age (OR 3.6), more proximal lumbar correction (OR 1.9), and pronounced early mid-thoracic kyphosis (OR 2.3).Conclusion
In ASD surgery with Upper Instrumented Vertebra (UIV) between T9 and T11, changes in TK were largely proportional to lumbar correction, leading to normalization in most cases. However, age, the location of lumbar correction, and early post-operative thoracic shape independently predicted thoracic failure, highlighting the need for tailored alignment strategies.