Unveiling the Impact of Reciprocal Changes in Thoracic Kyphosis After Staged Corrective Surgery in Adult Deformity.

Study DesignRetrospective cohort study.ObjectiveReciprocal changes (RCs) in unfused spinal segments can significantly affect the global alignment after corrective surgery. Identifying radiographic thresholds for guiding surgical strategies is critical for optimizing the outcomes.Materials and MethodsNinety-eight ASD patients who underwent staged surgeries, including lateral lumbar interbody fusion (LLIF) and posterior spinal fusion (PSF), were analyzed. According to the final follow-up image, the patients were classified into balanced (BG) and imbalanced (IG) groups, with IG further stratified into proximal junctional kyphosis/failure (IG-PJK/PJF) and non-PJK/PJF (IG-NPJK/PJF). Radiographic and clinical data were collected preoperatively, postoperatively, and at 2-year follow-up.ResultsThe IG exhibited greater RCs in thoracic kyphosis (TK) and PI-LL mismatch from postoperative to follow-up than the BG ( = .030, = .008). Significant predictors included Age >65.5 y/o (AUC: .672) and Post-PT >17.5° (AUC: .852) for imbalance and Post-TK >34.5° (AUC: .755) for IG-PJK/PJF. IG-PJK/PJF showed poorer ODI scores than BG and IG-NPJK/PJF ( = .021 and = .022, respectively). IG-PJK/PJF showed poorer total SRS-22 scores than IG-NPJK/PJF ( = .021).ConclusionIncreased RCs in TK was associated with adverse outcomes. Extending the upper instrumented vertebra (UIV) to the upper thoracic spine and addressing excessive TK (>34.5°) may improve alignment and reduce complications. Radiographic thresholds can provide actionable guidance in surgical planning.