Does Preoperative Spinal Alignment Influence Surgical Outcomes When Postoperative Alignment and Fixation Strategies Are Matched in ASD Correction?

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STUDY DESIGN: Retrospective study. OBJECTIVE: To evaluate whether the extent of correction influences outcomes following adult spinal deformity (ASD) surgery using a matched-pair analysis. SUMMARY OF BACKGROUND DATA: Alignment targets are often based on achieving absolute values. However, the amount of correction may also influence outcomes. Existing studies are limited by methodological flaws, including multicollinearity and oversimplified modeling of correction. METHODS: We included ASD patients who underwent fusion (≥5 levels) with a UIV between T1 and L1 at a single center (2013-2023), with ≥1-year follow-up. Clinical, radiographic, and surgical outcome data were collected. Patients were 1:1 matched based on T4-L1PA mismatch and L1PA offset (±3°), UIV region (upper vs . lower thoracic), and pelvic fixation status (yes/no). Collected variables were then transformed into within-pair differences (Δ) (absolute value) (for continuous/ordinal variables) or classified as concordant/discordant (for binary variables). Outcomes were analyzed as within-pair Δ or concordance using linear or logistic regression, respectively, with within-pair Δpreoperative alignment as the main predictor and clinical covariates adjusted. RESULTS: A total of 114 patients were matched for similar postoperative sagittal alignment and fixation strategy, forming 57 pairs. Among matched pairs, the average within-pair Δpreoperative alignment (reflecting correction magnitude) was as follows: Δmax Cobb 24.2±18.2°, ΔSVA 76.6±53.2 mm, median ΔL1PA offset 5.0° (IQR 2.3-8.2°), and ΔT4-L1PA 6.9±4.7°. No significant associations were observed between within-pair Δpreoperative alignment and ΔODI, Δlength of stay, or Δoperative time. Similarly, within-pair Δpreoperative alignment did not influence binary outcomes including PJK, PJF, reoperation, complications, or discharge disposition. CONCLUSION: In patients who achieved similar postoperative alignment and fixation strategies, the baseline deformity (or the amount of correction) did not independently affect postoperative outcomes. Achieving target postoperative alignment rather than the extent of correction should remain the primary focus of surgical planning to optimize recovery and reduce complication risk. LEVEL OF EVIDENCE: Level III.

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