Preoperative Predictors of Postoperative C2 Tilt in Spinal Deformity Surgery: The Role of Pre-Op Alignment

Introduction: Achieving optimal sagittal alignment in spinal deformity surgery is critical for patient outcomes. In a prior analysis, we demonstrated that deviations from 0° in postoperative C2 Tilt (C2T) significantly increase the prediction error in the Δ Pelvic Tilt (PT) = ΔC2 Pelvic Angle (C2PA) - ΔC2T equation. However, identifying preoperative factors that predict postoperative C2T is equally important for improving surgical planning and predicting patient outcomes. This study aimed to identify the most significant preoperative predictors of postoperative C2T.

Methods: A retrospective analysis of spinal deformity patients (n = 104) was conducted. Postoperative C2T was analyzed using a multivariate linear regression model with potential predictors including BMI, Psoas Index, age at surgery, sex, ΔC2PA, Fusion Length, Hip Axis Alignment, and Pre-Op C2T. The aim was to determine which preoperative factors are associated with residual excess C2T postoperatively.

Results: The analysis confirmed that preoperative C2 Tilt was the strongest predictor of postoperative C2 Tilt (p < 0.001), with each degree of preoperative C2T leading to a 0.53° increase in postoperative C2T. Additionally, ΔC2PA was found to be a significant predictor (p < 0.001), with each unit that postoperative C2PA decreases there is a resulting in a 0.19° decrease in post-operative C2T. Age was also a significant predictor (p = 0.0117), where each additional year of age was associated with a 0.24° increase in postoperative C2T.

Conclusion : This study identified Pre-Op C2T, ΔC2PA, and age at surgery as significant predictors of postoperative C2T in spinal deformity patients. Intuitively, as global imbalance increases (i.e. greater pre-op C2T) there is associated potential for greater post-operative C2T despite meeting accepted alignment parameters such as the T4-L1 hip axis. Achieving a sufficient ΔC2PA is critical towards driving post-op C2T towards neutrality. Age seems to be an independent predictor of positive C2T – however it remains unclear if this is a senescent intrinsic drive for positive balance or if elderly patients were under corrected. Additional research is warranted to further study these relationships.