Introduction: Sagittal imbalance is recognized as a significant variable that contributes to spinal deformity. Clinical outcomes after spine surgery are known to correlate with sagittal balance, which is traditionally measured by the C7-S1 plumb line as demonstrated on a 36-inch long-cassette film. Abnormal positive alignment induces compensatory changes within the cervical spine, including increased cervical lordosis and T1 slope. Patients presenting clinically with cervical pathology are not routinely assessed with long-cassette films. A validated tool that could determine the likelihood of overall spine malalignment using cervical radiographs alone would be of significant clinical value.
Methods: A retrospective review of 930 patients that were part of a prospectively collected, multicenter adult spinal deformity database was performed. The score was developed by a multivariable logistic regression model to predict a C7 plumb line greater than +50 mm. Variables including demographics, cervical lordosis, and T1 slope were analyzed. Patients were randomized in a 2:1 fashion into either a derivation or a validation cohort.
Results: Of the 930 patients, 384 (41.3%) had a positive sagittal balance. The final score for predicting SB greater than +50mm included: BMI >25 (1 point), age >55 years (2 points), and T1 slope >27o (2 points). A score = 4 had a specificity of 81.8% (CI95% 77.7 - 85.5%) and a sensitivity of 61.0% (CI 95% 54.6 - 67.0%). The ROC area under the curve was 0.82 (CI95% 0.78-0.85) and 0.81 (CI95% 0.76-0.86) in the derivation and validation cohorts, respectively.
Conclusions: This large multicenter study internally validated a score to assess sagittal balance based upon cervical radiographs, BMI, and age. The preoperative awareness of abnormal sagittal balance in patients with cervical pathology might change surgical treatment and clinical outcomes. Patients with high scores would benefit from long-cassette film evaluation.
Patient Care: The score described in this paper can be used to select patients with cervical disease that are at risk of having a pathological positive malalignment. Ordering a 36-inch long-cassette film in those patients can aid in surgical planning, defining risks and predict outcomes after surgery.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the importance of sagittal balance and its relation to clinical outcomes after surgery
2) Discuss, in small groups, how cervical parameters correlate with the C7-S1 plumb line
3) Discuss the clinical value of a score that can predict sagittal imbalance from a cervical radiograph and it clinical use
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