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C2 Coronal Angle (C2C): A Novel Predictor of Outcomes Following Adult Thoracolumbar Spinal Deformity Surgery
Nikita Lakomkin1, Anthony L Mikula1, Robert K Eastlack2
1Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota.
Study Design:
Retrospective analysis of a multicenter series of deformity patients undergoing thoracolumbar instrumentation to the pelvis.
Objective:
Introduce the C2 coronal angle (C2C) as a novel metric, assess its association with quality-of-life and neck-specific outcomes, and compare the strength of this association with the traditional linear C7-CSVL offset.
Summary Of Background Data:
While assessment of the sagittal plane incorporates vertebropelvic angles for surgical planning, angular coronal measurements have not been evaluated as predictors of patient-reported outcomes following adult spinal deformity (ASD) surgery.
Methods:
Demographics, comorbidities, and radiographic parameters were collected preoperatively and at 2-year follow-up. Coronal angles were measured between CSVL and the center of the C2 body (C2C). Primary endpoints were patient‑reported outcomes at two years (SRS‑22, SF‑36, NDI) and whether patients achieved the minimal clinically important difference (MCID). Univariable and multivariable regression models examined the relationship between C2C and PROMs. An ROC analysis with Youden's Index identified optimal C2C thresholds for predicting NDI >20.
Results:
Among 328 patients (mean age 64.0 years, 12.6 levels fused), postoperative absolute C2C was independently associated with PROMs. Each 1° increase in C2C was associated with decreased 2-yr SRS-Total (P=0.014) and activity (P=0.024), pain (P=0.033), and mental health (P=0.029) subdomains. Each 1° increase reduced odds of achieving NDI MCID by 34% (OR=0.66, P=0.022). ROC identified an optimal C2C threshold of 3.5°. Patients exceeding this had nearly twice the odds of neck disability (OR=1.90, P=0.049) and significantly lower SF-36 Physical Component (P=0.004) and Physical Functioning (P=0.011) scores. C2C was more strongly associated with SRS-Total than C7-CSVL (AIC=657 vs. 660; adj. R²=0.058 vs.0.048).
Conclusions:
Achieving postoperative C2C ≤3.5° is independently associated with reduced neck disability and optimized quality of life after ASD surgery. C2C was more strongly associated with SRS-Total than C7-CSVL and could be considered as a complementary measure of coronal alignment.