Evaluation of coronal alignment from the skull using the novel orbital–coronal vertical axis line

OBJECTIVE When treating patients with adult spinal deformity (ASD), radiographic measurements evaluating coronal alignment above C7 are lacking. The current objectives were to: 1) describe the new orbital–coronal vertical axis (ORB-CVA) line that evaluates coronal alignment from cranium to sacrum, 2) assess correlation with other radiographic variables, 3) evaluate correlations with patient-reported outcomes (PROs), and 4) compare the ORB-CVA with the standard C7-CVA. METHODS A retrospective cohort study of patients with ASD from a single institution was undertaken. Traditional C7-CVA measurements were obtained. The ORB-CVA was defined as the distance between the central sacral vertical line and the vertical line from the midpoint between the medial orbital walls. The ORB-CVA was correlated using traditional coronal measurements, including C7-CVA, maximum coronal Cobb angle, pelvic obliquity, leg length discrepancy (LLD), and coronal malalignment (CM), defined as a C7-CVA > 3 cm. Clinical improvement was analyzed as: 1) group means, 2) minimal clinically important difference (MCID), and 3) minimal symptom scale (MSS) (Oswestry Disability Index < 20 or Scoliosis Research Society–22r Instrument [SRS-22r] pain + function domains > 8). RESULTS A total of 243 patients underwent ASD surgery, and 175 had a 2-year follow-up. Of the 243 patients, 90 (37%) had preoperative CM. The mean (range) ORB-CVA at each time point was as follows: preoperatively, 2.9 ± 3.1 cm (−14.2 to 25.6 cm); 1 year postoperatively, 2.0 ± 1.6 cm (−12.4 to 6.7 cm); and 2 years postoperatively, 1.8 ± 1.7 cm (−6.0 to 11.1 cm) (p < 0.001 from preoperatively to 1 and 2 years). Preoperative ORB-CVA correlated best with C7-CVA (r = 0.842, p < 0.001), maximum coronal Cobb angle (r = 0.166, p = 0.010), pelvic obliquity (r = 0.293, p < 0.001), and LLD (r = 0.158, p = 0.006). Postoperatively, the ORB-CVA correlated only with C7-CVA (r = 0.629, p < 0.001) and LLD (r = 0.153, p = 0.017). Overall, 155 patients (63.8%) had an ORB-CVA that was ≥ 5 mm different from C7-CVA. The ORB-CVA correlated as well and sometimes better than C7-CVA with SRS-22r subdomains. After multivariate logistic regression, a greater ORB-CVA was associated with increased odds of complication, whereas C7-CVA was not associated with any of the three clinical outcomes (complication, readmission, reoperation). A larger difference between the ORB-CVA and C7-CVA was significantly associated with readmission and reoperation after univariate and multivariate logistic regression analyses. A threshold of ≥ 1.5-cm difference between the preoperative ORB-CVA and C7-CVA was found to be predictive of poorer outcomes. CONCLUSIONS The ORB-CVA correlated well with known coronal measurements and PROs. ORB-CVA was independently associated with increased odds of complication, whereas C7-CVA was not associated with any outcomes. A ≥ 1.5-cm difference between the preoperative ORB-CVA and C7-CVA was found to be predictive of poorer outcomes.